Io’s Pillan Patera eruption in 1997: the largest lava falls ever seen

Photo: Galileo Spacecraft, right showing the dark pyroclastic deposit produced by Pillan’s lava fountains and as well the dark lava flows themselves. Pillan patera is much larger than any individual lava flow eruption that has been observed recently on Earth. The large red ring is sulfur allotropes from Pelé’s lava lake to the left that has its own dark pyroclasts from lava fountains as well.


Photo Galileo Spacecraft, Pillan sleeps in 1996, Pillan Pateras caldera walls casting shadows. One year later it would be covered in fresh basalt flows. The bright stuff is probably sulfur gasses that froze. The whole area is covered by thick deposits of ”sulfur snow” from other volcanic vents.

Jupiter’s Moon Io is the most volcanic place in the solar system. The most powerful active volcanoes known to exist cannot be found here on Earth, but on Io, a small moon of Jupiter, and it is therefore an enormous fascination for me. Io is a volcanic powerhouse, so volcanic it is very much a real-world” Mustafar”. Io is so volcanic because of tidal forces from Jupiter and the rest of its moons so it is more like the planets were like in the Hadean era than any modern-day moon or planet. Io’s intense volcanism surprised everyone in 1979 during the Voyager era. It is the most volcanic place in the solar system and it is just a small moon, that was so unexpected, indeed a complete shock of what to expect from a moon in the outer solar system, where it is very cold and presumably very dead. Instead, they discovered a celestial object that is in many ways more interesting than the other planets themselves. This is my first article on a specific Ionian eruption, one of many in the last 20 years.

The Ionian eruption at Pillan Patera 1997 involved one of the most spectacular basaltic volcanic events ever seen by instruments, an event so spectacular it deserves its own article for Volcanocafe. The event involved the largest lava falls ever seen as an effect of filling a Patera ( Ionian caldera ) with lava from a fissure eruption. In this article, I will talk about this event that was the first time a major lava flow fissure eruption event was seen on another celestial body in some detail.

This eruption resulted in a dark, pyroclastic deposit more than 400 kilometres (250 miles) across, and a fresh dark lava flow emplaced with an area of 5000 square kilometres. There have been other more intense Ionian eruptions in thermal output since then, like 1990, 1991, 2000, 2010 and 2020 events that may have done ten’s of km3 in an hour, but in terms of scenery, Pillan Patera perhaps wins the contest. Still, the February 2001 Surt eruption produced 100 times more energy than Pillan Patera did in thermal emissions.

Io is truly an extraordinary moon, and the eruption at Pillan definitively proved that not only Earth has hot active silicate volcanoes in this solar system. Almost 30 years ago while the poor atmospheric probe was disappearing into the jovian abyss, the Galileo mothership itself put on the brakes and slipped into orbit around Jupiter. The staff at JPL knew when they entered orbit in 1995 that Io would be the most fun among the Jovian satellites, and what they discovered was extraordinary. Io bubbles with volcanoes, very large powerful volcanoes too and because of that I will write a separate article later about Ionian volcanism in general. Jupiter’s moon Io is so unique and strange compared to other moons in the solar system, that it almost borders on Sci-Fi.

The opening of the 1997 event far exceeded historical lava fissures in strength, One reason for this is that more magma was available, but it is also because magmatic gases expand more violently in a vacuum. So the lava fountains at Pillan and other fast ”outburst type” eruptions on Io are extraordinarily violent. The eruption continued for months at high intensity and was seen numerous times by the Galileo mothership from its many orbit flybys of Io. The intense thermal emission and creeping warm dark flows were a sure sign of a large-scale emplacement of fast lava flows. At peak output, the Pillan Patera eruption outshone all other Ionian volcanoes combined. Even before the Galileo mission violent lava fountains have been proposed to be the cause of such powerful thermal emissions. These outbursts on Io provided one of the best opportunities to measure the temperatures of Ionian lavas because of the sheer amount of hot materials exposed. Despite the sheer size of the event, it had many similarities to large-scale fissure eruptions that have been seen on Earth. Pillan’s eruption was the first high eruption rate Ionian eruption seen at close view, so fast high output Ionian fissure lava eruptions have been given the name ”Pillanian eruptions”. The event was a wake-up call of how volcanic Io is compared to Earth and a sure sign of high-temperature silicate volcanism on a body outside the Earth. It surprised the experts at JPL even if eruptions had been seen there in 1979. The eruption at Pillan formed the largest lava falls ever seen from remote instrument sensors and is the main reason I wanted to write this article about this Ionian eruption and the events that made it so spectacular. Despite the few photos and data taken from this alien eruption, a surprising amount was learnt from what was recorded by Galileo. While the lava falls are the main star of this extraterrestrial eruption I of course need to explain the eruption itself as well.

The name Pillan itself comes from Mapuche (Araucanian) peoples of Chile. Pillan is a god of thunder, volcanoes and fire and is said to reside in many Chilean volcanoes, like Villaricca (Ruka Pillañ or Quetrupillán as examples), but on Io, Pillan was given a far grander home for sure as Ionian volcanoes dwarf these. On Io, all volcanoes and volcanic features have to be named after gods, demons, mythological beings of fire, earthquakes or the sun. Below follows an explanation of the year 1997 Ionian eruption 25 years ago and its high points of fun and fascination.

The 1997 eruption site and lava flows

Photo Galileo Spacecraft: filling of the Pillan Patera was the largest lava falls ever seen so far as many 10s of km3 of lava cascaded into the caldera pit. The greenish-olive colour of the lava is from chemical reactions as sulfur snow and volcanic gases freeze and settle on hot fresh basalt. The dark flows in 1996 are clearly from an earlier smaller eruption.

During the Voyager era and the very first Galileo probe years, Pillan was a quiet region, a 70 km wide and 3 km deep ”caldera”, called a ”patera” in planetary geology. It was dusted with sulfur snow from the nearby volcano Pele. To the west of the caldera was a rifted mesa and the mountain ranges of Pillan Mons. Only a very small thermal hotspot and an older flow field in this area was suggesting any active silicate basaltic volcanism. Galileo’s probe arrived at Jupiter’s system on December 7 1995. That it arrived at all was a triumph of technology and solutions to stubborn problems. Still, the Galileo mothership was not without issues. The biggest plague was that the HGA antenna failed to open leaving the probe with reduced data capabilities with the Low Gain Antenna. But the probe was still very capable of photography and collecting sensor data.

Galileo returned to the inner Jupiter system orbits in late June 1997 during orbit C9, allowing an eruption to be seen in daylight and an eclipse on June 28, 1997. In the case of images returned back, a new plume fallout  ~110 kilometres tall was observed over Pillan on the limb of Io. Before that observation, no earlier volcanic plume had ever been observed at Pillan. On June 28 1997 (during orbit C9) a massive eruption just east of the mountain complex was in progress. The thermal emission was so intense that even at 1.4 million kilometres distance it overloaded Galileo’s SSI instrument. A 140 km high silicate tephra plume shot up from it as well with an intense thermal radiation emission at its base. What happened was a huge intrusion of gas-rich basaltic magma had reached the surface, resulting in a long line of violent lava fountains showering 1000s of square kilometres of the surface with molten lava, Galileo’s instruments also showed a creeping expanding dark area in visible light, but that also was very hot in the infrared and was large scale turbulent lava flows fed by the lava fountains from the fissures.

Large powerful eruptions like these at Pillan and other similar Ionian outbursts erupt from vast fissure systems, with fissures many 10’s of kilometres long. This is certain for Pillan’s eruption fissures, looking at the few photos that were taken: the fissure system appears to perhaps be 50 kilometres long, or because the lava flows emerged from a line, that may give the fissure system a length of 75 – 80 kilometres when compared to the 75 km wide Pillan “caldera”, that exceeds even large historical Icelandic rifting eruption fissures in length. But because spacecraft imagery resolution of the eruption site itself is low, we will never know for sure how long the eruption fissures were at Pillan, but many 10s of kilometres of lava fountain curtains are certain, like fiery walls going up into the void. From low orbit Pillan’s start would be a spectacular sight at the night terminator of Io, its gas plume would be seen as a faint blue dome as it scatters the sun’s light with an intensely glowing spot at its centre, which is the violent start of the eruption. On the ground, effects almost similar to a Plinian eruption on Earth probably happened with the massive lava fountains throwing out an ejecta plume with falling materials around them as seen with the dark pyroclastic sheet left by the eruption around the lava flows. The start-up of the 1997 eruption must have been a formidable sight with miles-long walls of calbuco-like glowing pyroclastic fountain columns when eruption rates were at their most intense. The violent opening of the eruption could have been many 100,000s of cubic meters a second, while the lava flows flowing out from the enraged moon was fed at 10,000s to 100,000s of cubic meters a second at the first phase of the eruption, declining to many 1000s of cubic meters a second as the eruption vented on for months. Despite the sheer violence of it, it all happened in the silent vacuum of airless Io, it was a geological rock concert without sound, spraying lava into the silent void. The long-term eruption rates for the Pillan eruption have been estimated at 6000 – 8000 cubic meters a second with a much faster start for quite a while. The Holuhraun eruption had around 250 to 300 cubic meters a second, to make a comparison to Ionian eruptions. Even at average lava flow output Pillan was somewhat or even much higher than Laki lava flow emplacement, with its start far exceeding terrestrial fissure examples. Estimating eruption rates from only a few handfuls of hot pixels and grainy closeups is a complicated mathematical process.

At these eruption fissures, massive lava fountains kept going for months or even years with decreasing intensity. Most of the lava volume emplaced by Pillan 1997 was likely emplaced during the first weeks. Io’s low gravity and lack of atmosphere means lava fountains are much larger than on Earth. The fountains would probably be many kilometres tall and throw out large amounts of lava as sulfur gas nucleation in the magma conduit is much more violent than on Earth in Io’s vacuum, spraying lava pyroclasts on ballistic trajectories in all directions. The inner part of these huge fountains are very thermally and optically dense, so the lava clasts heat each other by their own radiation and the lava doesn’t cool much as it was thrown everywhere feeding the clastogenic lava flows from the fissure system. These huge fountains can be thought of as liquid-gas geysers when a magmatic sulfur volatile violently decompresses driving the magma curtains miles into space. It probably goes up with the speed of a high-powered rifle, and during the long fall down the pyroclasts also hit the Ionian ground at high speed, leaving impact craters in earlier pyroclastic sheets. Because of the lava fountains spraying tephra everywhere, an imaginary visitor on the ground near Pillan may experience a constant stone rain of crumbly gassy mafic pyroclasts and visibility would likely be poor. The Galileo Spacecraft later pointed its instruments spectrometers at the eruption deposits and discovered Inosilicate minerals in the group of orthopyroxenes. The mineral enstatite was identified and it may suggest pure ultramafic lava was involved in the event rather than normal basaltic lava, or perhaps even a mafic silicate basalt composition unique to Io. The discovery of mafic minerals in this eruption confirmed the presence of high-temperature silicate magmas on Io. Lava fountains on airless Io should behave exactly the same as lava fountains would do on Earth’s airless moon and may result in similar volcanic deposits. Apollo 17 astronauts discovered deposits of small glass spheres near old fissures on the Moon that were the result of volatile rich lunar lava fountains, the same lava droplets surely was produced in the Pillan event and was deposited far and wide. The pillian eruptions dark pyroclastic deposits helped researchers to identify what all the other Ionian colors are from. Pale deposits are sulfur snow that froze out, while dark diffuse deposits are the tephra fallout from silicate lava fountains.

The eruption’s energy and superheated gases thrown out formed a vast plume of dark basaltic tephra and sulfur gas that fans out in a dome like plume shape and rains down over a 400 kilometers wide spot. Pillan’s lava fountains rained these dark silicate rich tephra over a vast region. The lighter sulfur gases plume rose to 140-km-high similar to the constant gas plume that exist over Pele’s Lava lake just to the west of Pillan, the sulfur gas ejected by this eruption spread out as a dome and would scatter blue light, so near the eruption site any space traveller walking the surface would perhaps see a dark blue sky and a fiery plume going up into it. It is a spectacular light show, any imaginary expedition team in metal clad suits, likely dazzled in awe as the area east of Pillan Mons becomes a huge wall of ”fire” as the gas rich dyke reached the surface sending countless lava pyroclasts that fills the skies like meteors. Lava fountains like fiery geyser pillars also erupt from Pillan Mons itself. This is a rifted mesa plateau and probably was used as an easier pathway for the ascending magma as many Ionian lava lakes and lava flows do emerge from leaky faults along crustal blocks. Similarly fault guided, caldera fault eruptions have also been seen at other violent outburst eruptions like the Tvasthar Catena eruptions that had some similar dynamics as the Pillan Patera eruption.

Photo by Galileo Spacecraft. The only ultra close-up photo that was taken of the lava flow’s surface that was emplaced at Pillan at Io. Notice the dark slabs as large pieces of crust were rafted with the raging lava flow. In later phases of the eruption there were lava channels clearly seen as well.

Violent Ionian eruptions can be thought of as ”sulfuroaticmagmatic” eruptions as the rising hot magma interacts violently with thick layers of sulfur ice in the low density volatile Ionian crust. Such interactions may cause even more volatile release in the already decompressing volatiles. Here on Earth same phenomena happens when magma erupts in a glacier or in waterlogged ground. On Io it happens when magma gets crammed in together with sulfur ”ice”. But most of the eruption pressure at Pillan came from decompressing pre-existing magmatic sulfur volatiles.

On October 11, 1999, Galileo performed its first close Io passover since the spacecraft entered orbit around Jupiter in December 1995 just after I was born. The close range of the encounter over Io’s trailing hemisphere provided a chance for Galileo’s cameras to observe the new still warm Pillan lava flows that had flowed out in the years before. They were photographed at high resolution (9-18 meters or 30-60 feet per pixel). Unfortunately most of the images were mostly scrambled, requiring extensive processing to bring out useful information. Despite the attempts of processing these closeup photos, most of the images were heavily degraded by radiation, and included a dark stripe down the center of each frame. The cropped full-frame mode image, shown at the lower left of the above mosaic, did not suffer from this anomaly. A rough lava flow emplaced a broad sheet (rather than a channelized flow) was revealed in the close-up photo of the lava flows, with pits and lava channels across parts of the flow. By looking at length of the shadow along the edges of the new lava flows on the left and right sides of the mosaic, the Pillan lava flow had an average thickness height of 8-11 meters and had a slabby Aa structure at the front and sheet pahoehoe at the middle, In fact most Pillan flows had a ”flood pahoehoe” appearance. The features that were seen in Pillan’s flows are quite similar to the flood lavas on Mars that been seen in the Athabasca Valles region that consist of thin lava flows with large chunks of rafted crust. This is a sure sign they too was formed from lava flows rather than water or mud. These lava flow surfaces are quite rare on Earth and only some really fast historical fissure eruptions in Iceland, Hawaii and Africa have produced similar surfaces. The raging lava flows that engulfed ionian ground at Pillan was probably partly turbulent at least near the fissures, could also explain the chaotic mix of slabby and sheeted pahoehoe that was seen the close-ups from the Galileo Spacecraft during its close pass in 1999 when most of the eruption had died down, most of the lava was quick laminar flows and formed a lava flow surface, that is neither Aa or pahoehoe but something that is reserved only for very fast eruptions.

Lava flows emplaced, fed at an estimated many 10s of thousands of cubic meters a second, flowed south towards the Pillan Patera. At these high eruption rates it would be a massive, fast moving sheet Aa or pahoehoe mix flows fed by fluid open channels. Near the vent fountains it would be flowing at car speeds over kilometers wide fronts, erupting cubic kilometers in just hours. Further away from the fissures the energy of the flow would be spread out and the moving lava front would flow slower. Still, many lava flow fronts each 30 km wide and 11 m high would be quite a sight indeed, moving at a few kilometers a day towards the caldera pit of Pillan Patera. The massive lava flows would engulf thick layers of sulfur snow quickly, and especially so during the first days and weeks of eruption when flows where fastest close to the vents. That would result in spectacular ”phreatomagmatic” explosions when hot lava engulfed these volatile frosts. On IO this is possible as well if such fast moving lava flows would flow over a ”sulfur glacier” or thick layers of sulfur snow/ frost.

Most of the flow emplacement style at Pillan was probably large single ”sheet type pahoehoes” not unlike those close to the vents of Mauna Loa lava flows but on a much larger scale, with a very violent opening, and miles long curtains of fire with vast sheets flowing out. Later the vent erodes the conduits forming more gentle activity, the later stages of the eruption likely had an impressive lava channel system when the eruption focused on a few locations rather than miles long fountain fissures. With such intense eruption rates all the lava simply flows away from the rift system without forming any spatter ramparts. Eruptions like these maybe analogous to ancient lunar mare eruptions with basalt flooding large areas, with Io’s Pillan eruption being a slightly smaller version of lunar ”mare eruptions”

Photo: Opening of Pillan Patera eruption would be an incredible sight as many 10s cubic kilometers of hot lava rapidly flood Io’s surface. The opening of the 2015 Wolf eruption provides a much smaller version of that. On Io the spectacular sight of an enraged moon’s lava fountains and a looming Jupiter in the background would make quite a sight.

Photo by Galileo Spacecraft showing Pillan Patera caldera as it got filled by dark fresh lava. The darkest spot is the lava flows, and the dark halo around it is the pyroclastic deposit formed by lava fountain fallout

The rough crumbly texture of the Pillan lava surfaces was likely the result from a number of factors, including the interaction between the hot lava and the cold, volatile-rich surface it flowed over, high eruption rates and low viscosity encouraging turbulence, and the disconnect between the high effusion rate (the volume of lava flow for each meter of the vent fissure) and the speed of the flow front. In the first case, gas created by the heating of sulfur dioxide when fast moving lava flows buries it would explode through the cooled crust of the lava flow. This action would rip up the cooled lava crust and likely formed ”phreatomagmatic” vents that provide even additional gas for the plume seen from Pillan in 1997. On Earth and Mars when large amounts of fast moving lava quickly engulf a wet or volatile ground that may also result in formation of pseudocones. Such interactions have been confirmed in martian pseudocones. One such channel can be seen in the left side of the mosaic. A very fast lava effusion flow within the lava flow ( many 10 000s of cubic meters a second) would cause the outer cooled crust to break up into blocks or rafts. These rafts flowing with in the lava river stream can also disturb the cooled crust as it is moved downstream by the still molten lava beneath. It would be a spectacular sight for sure, a little like an ice flood, with huge slabs and sheets of crust and large lava bergs moving in a fast moving lava stream, but being fiery hot instead of the cold colors of water. In terms of appearance the fast moving lava flows at Pillan or at least the flood sheet channels maybe very similar to the lava flows seen at Mustafar in Star Wars Ep 3 Revenge Of the Sith. Think a fiery spring glacier flood with lots of debris in it, spreading out. The edges of the advancing lava flows at Pillan would perhaps resemble large masses of slabby pahoehoe or even Aa digging into thick layers of sulfur snow, behind that is a faster moving jumbly mass, with more speed and fluidity the further behind the flow fronts you go. Most of the lava surface had a jumbly flexible crust. Fast moving lava flows spreading out over 1000 s of square kilometers is an impressive thought, such an eruption on Earth would form massive pyrocumulus and dramatic skies because of rising heat, but in Io’s vacuum that does not happen, but it would still be an incredible sight. The lava flows would move forward with spectacular volatile-rich explosions raging through them.

Gas buildup from ices (all volcanic gases on Io, which is as cold as hell, tend to snow out and settle as snow), can cause these plates and raft textures and swollen forms to form in the flow field, like the one seen below and to the left of the dark pit on the close-up photo of the lava flows. The lava flow field also have large slabs of crust indeed suggestive of fast emplacement with the high lava effusion rate would lead to a crumpling of the lava crust as the flow front likely Aa lava advanced at a speed of 1 kilometer per day, the result of the leading edge giving up heat to vaporize surface snow. This could perhaps create the rubbly surface texture found in the October 1999 images together with the fast eruption rates. Some suspected a komatiitic composition because of Galileo’s remote temperature measurements and the lower viscosity than that of the most mafic lavas that form inflated pahoehoe flows. Some think that it is just this combination of different eruptive and rheologic characteristics produced the unfamiliar surface lava morphology that was seen at Pillan. The original assumptions was made, in the year 2000 by Nasa geologists, that the presence of what appear to be rafted plates of rock on the upper flow surface suggests rapid lava surges or turbulence variations in a turbulence flow emplacement, they assumed Pillan lavas were low-viscosity, perhaps ultrabasic silicates because of that as the viewed the Galileo data. Another interesting point is that the apparent flows are wide, thin sheet flows rather than channelized flows which strongly suggests fast eruption rates. But sheet-like flows with a strange surface morphology fed by lava channels have been found in ancient terrestrial komatiite flow outcrops in Western Australia although they lack rough upper surfaces. The channelization of lava would be expected over rough topography, although there is not currently not a good close-up resolution of the pre-eruption ground substrate. As told earlier another explanation for the strange flow surface morphology is that it might be due to fragmentation of the flow by degassing or disruption of the lava flow by explosive interaction with the Ionian sulfur snow or icy substrate rather than a komatiitic composition. But it is also true that a very hot basalt will also be incredibly fluid and there are similar lava features on Mars.

When the Galileo Spacecraft looked at the eruption from a far distance with its SSI/NIMS temperature instrument, data collected for the 1997 Pillan eruption showed temperatures of 1590 degrees C. This value is close to the estimated eruption temperatures of a Commondale komatiite/Io analog composition, which was calculated by geologists to erupted at 1611 C using the igneous petrology program MELTS. The identification of orthopyroxene minerals in the Pillan lava flows and the fact that that most magmas erupt below full liquid temperatures (in which the two- temperature-area model fit provides only a lower limit on magmas liquidus temperature), some astronomers and geologists thought that the Commondale composition is a useful analog for Pillan. We can evaluate flow emplacement with this composition for the range of eruption temperatures consistent with Galileo data. The average thickness of the 1997 Pillan lava flows is 9 meters. Assuming that these values are typical of the Pillan lava flows, they may seem too thick for komatiitic flows and flows of temperatures over 1350 C. But long flakes of olivine crystals may cause some komatiitic flows on Io to appear thicker than they are. In recent data analysis from the Galileo Mothership the suspected komatiitic temperatures have been questioned due to inaccurate ways to understand and process the data from the Galileo Spacecraft, and the instruments on Galileo were not ultra-specialized for study of ionian eruptions. Today temperatures of around 1320 degrees C are generally more accepted for Ionian outburst eruptions as they over-saturated the instruments that Galileo had. Some readings where so high (1900 C) that they came into problems with how much tidal heating is possible at current situation. But still 1320 C is at the upper end of normal basaltic temperatures and borders on ultramafic eruption temperatures, Ionian magmas may be analogous to lunar mare basalt that are also thought to be hotter than most typical basalts on earth, but cooler than komatiites. But in all because of low resolution of thermal data and different ways to study them, ultramafic temperatures are not completely ruled out for the Pillan eruption, but the thickness of the lava flow fronts may suggest basalt rather than Komatiite. Still the viscosity was very low for these lavas, as low as Halema’uma’u and Nyiragongo, perhaps much lower still lava flows also thickens up as it cools when it leaves the vent. On Io s frozen surface the hot lava will bleed of heat into the cold icy surface of Io as it flows over causing mineral crystals to form in the lava, these mineral crystals increase viscosity. Thoelitic Basalt fits well in the data sets, as possible higher temperatures is not necessary to explain the instrument data.

Covering around 5600 square kilometers of Ionian ground outside Pillan Patera, with a 10 to 11 meter thick lava flow requires around 56 km3 of lava erupted, a volume beyond any recent historical eruption on Earth, and that is just what was emplaced outside Pillan ”caldera”. Most of the lava volume flowed into the caldera, over the years when the event where going, so the volume that was erupted as a whole could be twice as large, giving 112 km3 erupted by Pillan 1997. We don’t know how much erupted as we lack high resolution imagery of the lava levels in the caldera, before and after. Since Pillan Patera is 70 kilometers wide and 3 km deep, that allows eruptions of many 1000s of km3 to happen without covering much ionian lands surface, as much of the lava would flow into Pillan’s caldera and become trapped there. The amounts of lava erupted by the 1997 eruption is unknown because of this, but up to 75 – 140 km3 is maybe possible, it depends on eruption rates and how long those lasted. It is worth to remember that 1 km3 is around the volume of the entire Leilani eruption, so the event is much larger than any modern human historical lava flow here on Earth. Laki was 15 km3 so much smaller too. But Earth’s largest flood basalts can have some individual lava flows that reach over 10,000 km3, far larger than Pillan. It seems that Pillan’s flows where something between Mauna Loa, Laki and Siberian Traps in scale in terms of eruptions on Earth, far larger than for example Holuhraun and Laki, but far smaller than LIP flows on Earth. It is important to note that Io has gigantic lava channels like the old Twhaki Vallis, that may suggest that Io too is capable of LIP scale (VEI 8 by volume) flows. In addition to the lava flows, the 140-km-high plume eruption that deposited dark, orthopyroxene-rich pyroclastic material over 125,000 square kilometers also yields many of additional cubic kilometers of basalt erupted from this extraterrestrial eruption. On Earth the 1997 event would be a severe eruption and cause severe local gas pollution and some global weather effects and frequent eruptions of Ionian scale and frequency would degrade the global environment. In short because Pillan’s lava flowed down into Pillan Patera and collected there the real eruption volume is probably much larger than old conservative estimates. The eruption lasted for years at slower pace meaning even more unknown lava volume. The eruption at Pillan gained quite a lot of attention from researchers in planetary sciences, volcanology, remote sensing and geology and perhaps can be seen as the firework celebration for the future golden age of galilean satellite geology studies and exploration.

The lava falls at Pillan Patera

Art by Justinas Vitkus specialy painted for myself after I asked him by email, Justv23 is a very talented space artist. This showing the lava cascading into Pillan Patera forming 3 kilometers tall lava falls, exactly what was seen in the Galileo data. Click on image for full resolution.

With many 10s of km3 of basalt being pumped out just north of Pillan Patera, there was no doubt it would flow into it and that is exactly what Galileo Spacecraft saw as it was flooded by dark lava when photos of the caldera was compared before and after 1997. The filling of Pillan Pateras floor formed the largest and tallest lava falls that have ever been observed. That is the reason I wanted to talk about this eruption because it would be an incredible sight to be there when it happened. Lava flows filling pit craters, forming lava falls, are common on Earth. The 1969 Mauna Ulu lava falls are the most famous example. When fast moving fluid lava from Mauna Ulu arrived at ‘Alae pit crater at 11 p.m. on August 5, 1969, the lava flows crashed into it. The Mauna Ulu lava falls were taller than Niagara falls at well over 150 meters and they were over 300 m wide in some areas. Another much more extraordinary example of lava falls and the largest case seen by cameras on Earth so far was Sierra Negra in 2005. The 2005 eruption erupted along its caldera wall and formed a 3 to 4 kilometers wide lava fall clearly seen in this video, and is the largest lava fall caught on Earth so far, that event can only be found in three youtube videos.

But the filling of Pillan Patera’s floor which is 70 km wide and surrounded by 3 kilometers high pit walls means a much grander sight than Mauna Ulu or Sierra Negra for sure. It was during the first weeks of the eruption at Pillan when lava output was at its most intense and the lava falls most spectacular. The lava flows plunged into Pillan at three places, with each lava fall at least at the start 23 kilometers wide and a mind-boggling 3000 meters tall. The scene would be most spectacular at the start when large sheet flows from the fissure eruption plunged into the abyss, a little like when massive sheet aa, or flood pahoehoe emerges from fast fissures on Earth, creating lava falls almost as wide as the caldera itself. Later on the diminishing eruption would feed smaller but still intense lava falls into the pit. At their max the three Ionian 1997 lava falls would have been 3 to 4 times wider than the entire Sierra Negras caldera itself and the falls perhaps as tall as Etna. To put this in other scales, lava falls filling of pit crater floors at Kilauea involve craters a few hundreds meters to over a kilometer wide, while the Pillan Patera event was a pit crater the size of Reunion Island, dwarfing the terrestrial examples.

The lava falls at Pillan when most intense would far exceed any known lava fall on Earth in size and speed with many 10s of Leilani volumes going over the edge in perhaps a matter of days falling kilometers down. The lava covered the 2500 square kilometer floor of Pillan rather quickly, so the lava must have been very hot and fluid to avoid from cooling much and the enormous eruption rates help to kept it liquid as it fell into the ”Pillan’s caldera”. Io’s vacuum also helped to keep the lava liquid as it can only cool by radiation. In other words the falling curtains of liquid stone heated itself and allowed the lava to fall 3 km without cooling much, so it could rapidly flood the 2500 square kilometers floor of Pillan Patera without clogging up and gaining viscosity.

Just by looking at surface are Pillan’s floor has, we can understand the scale of it. The 2014 holuhraun lava flow field is about 84 square kilometers, here Pillan’s floor is 2500 square kilometers, far far larger than even Eldgja’s 780 square kilometers. Pillan Patera being basically a ”caldera pit” can accommodate a lot of lava without taking up more Ionian surface so a lot of lava from the eruption ended up here as I mentioned above. The lava falls would be an extraordinary sight, as the lava vent over the edge it would first fall slower than on Earth but picking up speed, huge clouds of dark pyroclasts would surround these immense glowing lava falls, a little like waterfall spray, forming huge curtains of black droplets that fall down,.Large amounts of heat and light are also released, so the falls would perhaps resemble a huge mix of burning oil and liquid iron slag, that is the best analogue of something of this scale. Large lava fountains on Earth form such falling ejecta curtains, and these may be formed in a massive lava fall as well. They were literal dam bursts, walls of lava falls going on for miles and kilometers deep. It is kind of difficult to imagine the scale of the lava falls at Pillan and exactly what it may have looked like. A visitor in radiation proof futuristic suit, would still have to see the spectacle from far ahead to avoid being overheated by thermal radiation. Think it as if large areas of the Grand Canyon began to fill with liquid iron, that is the scale of Pillan Patera’s lava falls. There have been lava falls in the Grand Canyon as recent as the Pleistocene, but the Ionian events at Pillan dwarfs them.

The lava falls could have either be single 3000 m high or be terraced into many huge falls over each other. That depends how Pillan’s walls are structured, but whatever is the correct picture, they where huge as Pillan’s walls are very steep so you gets an enormous flow rate from that, at these huge scales as well the lava flowed more like water than liquid rock, and the real viscosity was probably lower than earthly basalts. The lava falls also exposed large amounts of hot surface giving large amounts of thermal radiation, in other words Pillan lit up strongly and oversaturated Galileo’s sensors. Neither the lava falls or active lava flows were observed in close details by Galileo Spacecraft who did close-up photography, just after the eruption was in max phase. After the eruption and filling of Pillan’s floor the lava flows turned green as the hot basalt degassed and reacted with falling sulfur from other volcanic vents.

More strong thermal Ionian outbursts eruptions around Pillan Patera and Pillan Mons occured in the year 2007, in 2008 , March 8 in 2015, March 31 in 2015, May 5 in 2015 and February 18 in 2015. These events like the summer 1997 also produced spectacular lava flows as there is no doubt they too flowed into Pillan Patera forming incredible lava falls as well. It’s very likely that in the far future that Pillan Patera maybe completely filled by lava flows. Filling of Ionian volcanic depressions (pateras) are likely a very common occurrence on Io, either from fissure eruptions flowing in as lava falls or eruptions inside it filling the floors. The patera floor of Pillan have layers of basaltic flows from numerous earlier eruptions. The March 2015 eruption had a fissure that pierced the patera wall as thermal radiation came from there, unlike the 1997 event that erupted nearby at Pillan Mons. None of the later thermal outbursts were observed by space probes in orbit around Jupiter. The immense Ionian lava falls at Pillan Patera have been overlooked, so I felt I needed to write about them, to further increase their ”famousity” and awareness among geologists.

I asked Justv23 to paint them for me as well, so I could put it in an article for VC. As spectacular as the lava falls at Pillan patera were, they were like the Kraffts used to say about most eruptions, an amazing theater show playing in front of an empty public, with only the brooding Jupiter looking on.

Art: by Myself, modified a NASA graphic to make a quick sketch of the Pillan event.

Art by Lucasfilm: The lava falls at Mustafar are not far off what it would be like to see the lava flows cascade into Pillan’s pit. With many 10s of km3 of lava falling over the much more than the Grand Canyon deep pit walls, it would be an Impressive sight far surpassing the 2005 Sierra Negra event.

The Sierra Negra 2005 eruption was the largest lava falls ever seen on Earth by cameras. Using them and scaling them up, we can give some sense of the massive scale of the Pillan event with placed Ionian scales here for the 1997 eruption. In real life the scale is 10 km wide for sierra negras caldera and lava tongue is a few km wide at max. The Galapagos lava falls in 2005 was max a few 100’s m high. The pillan Jupiter eruption dwarfed it. Video sources for photo: top and bottom.


I have known since 10 years old that Io has volcanoes, but actually that a volcanic event on this grand scale was captured is just astonishing and really shows how Ionian eruptions can dwarf any recent historical events on Earth. In other words, the geologically activity on Io is off the scales when it comes to Earth’s currently active volcanoes. Even more cool and astonishing is that it was seen by a little machine that man sent there, a billion kilometers from Earth. The 1997 Pillan Patera are by far the largest lava falls that have ever been seen. With multiple 10’s of cubic kilometers of erupted lava it is the largest basaltic eruption caught that has been recorded by instruments so far, with perhaps more than half of that ending up in the caldera. (But very possible there have been much larger Ionian eruptions from other long lived recorded thermal outbursts.) I plan other articles on Ionian volcanoes later as well. The lava falls at Pillan is the most spectacular volcanic event that has ever been recorded in action by remote sensors, far exceeding in my option 2022 the Tonga event. In other worlds on Io we can observe volcanic activity that would be catastrophic on Earth and large eruption processes that only happens perhaps once every 100 000s of years on Earth. Some of Io’s largest volcanoes may have never existed on Earth since the Hadean era, like the huge lava sea of Loki Patera. Large scale volcanic activity on Io gives an insight to old ancient eruptions on Earth and therefore is of tremendous interest to planetary geologists to understand our own planet. Some geologists think that the Columbia River Basalt Flows CRB sequences are quite analogous to Pillan Pateras lava flows, as they share many of their suggested morphologies as inflated ”flood sheet pahoehoes” and indeed perhaps Pillan was a LIP scale flow on Earth in terms of eruption rates, But perhaps not like true LIP flows in size.

Also huge thanks to JustV23, Justinas Vitkus for painting the 1997’s lava falls event for me, as he is a very skilled self taught space artist for sure and is likely going to do more Io artwork for me later. The lava falls at Pillan Patera haves to be the volcanic event of the century, because how spectacular it was. A surprising amount can be learned from the few photos and measurements that was taken from the Pillan eruption. And really shows the value of cameras and remote sensing when humans cannot go in person. Because Io is the most volcanically active body in the solar system, I constantly daydream about it, the thought of huge lava fountains blazing in front of the looming Jupiter is an unreal sight. In 2003 the Galileo probe was getting sick from jovian radiation its instruments began to fail, and the high command at JPL de-orbited the probe, burning up in Jupiter’s atmosphere at insane speeds.
In February 2024 Juno Spacecraft will come as close to Io as 1500 kilometers and we should get some good close-up imagery, seeing over 20 years of change on the solar systems most geologically active object.

Photo Galileo Spacecraft, this is the best distant photography taken in 1997 of the Pillan eruption.

Jesper Sandberg, May 2023


This article written in my own words and explanations is based very much on Ashley Davies and Rosaly Lopes works on Io and their books ”Volcanism on Io a comparison with Earth” and ” Io after Galileo, a New view of Jupiter’s Moon”.  Dr Davies is a volcanologist at Nasa JPL who did a lot of complicated work on Galileo’s thermal data from Ionian eruptions and worked out mathematical models for these data streams. Dr Rosaly Lopes is a planetary geologist, volcanologist who has named many of Io’s volcanoes and found many earlier unknown Ionian volcanoes as well. Everything is based on my own thoughts of the eruption and what I finds interesting. Neither Davies or Lopes et al talks much at all about the gigantic lava falls, that was the highlight of the Pillan eruption, so that is why I wrote about them.’s_thermal_emission_from_the_Galileo_photopolarimeter-radiometer

A post-Galileo view of Io’s interior – Zenodo

New estimates for Io eruption temperatures – Zenodo

131 thoughts on “Io’s Pillan Patera eruption in 1997: the largest lava falls ever seen

  1. A New article from Myself is up on Volcanocafe! Its time to talk about a geological event on one of Jupiters Moons that only I and a handfull of persons on the entire planet knows about !

  2. Pillan eruption must have been a spectacular sight indeed. Hahaha but for me mostly one thing comes to mind thinking about Io and that is Mustafar

    ( John Williams music )

    A helpless Anakin lys beside the raging lava rivers at Pillan on Io, enraged he stares at his former master Obi Wan that defeated him

    Obi Wan looks at Anakin in huge
    dissapointment –

    Obi Wan screams out
    You were the Chosen One!,
    It was said that you would destroy the Sith, not joining them!!…bring balance to the Force, not leave it in darkness!!

    Anakin that fallen to the dark
    side screams out to Obi Wan I HATE YOU!!! twisting in pain ..

    Obi Wan slowly walking away from the lava rivers edge while Jupiter looms in the sky, he takes away Anakins lightsaber causing a rage in the already angry Sith apprentice.
    The intense heat of the lava will soon seal skywalkers fate, as he catch fire, first the clothes then the skin, soon you dont see him anymore just a pillar of fire that have something in it. Obi Wan walks away in horror.

    An hour later using the power of the dark side, skywalker manage to stay alive, and the inferno around him stop, he pulls his way from the raging lava rivers edge severely charred. Darth Sidious / Palpatine his new master feels Anakin is in trouble on Io and flys there togther with a patrol.

    ( Stromtroopers searching Io s surface togther with Palaptine ) .. looking across the raging landscape they see a burned shape. Stormtrooper Clone ..Your Majesty this way!!! Palpatine sees the charred shape thats his Sith apprentice .. Palpatine should there he is! .. and he is still alive.. Palpy shouts out – send a medical capulse instantly! .. the clones – yes sirr!

    Its Impossible for me to not think of the Revenge Of The Sith when I think of Io
    So Io Will always be the Mustafar for me 🙂
    And Mustafars volcanism is also caused by the tidal thug of Gas Giants so very similar to Io. I guess Io inspired George Lucas

  3. The lava falls would have impacted the floor of the caldera at 370 km/hr, probably less in reality as the wall isnt goign to be vertical, but still falling from such a great height even in the lower gravity on Io, it would have been insanely fast, a lot faster than the lava would have flowed there and how fast lava can probably fall on Earth, there is no terminal velocity in a vacuum 🙂

    Io has gravity of 1.8 m/s2, it is about 1/5 of our gravity, and a little higher than on the Moon (1.6m/s2). It is also the highest of all moons, actually, probably befitting the fact that it and our Moon are both silicate objects, while most other moons are more icy, and less dense. No moon is close to the planets though, Mercury and Mars are both 3.7 m/s2, Jupiter is a massive 24.9 m/s2, if lava could fall 3 km on something with the gravity of Jupiter it would hit the ground at 1300 km/hr, although a 3 km cliff wouldnt form in that environment 🙂

    • And the sun is 274 m/s2, just to orbit the sun at 1000 km above its surface you need to move at 40 million km/hr 😀

      • Thats why impact events on the Sun release a terrible ammounts of energy

    • The radiation proof suited astronaut both crushed and burned at the same time D :

  4. Io is one Moon we will never call home
    Crazy volcanism and insane radiation

  5. Jason Perrys Io blog is very useful for information on Io, one of the best sources of Ionian information on the web and gave alot of inspiration for me togther with the limited book litterature that exist. Always cite sources of course

  6. A well needed article is this, as the lava falls is an event that very very few knows of so have fun reading

  7. It is a fascinating event. It is a good thing our volcanoes aren’t like this! Our atmosphere is too fragile to cope with this

    • Earth woud turn to Venus as I guess with souch level of activity as standard ?

      This event Dwarfs Holuhraun and Leilani really and some Ionian eruptions Dwarfs Pillan eruption

      Yes really really scary basaltic volcanism

    • Fascination indeed! Io sounds nightmarish.. the whole sky gets lit by lava fountains and these lava falls.. so Big that woud be a perfect place for Sauron

      Mordor Moon really! These lava falls .. difficult to grasp or even describe the scale of that 🙂 the Moon should be called Vulcan

    • 2001 eruption makes Pillan look like a fart

      Yes Io have some really bad volcanism indeed .. on Earth it woud be bad news

    • On Io basaltic lava flows, sulfur Ice, and pyroclastic materials builds up into a somekind of pancake that just gets deeper and deeper until the whole mix gets buried deep enough To melt and gets recycled into the inner magma ocean 40 to 60 km down. Very difftent from Earths crust, Io is a very primitive world

    • Just imagine If this happened at Fagradalshraun ( Eeeeeek ) luckly not possible there, still some of Icelands larger earlier lava flows 11 million years ago ( just may have been in the many 10 s of km3 range ) and some unknown Hawaiian flows as well

      But I still think Ionian lava flows like these are far worse than any non LIP flows on Earth, and specialy so for the 2001 Ionian event that was 100 times more powerful than Pillan! ( mind boggles ) and these Maybe even exceeding terestrial LIP vents for the Ionian 1991 and 2001 vents

    • Pillan 1997 have an unkown volume since alot flowed into the Patera and collected there, its not Impossible its a well over 100 km3 event

  8. Nice, makes the Alae lava falls look cute!

    The size of Pillan is incredible, 70 kilometres in diameter must make it bigger than Toba, and 3 kilometres tall. And there are even bigger and deeper paterae in Io. Now add the lava falls to get the perfect show.

    That artwork by Justinas Vitkus is impressive, and the choice to paint the walls yellow is interesting. The same choice I would have made. The other choice would be to paint them black, with stratified lava flows. This depiction would show paterae to be erosional features in a sulphur/sulphur dioxide ice crust rather than collapse features of a large shield volcano.

    • The Patera walls coud vary, on location, some like Chaac-Camaxtli region have calderas with features both of basalt erosion in ”sulfur glaciers” and features of collapse pits with magma withdrawl.

      Chaach Patera have dark walls suggesting sillicate basalt magma withdrawl rather than being eroded by hot basalt in a sulfur icesheet. Chaach does have sillicate pahoehoe flows in it and sillicate basalt lava flows are probaly eating away at the ”Sulfur Ice Walls” lava lakes like Loki Patera are also probaly eating away at the cold volatile rich surface

      Other Ionian calderas do appear that the hot basalt have competely carved a hole in a sulfur icecap, souch example coud be
      Balder Patera and Ababinili Patera. Souch Pateras may even have pure So2 flows and not only basalt as the hot rising silicate lava melts the So2 Ice

      Ios outer surface crust consists of a weak mix of basalt lava flows, pyroclastic materials and sulfur snow Ice and countless dykes and intrusions of basalt. Its probaly lots more volatile So2 icey rich than any of Earths crusts. Sulfur glaciers seems possible as well with the constant snowfall of sulfur from other basaltic vents

      • Lava-sulphur interaction must be a huge part of Ionian eruptions. Sulphur must have exploded everywhere the Pillan lava flow touched.

      • Yes and that was seen in Thor eruption too fast, very fast lava flows like these means even far more violent sulfur Ice and basalt lava flow interaction than in the slow tube feed prometheous flows

      • The walls of Chaac Patera that were photographed are nested within another larger patera, so they probably expose the lava filling of that larger patera. I wish we had better maps of Ionian volcanoes. Maps! Unlimited Maps! must I have.

    • In some places on Io like Prometheous and Amirani basaltic pahoehoe flows are digging through thin layers of so2 Ice and you gets surface lava flows

      Some other areas on Io have much thicker sO2 icecap and you gets pit craters that are digged out by basaltic lavas and lava lakes instead, I wonder If carving by basalt coud be stopped If it hits a basalt dyke like a wall in the Ice 🙂

      • The very tall non volcanic Mountains that can be found on Io strongly suggest a sillicate rich crust, but of course the outer crust is probaly a weak layer of sulfur snow, pyroclastic materials, and basaltic lava flows and countless intrusions. So Io s outer surface is mechanicaly weak and low in density

        The crust composition likey gets more Sio2 rich as you descends down into it. There Maybe even liquid sulfur aquifers at depth, heated by active sillicate magma chambers

      • Anyway the 1997 eruption proved that Io does indeed erupt sillicate basalt lava maybe even ultramafic lava and that sillicate mafic lavas are the dominant type of volcanism even If sulfur gas volatiles still plays a huge role as magmatic volatile

    • Io s Chaac Patera thats 50 kilometers long, have many features of terestrial basaltic volcanism souch as inflation mounds tumulus and humocky pahoehoe and lava layers in caldera walls, But the scale is off any terestrial basaltic calderas. The low magmatic bouyancy at Io with its lower gravity must play a part of doing oversized volcanoes and eruptions compared to Earths daily avarge and is probaly why Ionian volcanoes seems so strange compared to terestrial ones. Chaach s walls height are more than Half the diameter of Kilaueas caldera, Infact I doubt Earth never gets these scales of features in its basaltic volcanism. The Green color is pyrite frost as sulfur snow settle on hot basalt

      • More like 150 km long huge feature compared To any earthly volcanic features and is quite marsian in scale and far more active than any marsian volcano

  9. Brilliant article Jesper!

    I’ll have to read it a few times over to absorb all the information.
    The scale of the lava falls is astonishing. The picture by JustV23 is wonderful.

    I’m still processing the information that because of the vacuum of space the lava doesn’t cool down.

    *its been ages since I posted so this will probably go to the dungeon.

    • Fun you enjoyed it : ) yes It cools but much slower than in Earths atmosphere, still Pillans flows defentivly had a dark crustal ”scum” on it as it raged over the landscape But probaly alot more incandence than on Earth further from the vents it woud have rafts of crust in the fiery flow

      The scale of these lava falls are indeed beyond insanity

  10. Tidal stirring…
    Volcanoes may carpet surface of newfound Earth-size exoplanet
    The exoplanet, known as LP 791-18 d, orbits a red dwarf star about 90 light-years from Earth, in the southern constellation Crater. It’s slightly larger and more massive than Earth, according to the study team — and it’s probably much more volcanically active than our planet.

    “LP 791-18 d is tidally locked, which means the same side constantly faces its star,” co-author Björn Benneke, an astronomy professor at the University of Montreal’s Institute for Research on Exoplanets who planned and supervised the study, said in a statement.
    One of the other planets in this tight system gets close enough for tidal stirring…

  11. Yesterday/today Popocatepetl has been producing explosions in rapid succession. Which seems very intense for Popocatepetl, don’t know if this has happened before. This is actually a bit ominous in a volcano that can go fully plinian on an Agung level. A plinian eruption happens when the upward flow in the conduit speeds up to the point of effusion being continuous, what we are seeing is that magma is rising up faster and faster, making more frequent explosions, building inertia, we will see where it leads (might not really go anywhere though). Live stream, there is fog and rain unfortunately:

    • Just took a look now and there looks to be a continuous column and noise, not separate explosions. Does this count as a Plinian eruption?

      • There is a continuous, glowing lava fountain right now that the clouds have cleared, a bit Etna-like, so I guess it’s subplinian at least. So yes, magma is continuously rising up and fragmentating. It’s not as intense as I thought it would be, although the eruption might still be ramping up, so who knows.

        • I think it’s much stronger right now than yesterday. The lava fountain is continuously sending lava over the rim of the crater, and the plume is much wider. There is a risk of pyroclastic flows if all that spatter collapses.

          • I wonder if a batch of more fluid magma has started erupting, not necessarily a different composition,but it isnt really that explosive, it is only a lava fountain.

            Some of the lava domes I have seen pictures of at Popocatepetl seem to be quite sticky, but perhaps that was just some cooled stuff, and the hotter magma is more fluid. After seeing how fluid the dacite at Aniakchak is it is pretty clear that high silica magma can flow easily if it is hot or lower in crystals. I guess, most glass formulas are as more silicic than rhyolite but flow easily. Certainly Popocatepetl isnt the same sort of volcano as Shevluch or Merapi anyway.

          • Maybe a lava dome is simply rising up rapidly in the crater, growing bubbles and jetting gas, continuously spraying ash and lava, but still mostly effusive.

          • More what I meabt is pictures I have seen before of domes at Popocatepetl look more explosive, and actually typically have been, but this time around has been a lava fountain. The fountain really is a fountain too not just hot rock, when the livestream tyrned off night mode it was visible glowing orange in the dawn light, so is probably upwards of 1000 C or more, hot for a dacite. Probably would closely resemble the domes at Semeru, which us basically the same, sticky but still mobile lava, not viscous enough to make domes.

            Popocatepetl has had an open conduit and prolific CO2 emissions for decades, probably there is a great deal of magma connected to it at depth. So makes sense if the stuff it erupts is not as viscous as its older neighbors to the north.

          • I’ve been watching Popo the last couple days, too.
            Some loud explosions last night and a continuous roar, some lava bombs.
            It is still going right now.
            Yesterday the lava bombs were going up pretty high (count in seconds how long to land maybe 3-5)

      • Souch fluid domes are called ”pancake domes” and are really ponded blocky lava flows rather than real domes

  12. A high professionell work on (dwarf) planet “Vulcan” of our Solar system, the home of volcanoes!

    Interesting for me is that the chemistry of Io’s magma is basaltic, very close to Earth. That’s not naturally to have the same planetary chemical composition as on Earth over such a long distance with different distance to Sun and gravity by Jupiter.
    How would Io look like as Earth’s moon? Earth also has some gravity tidal impact on Moon, but of course it’s much weaker. In the first millenia of Moon’s existence, when it was still a lot liquid inside, it may also have had some gravital volcanism like Io now. There still exist moonquakes which are caused by Earth’s gravity force on Moon, which is 20 times higher than the force of Moon on Earth.
    Volcanism on Io is likely driven by interaction between Io’s intra planetary dynamics and Jupiter’s gravity. What circumstances let the event of 1997 happen?

    • Its something similar to basalt clearly a hot sillicate melt. Io formed in its own jovian subnebula so Ionian rocks maybe have a mafic chemistry somewhat difftent from Earths basalts. But all planets formed from the same solar nebula stuff leading to about similar basaltic lava flows on all bodies. Infact something akind basalts are probaly the norm on exoplanets as well

      Ionian magmas at least some of them coud be Komatites too

    • 1997 was gas overpressure from a deep magma chamber likley and been many eruptions there since then. Pillan like most of Io s volcanoes are absoutley monsterious compared to any induvidual volcanoes on Earth.

      Some Ionian volcanoes may have a deep base supply of many 100 s of cubic meters a second

    • Many 1000 s of cubic meters a second is not Impossible as deep supply for Pillan during its most frequent eruption years .. But a deep supply of a few 100 s of cubic meters a second is more realistic and thats Absoutley enormous number

      • While the absolute size of Io’s eruptions already are impressive, they are even more gigantic in relation to Io’s volume. Io has a diameter of around 1/3 to 1/4 of earth. So Earth has at least a volume of 108 times Io. An eruption with 1km³ on Io is like more than 100km³ on Earth in relation to volume.

        • Some Ionian eruptions with scale scale on Earth woud be VEI 8 I guess according to plume fallout size that can be 1000 s of km wide on Io in some cases

        • The Moon is 2% of the volume of the Earth, which is 1/50. Io is a bit bigger than the Moon, so it is a lot more than 1/100 as big, probably more like 1/40, So a 1 km3 volume there is more equivalent to 30-50 km3.

          But that doesnt really change things much 🙂

          By this analogy the 1997 eruption was equivalent to an eruption of at least 2300 km3 of lava on Earth, to get a comparable scale. The 2015 eruption was probably equivalent to a VEI 9, although as it was not explosive this isnt the best metric. But it was really something, a basaltic Toba, basically. Will need to find how big the Surt eruption in 2001 was, it might not have been so big in volume just extremely intense, maybe a functional equivalent to an ignimbrite but in a vacuum it would still be effusive.

        • To give some numbers, the tidal heat in Io amounts to something like 2.25 W m^-2 of surface area. On Earth, it is 0.005 W m^-2. However, it is not quite as bas this since the Earth has other internal heat sources: radio activity, left-over heat from the past, latent heat from the solidification of the core and a bit from core contraction. In total that gives 0.09 W m^-2. So Io still wins by a factor of 25. We know the heat budget from Io quite well, but it is possible that tidal heating is a bit less and other heat sources (radio activity) has sone contribution. But this explains in part why Io is magma-productive. It also depends on the temperature and pressure inside and how this compares to the melting point. And there is some self-regulation: molten material transports heat much better, so if there is a lot of mama it helps to keep the inside a bit cooler.

      • Is Io s core completely liquid? It does not have its own magnetosphere

        The mantle is hard to say and only the uppermost mantle Maybe a magma ocean

        • Not known but it is likely that the core (whether fully or partially iron) is liquid.

    • Yes they should rename Io ”vulcan” fits well for its fiery nature

      • The name ‘vulcan’ has been taken. Admittedly for a planet we now know doesn’t exist, but it should not be used for two different planets!

    • still occasionally booming at 12:15 utc ,, am i seeing dust clouds from debris /ejecta impacts also

  13. As daunting as it was to land probes on the surface of Venus, yet eight times it was done, the first times using 1969 technology. I wonder what a probe similar to Mars InSight could tell us about Io. I wonder what more we could learn about the dynamics of the magma “ocean” beneath the crust and how orbital period and thermodynamics affects its motions as well as does tidal kneading.

    • Yes thats what I wants too Infact I wants an Io curiousity style rover that coud be landed near the dark sillicate eruption centers and drive around and do photography and petrology, basicaly a ”robo volcanologist”. The radiation protection for that exist, althrough its a very harsh enviroment.

      Since communications are not in real time, driving around inside an active flow field like prometheous on Io may not be possible without the rover being swallowed by lava breakouts.

      So exploration of lava lakes and caldera rims maybe more realistic for a surface Io rover, where it can drive around ( If an eruption does not happen ). Pele Patera and Chaach coud be very good landing spots, specialy at the mountain plateau of Danube Planum overlooking peles lava lake. Driving around in the sulfur deserts between the basalt eruption centers woud be safest, althrough woud be very boring. In February 2024 Juno will come very close to Io and hopefuly we will get good Photos

        • Even in those pictures the glowing volcanoes are visible on the night side 🙂

          Also a massive black area, what I presume is the lava lake at Loki.

          • This is the description from the junocam site,

            On May 16, 2023, Juno passed within 35,000 kilometers of Io’s surface. JunoCAM acquired these eight views over a period of an hour and fifteen minutes as the spacecraft approached and receded from Jupiter’s volcanic moon. These are the sharpest visible-light images of Io acquired since the New Horizons flew past Jupiter on its way to Pluto in 2007. They reveal a landscape of mountains and volcanoes, some revealing changes over the course of sixteen years and others revealed due to the unique lighting and viewing geometry of Juno’s flybys.

            Several surface changes are visible compared to images taken by New Horizons sixteen years ago and Galileo more than twenty years ago. Some were seen in previous Juno encounters such as fresh red material surrounding Chors Patera and a darkening at a volcano east of Girru Patera. Revealed for the first time in these images are changes at the volcano Volund. Thermal data from the JIRAM instrument, also onboard Juno, in previous encounters of Io showed two prominent areas of activity at Volund on its northwest end and to the west of a circular feature thought to be the vent area of Volund. Both these areas are now darker than they appeared in New Horizons LORRI images. These two dark areas are best seen as the upper two dark spots near the terminator (the boundary between day and night sides) in the middle of the third image from left in the top row. Images from encounters in July and October may help to reveal how these two changes are connected.

            The polar geometry of Juno’s encounters is helpful for mapping the terrain in Io’s north polar region. For example, a triangle patch of three bright regions, best seen above center in the second image from left in the bottom row, is revealed to be host to two mountains, one with a height of approximately 5 kilometers. Mountains in Io’s polar regions, like Haemus Montes, are often surrounded by moats of bright sulfur dioxide frost, and these two mountains appear similar. Confirmation of a third mountain will need to wait for imaging from the July and October encounters.

            The Io images show here have an original pixel scale of 24 to 52 kilometers per pixel and have been enlarged by 5x to improve the visibility of surface features.

      • February 2024 will be as close as 1500 kilometers from Io Hopes we gets good shots of lava flows and lava lakes

        If the probe is hardy enough is there enough fuel to put it into close orbit around Io? After the probes gets too radiation sick it coud be de – orbited into a lava lake by doing the maths when to do the correct burn

        • I wants more probes for Io!
          Not going to give up until Nasa makes one for us 😒

          Wants an ultra high res Io orbiter with Ice and titanium shielding .. Junocam will suck next year I guess

      • The Big lava flow of Lei Kung Fluctus is also visible in these recent Photos, looks very much the same since last time of the Galileo shots. Its the biggest recently emplaced pahoehoe flows in the solar system

        This is just one part of Io and will have been alot of more changes in 20 years since Galileo .. Jason Perry discuss the New surface changes that can be seen in this video

    • Sulfur snow and Ice is very common at Io as these gases freeze out from basalt erupting vents forming snow. There Maybe so much snow Ice that some Ionian eruptions are very much like eruptions in a sulfur glacier

      In other places the sulfur snow Ice is thinner and thin pahoehoe flows like prometheous are seen vaporizing the sulfur Ice as the hot lava flows over it. ( Photos ) Prometheous is clearly an active pahoehoe flow field as seen by numerous dark breakouts, the dark plumes are result of lava exploding into bits as it flows over sulfur Ice that cause gas explosions.

      And a paper

      • The lava exploding as it flows over the sulfur Ice is a good sign its hot mafic silicate lavas as well as the 1300 C readings from the Pillan eruption and the discovery of pyroxene materials

        Still Io s sulfur plains coud have older areas with km thick sulfur Ice ?

        • It is fun to think of such a hellish place as being glaciated, but really that is what it is, sulfur normally evaporates at 444 C, probably much less but still relatively high in a near vacuum, but this is still much less than lava temperature.

          Given that most volcanoes on Io seem to be relatively low output though, and stay active for a long time, the interaction probably is different than any observed subglacial eruption. Perhaps the formation of tuyas is similar though

          But rarer huge output lava floods like those in the past 30 years at Pillan, they probably do make violent interactions, both at the vent and on the flow. Based on the scale of thermal hotspots the eruption in 2015 was probably much larger than the 1997 eruption, it might well have been a full scale 1000 km3 LIP eruption. Perhaps very little of that area is untouched now.

          • It is something to think about how often these sorts of eruptions happen. Even at 500 m3/s rate of supply, which probably is on the higher side, it would take a good 75 years to get about 1000 km3 of magma. So depending on the size of the recent eruptions there might have been many decades or even centuries of low or no activity at Pillan. Which is similar to the highest numbers for some LIP traps formations that I have seen.

            Probably just like in Hawaii the volcanoes go through high and low periods of supply, potentially from 0 to 1000 m3/s. So there will be many obscured inactive volcanoes, and some that were active 20 years ago will be more quiet now.

            Lava lakes overturning are also extreme heat radiators, even without active overflow. Even glowing exposed lava flows dont compare, Halemaumau before 2018 was the most powerful single heat source on the planet going on as high as 1 gigawatt, which is equivalent to 20 GW/km2, an insane number really considering it was within a factor of 2 of this for most of a decade continuously. So the bright flares on Io need not necessarily be eruptions much bigger or even eruptions at all, just rapid lake overturning.

      • Yes the 2001 eruption was a 100 times more energy than the Pillan Eruption an absoutley astonishing eruption yes I do think the really large Ionian outbursts are analougus to LIP scale in terms of eruption output.

        Lucky it cannot happen in Iceland or Hawaii or Africa for now

      • The most intense thermal Ionian outbursts are lava fountains

        An overturning lava lake gives off alot of heat but the overturns are quite small, while the overturning front is huge ( long ) it takes weeks, many months for Loki Patera to resurface itself, still because of Lokis size 230 km wide lava lake it is Io s largest radiator and it seems that most Ionian thermal energy per day is lost through Giant lava lakes

        But a massive Fissure eruption like Pillan and Surt do release far more energy

  14. The situation in Popocatepetl is actually dangerous and life threatening. Lava bomb are continuously landing on the eastern side of the cone and building up, if those pyroclastic deposits collapse it might send pyroclastic flows east into San Nicolas de los Ranchos, San Juan Ocotepec, and other smaller villages, and they’ve barely just started evacuating.

    • Thank-fully the eruption has calmed a little. Spatter is no longer landing on the eastern flank in massive amounts like it was earlier.

  15. To put these lava falls into scale, each lava fall at Pillan was around 3 to 4 times wider than Manhattan is long and 3000 m high .. mind boggles really

    • Yes magnificent indeed right ?
      And yet some other Ionian eruptions been around 100 times more intense in energy… than Pillan

      What woud happen To Reykjavik If it happened in Brennsteinsfjöll? 😉

  16. Fascinating information!
    I wonder what will be the end game of the whole tidally locked Io – Europa – Ganymedes system?
    Will they slowly migrate towards larger orbits, but still in the same 1:2:4 resonance with each other?
    Hmm, just found a paper examining just this topic:

    G. Lari, M. Saillenfest, M. Fenucci, Long-term evolution of the Galilean satellites: the capture of Callisto into resonance, last revised 15 May 2020, in ArXiV:

    And how this will affect the amount of tidal pumping done on Io? And when the Sun leaves the main sequence, what happens then, are the moons just remelted, but stay on their orbits, or what? Can they keep the water vapor from escaping to the space?

    • Most of the mass of the Galilean moons are in rock, rather than Ice ocean layers. Europa, Ganymede and Calisto will remain as rocky Ice free balls after the sun becomes a white dwarf and tidal heating of Io will continue

    • That was the first Etna fountain of the hyperactive 2021 paroxysm years. The lava falls at Pillan Patera woud have looked perhaps very much like that a mess of lava spray falling down just that its 3000 m tall ! so simply mindblowing


    Eruption of Tonga underwater volcano found to disrupt satellite signals halfway around the world

    An international team has used satellite- and ground-based ionospheric observations to demonstrate that an air pressure wave triggered by volcanic eruptions could produce an equatorial plasma bubble (EPB) in the ionosphere, severely disrupting satellite-based communications. Their findings were published in the journal Scientific Reports.


    Some but not all Ionian eruptions maybe similar to subglacial eruptions on Earth If the basalt erupt under a thick sulfur icecap. It depends how thick the sulfur icecap is on Io s surface and that varies alot. In most volcanic eruption centers in Io like prometheous the sulfur Ice is quite thin or not just a meter or less as frequent hot eruptions vaporize any sulfur Ice. But all volcanic gases on Io does freeze out and have to be deposited elsewhere. In some of Io s older areas like the sulfur plains between the sillicate volcanism centers the sulfur Maybe kilometers thick? Souch an eruption there woud very much be like the Gjalp Eruption I guess but with sulfur instead of water Ice. Hot Ionian basalt and sulfur Ice will probaly form similar phenomena as to Gjalp.

    Large Ionian eruptions under sulfur icecaps Maybe even able to form a sulfur jökulhlaup? when the hot basalt melts large ammounts of sulfur Ice

    • For the Pillan eruption the sulfur Ice was probaly quite thin just a few m, Otherwise the basalt lava flows woud have digged wast pits in it. But it coud also be because of its low heat conductivity, that the lava may just glide over the sulfur Ice because of the ”leiden frost effect” gliding on a cool lower insulated chill base

      Still I think that the sulfur Ice on the surface was quite thin at Pillan area, But the shallow subsurface kilometer will have lots of sulfur Ice and older basaltic flows

      • Sulfur ‘ice’ is still going to be solid up to over 100 C, so unless near a lava flow it wont melt or evaporate, it will basically be a rock at the standard -150 on the surfaxe of Io. It us perhaps not impossible that some of the longer flow features are not silicate lava flows but sulfur flows though, although clearly there are long silicate lava flows too. Sulfur is a lot like oil as a liquid, more fluid than the lava, and has a wide fluid range. But that is all at 1 atmosphere, in a vacuum it might not stay a liquid very long at all, or could just sublimate anyway and never have a liquid stage. In that case then sulfur flows would be impossible unless Io forms a thicker atmosphere.

        I guess, the sulfur is just the result of billions of years of eruptions freezing out. Probably Io was more like the Moon now when it was young, and its present style might not actually be truely analogous to Hadean volcanism. The modern volcanoes are probably more explosive given the recycling of volatiles.

        • Neither sulfur nor sulfur dioxide can be liquid in vacuum. Pure sulfur (S8 molecules) can remain liquid down to 1.8×10^-5 bar (SO2 not lower than around 10^-3; it can barely exist in liquid form on Mars). Io has a listed surface pressure below 10^-10, too low for either to be liquid.

          • Remarkably, liquid sulfur could exist on … Pluto. If something kept it rather warmer than ambient. Pluto has a nitrogen atmosphere with a pressure of nearly 6×10^-5 bar, over three times the minimum for liquid S8.

          • That seems a bit high. The surface pressure of Pluto varies from 1.4 to 0.6 Pa, so around 10^-5 bar.

          • Makes sense, I wasnt sure where the triple point was and nothing easy to find had an answer… I assume though it will melt first under the lava, which is heavy and would allow pressure to go above the limit.

      • Hot shallow silicate magma chambers maybe able to melt large ammounts of buried sulfur Ice givning rise to sulfur aquifers. These sulfur chambers coud supply pure sulfur eruption fountains on the surface belching sulfur snow.

        But most If not entirely all volcanism on Io seems to be indeed basaltic as Galileo confirmed

    • All the volcanic gases on Io does freeze when it leaves the sillicate lava fountains and lakes, the Moon must have kilometers thick Ice deposits between active basaltic centers.

      Coud the subcrustal Ice layers of sulfur be criss crossed by basaltic dykes and laccoliths? woud be fun to drill in Io s outer crust on the older areas. The giant basalt lava sea that is Loki Patera seems to be eating its way through a volatile rich icey sourrounding and haves even icebergs floating in it

    • Albert woud it be easier to go close to lava flows on Io than on Earth? You have No superheated air to deal with close to the flows

      But a special space suit is needed

  19. I dont think PDC s exist on Io
    Pyroclastic flows are basicaly liquid turbulence currents in an atmospheric ocean, very similar to mud currents in water or milk in water or fire. Turbitidty currents are similar too. On Io there is No atmospheric pressure to keep a pyroclastic flow togther, in other words No fluid gas dynamics on Io. Still fallout from lava fountains maybe able to produce some similar deposits.
    If St Helens happened on Io it woud be orders of magnitude worse than on Earth! as gases expands so much more on Io s vaccum.. Not Held togther by atmospheric pressure. A pyroclastic flow on Io woud expand like crazy and disperse into space ( still Maybe leaving desposits )


  20. Etna erupted on the 21st, making a flow to the southwest. Was the first paroxysm since early 2022, hopefully not the last of 2023 🙂

    It is really something interesting with these eruptions. Etna used to do quite frequebt large flank eruptions, often at low elevation. Paroxysms happened but rarely, and were typically major events with significant summit restructuring. The last flank eruption proper was in 2001 and 2002, separate eruptions but using the same dike, and the combined volume is some 0.4 km3 of material, one of the largest in centuries. But Etna has been only ever more active since then, with hundreds if paroxysms, some being among its most powerful in history, which considering Etna has the longest recorded history of any volcano, this really speaks volumes… More than one of the 2021 fountains was over 1.5 km tall, one maybe even 3 km, but at that point it might not count as a lava fountain I guess.

    I thought this was a precursor to flank activity but it seems it is not at all, because all the paroxysm phases recently have seen net deflation. Seems Etna is not like Hawaii, and actually can do the vertical plinian eruptions on their own, not as a side effect of a flank eruption, although 1669 was similar to a Hawaiian eruption. So maybe the next millennium at Etna isnt for it to collapse like Kilauea, flooding the surrounding landscape with lava, but rather to grow into a towering giant, the SEC is going on a couple hundred meters, and is mostly under 15 years old, and all 4 summit vents have been highly active in the past decade, only Bocca Nuova hasnt had at least one true paroxysm.

    • Etna have weak flanks too so prone to flank eruptions. SEC may collapse into a glowing pyroclastic flow If it grows even taller and steeper, thats what INGV thinks being a pile of scoria and lava flow layers. Etnas magmas are phenomenaly gas rich in water vapour and drives tall fountains

    • If we compare Etna to Hawaii, then it’s Mauna Kea. But what Etna does more steadily, does Mauna Kea in swarm eruptions after millenia of dormancy (maybe 2000 more years to wait?).

      Etna often does mixed explosive-effusive eruptions with ash covering the region and lava flows/fountains at the same time.

  21. A new paper is due to be released today in Scientific Reports that confirms a long-held theory that plasma bubbles in the ionosphere can be triggered by volcanic activity. This upper-most layer of Earth’s sensible atmosphere is crucial for satellite and radio communications…and when perturbations such as plasma bubbles occur, radio-based technologies can be adversely affected.
    The eruption at Hunga Tonga enabled an ideal testbed for the theory, and indeed a disturbance in the ionosphere was detected long before the arrival of the main pressure wave(s)…which in turn points to an electrically-based plama bubble was generated that travelled much faster than the pressure wave moving at nearly the speed of sound.

  22. HVO’s servers are getting hammered something fierce today. They weren’t this laggy on the first day of ML.

  23. Really nice work Jesper, just finished reading and wanted to let you know how much I enjoyed learning about the Pillan Patera eruption! The artwork was a tremendous visual aid and a very nice inclusion in the article, kudos to the artist.

    • These lava falls must have been a sight beyond any mental capacity of imagination! 🙂 even better with the Giant Jupiter in the sky looking on his enraged child ball


    If this pops up on deskop as well
    I think I have discovered an active lava lake in one of Galileos Photos of Chaac Patera Io.
    The lowest frame have a dark spot in a pit and If you zoom in, you can see a shiney black surface crust and even white hot areas of spattering. This looks exactly like the Erta Ale lava lake did in 2000 s. Looks like Chaac Patera have lava lakes in some of its caldera walls. Another clue that dark stationary unchanged spots on Io are probaly basalt lava lakes

    • Interesting, it could be a lake, does have the look to it.
      But it also looks a bit like a wall in shadow too, I think maybe a lava surface would glow more. But hard to say really, in the sunlight it would not be bright.

      • I don’t think the of the wall could project a shadow with that shape, though. And lava lakes only glow if there is spattering, if a lake crusts over it just looks black. Kilauea’s lava lake doesn’t even glow in thermal images at all because it has a very thick crust, so some thickly crusted Ionian lava lakes could even be yellow colored from sulphur frost.

      • They will glow If the are spattering sloshing, or from its fissure crust tectonics, the lava lake here seems to have glowing fissures in its crust in this small lava lake

        Most much larger Ionian lava lakes overturn only by passive overturning rather than convection. Its possible that Loki Patera is just a hole into Io s magma ocean

      • The bright spot on it is sunlight that falls on shiney crust, fluid lava lakes are very shiney as we saw with the Halema’uma’u in 2017

    • Albert some intresting stuff that the staff at JPL simply have No time to look at … I think I will put togther an article on this But the resolution is so low .. But yes it does look like a lava lake!

      A low viscosity lava lake surface will be shiney and smooth and may not glow very much unless there is spattering or plates in the crust that forms glowing rifts. The white areas looks like that

      I WANTS this black and grey to be colored in line with all Galileos filters so you gets a true eye color and Maybe the white will become
      Red in real color ?

    • Im completely addicted to Io…
      And spends alot of free time looking at these Galileo Imagery

      But its soon time to force Nasa to build a ultra high res Io orbiter as my hunger for volcanism have No limits.
      Hopes They does it one day.. althrough its expensive as hell .. the devil of costs and goals is always laugthning in the background and the projects rarely goes off from proposed missions

      But yes I wants more Ionian probes Absoutley: better to be born in year 2300 right ?

    • Its also possible to see tumulus mounds and inflation mounds in Chaac Patera so space pahoehoe and an old channelized vent

    • I agree, it looks like a lava lake. By extension, the other black areas along the left side of the patera must be lakes too.

    • The apparence of this lava lake near Chaac s walls is very strongly suggestive of fluid basalt, but a komatitic lava lake may look similar But one may expect Komatites to glow even more because they are so hot. A komatitic lava river will look like liquid iron slag, white hot active surface and a orange glowing crust If its thin, while a fluid basaltic flow channel have a dark shiney flexible crust below incandensce.

      Ionian lavas are No doubt very fluid, perhaps even more so than Kilauea, But the morphology thats been seen at Prometheous and Here suggest basalt rather than ultramafic lavas

    • I will do an experiment!
      I will lab with Photos of Earths lava lakes mainly Erta Ale and large Puu Oo lakes. I will remove all color and I will lower the resolution and pixelate them. If it looks the same then we have an answer and yes this is a lava lake in that Ionian pit. I agree with Hector it cannot be anything else than a lava lake, having a dark shiney crust and hot white fissures

  25. I suppose that a volcanism similar to that of Io also exists in the deep oceans of Europa.
    This would justify not only the very existence of a constantly warming deep ocean but also the complex web of fractures that cover its surface.
    This means that it is not a calm ocean but a very extremely tumultuous one with extremely powerful ocean currents.
    My compliments for the article.
    Extremely long, detailed, and well written.
    I hope to read more in the future.

    • Yes they belive that seafloor volcanism happens in Europa and that woud make it very habitable for life as volcanoes give energy and nutrients. With lower gravity than Earth, Europas seafloor pressure is not higher than Mariana trench as well

    • Fun you enjoyed it .. indeed Ionian eruptions are another class compared to typical terestrial eruptions. I guess Pillan is only a medium sized Ionian lava flood

  26. It is great, Jesper, also the art by Vitkus. Pretty hard to imagine on such a smal celestial body.

    • Glad you like it : ) well Io is one of the largest moons in the solar system, its just that Earth is much bigger still I guess

      Io is overall small compared to Earth But haves over – sized volcanoes 🙂

    • Thank you .. I wonder what woud happen If Iceland does this .. severe Gas pollution I guess

      Hawaii and Iceland and Africa maybe able to, but luckly Pillan is not the standard eruption on Earth like it is on Io !

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