We continue where we left in the previous article. Last time we were looking at the eruptions of Mauna Loa in 1852, 1855-56, and 1859. These three large, closely spaced eruptions took place in the Northeast Rift Zone (NERZ) and north flank of the volcano. The next major flank eruption would happen in 1868.
The 1868 eruption
After the eruption of 1859 came a more prolonged dormancy of 5.1 years. An eruption occurred in 1865-66 at the summit, which raged on for 4 months. Following the 1965-66 eruption came a dormancy of 1.9 years until the eruption of 1868, which was in the SWRZ. This follows the “pattern” of Mauna Loa. This “pattern” is that summit eruptions will happen in between rift eruptions, and that rift eruptions will alternate between NERZ and SWRZ. The dormancy between summit and rift is shorter, and the dormancy between rift and summit is longer. This pattern would be cyclic. However, it is a behaviour that has been broken more often than not. Sometimes summit eruptions in a row have happened. Twice there has been a summit-NERZ-summit-NERZ series. There have also been two series of three unbroken rift eruptions, 1852, 1855 and 1859 in the NERZ, and 1916, 1919 and 1926 in the SWRZ. The plumbing of Mauna Loa is in constant change, which is probably the reason no stable, predictable pattern gets established.
The 1868 eruption started on March 27 at 6 a.m. It commenced from the summit as usual. One report mentions the location of this initial outbreak to be near Pohaku Hanalei, a lava cone in the uppermost SWRZ. The initial effusion was over in a matter of hours. Frederick S. Lyman witnessed this eruption from Kau:
“You may have already heard that an eruption broke out on Mauna Loa, a little to the south west of the summit, about 6 o’clock last Friday morning, 27th inst. It gave no forewarning; the fire burst up out of the ground, throwing a spray of red lava high in the air, then a great column of smoke rose straight up thousands of feet and arched over to the east. In a few minutes a new jet was thrown up a little S. E. of the first, with its column of smoke ; soon followed by another jet; and then by a fourth ; soon the red lava began running down the sides of the mountain in four streams in a southerly and easterly direction. About seven o clock we began to hear a roaring sound, which grew louder and louder until the air seemed to tremble with the incessant roar of the volcano; but it finally subsided, and ceased entirely about eight o’clock.”
That very same day, in the evening, a large series of earthquakes started rocking the Kau district, which makes up the south and east slopes of the massive mountain. The next day, March 28, two enormous earthquakes occurred in quick succession, estimated at M 6.1 and M 7.0 in the Catalogue of Hawaiian Earthquakes. A letter from Kau in the Pacific Commercial Advertiser details the earthquakes:
“The earthquakes commenced on Friday night (Mar. 27); some say we had thirty or more shocks. Saturday morning I awoke about daylight, and up to 1 P. M. I counted ninety-seven earthquakes; none were very severe, but their frequency frightened us. While at dinner we had a heavy shock crockery jingled and the house creaked like a ship in a storm. I left the table and went over to _ and while talking with them we had a fearful shock. I caught up one child, and another, and little _ and _ followed, running out of the house, while vases, books, boxes, lamps and dishes were falling about us. When we got out, walls were falling down with a thundering noise, and the air was filled with dust, the earth still quivering. In less than twenty-four hours we had over two hundred shocks!”
According to Abraham Fornander, who was at the Volcano House that day:
“The first (heavy) shock was felt throughout, Kau, Puna and Hilo. At Keauhou, the ground shook continually all the afternoon on Saturday. In Kau, the shock seemed to have been stronger the more southward you went. At Waiohinu, it shook down walls, and cracked the stone church from top to bottom. At Kahuku, Capt. Brown’s place, the dwelling house, cattle pens, stone walls, etc., were thrown flat on the ground fortunately no one was hurt”
Mrs. Sarah Joiner Lyman, who lived in Hilo, kept a diary of felt earthquakes. This diary, which was later continued by her son and his wife, records a list of earthquakes felt in Hilo for eight decades. She writes:
“Saturday (3/28) is a day ever to be remembered here: in less than half a day, there were 51 decisive shocks, one of which was the strongest shock that the oldest inhabitant has experienced . . . This occurred at 1:28 pm. This lasted for some time, causing everything to rock backward and forward”
What exactly was going on? The smaller frequent earthquakes being felt on the night of March 27, and the morning of March 28, would have probably been caused by a magma intrusion propagating into the Southwest Rift Zone. The intrusion had broken out near the summit of Mauna but was now making its way underground. Frederick S. Lyman mentions a line of smoke propagating down the rift zone. This line of smoke may have already reached a location just above Kahuku by March 29. But because he may have had later knowledge of the lava breaking out near Kahuku I’m not sure how reliable this is.
The flank of Mauna Loa is slowly sliding away into the sea. The way it does so is more complicated than a simple slump. I will explain more about this later. The intrusion had triggered the faults under the mobile flank into the major M 7.0 rupture of March 28. Earthquakes continued, now aftershocks from the M7.0 were likely being mixed up with quakes from the continuing intrusion.
“On the 30th and 31st, and April 1st, a number of shocks were felt at Hilo, some of them sufficiently powerful to awaken persons from sleep, causing furniture, etc. to rattle”
In Kau people were being awakened multiple times each night by vigorous shakes. Some considered that lava was trying to break out, and until it erupted, there would not be much rest. Unfortunately, the worst earthquake was still to come:
“The heaviest shock occurred Thursday, April 2nd, being the same that was felt so sensibly at Honolulu. This destroyed every church and nearly every dwelling in the whole (Kau) district. From 10 to 12 o’clock of that day there had been
service in the large church in Waiohinu, and it was crowded with people. Only four hours after they left, the heavy shock came, the walls tumbled in, and the roof fell flat all the work of twenty seconds. At the same instant, every man, woman and child was thrown off from their feet. Horses and cattle dropped down, as if dead. A man riding on horse back had his horse tumble under him so suddenly that he found himself and horse lying flat on the ground before the thought of an earthquake entered his mind.”
The earthquake of April 2nd would be known as the Great Kau Earthquake, is estimated as M 7.9, and is the largest earthquake in the history of Hawaii. Professor Frederick S. Lyman found himself near the epicenter of the earthquake in Keaiwa, close to the present day location of Pahala:
“First the earth swayed to and from north and south, then east and west, round and round, then up and down and in every imaginable direction, for several minutes; everything crushing around us; the trees thrashing about as if torn by a mighty rushing wind. It was impossible to stand, we had to sit on the ground, bracing with hands and feet to keep from rolling over. In the midst of it we saw burst out from the pali about a mile and a half to the north of us, what we supposed to be an immense river of molten lava, which afterwards proved to be red earth, which rushed down its headlong course and across the plain below, apparently bursting up from the ground, throwing rocks high in the air, and swallowing up everything in its way, trees, houses, cattle, horses, goats and men, all in an instant, as it were. It went three miles in not more than three minutes time, and then ceased. Someone pointed to the shore, and we ran to where we could see it. After the hard shaking had ceased, and all along the sea-shore, from directly below us to Punaluu, about three or four miles, the sea was boiling and foaming furiously, all red, for about an eighth of a mile from the shore, and the shore was covered by the sea.”
The rupture of the earthquake propagated across the entire south flanks of Mauna Loa and Kilauea and relieved compressive stress than had been built along the shore of the island from the upper flank, creeping downward and pushing against the locked portion of the flank. The coast subsided 1-2 meters for a distance of 110 km, from the east point of the island, Kapoho, to the south point, Ka Lae. Near Kapoho coconut groves now stood underwater at high tide. The subsidence as far as Kapoho can only be explained by the flank of Kilauea shifting away together with that of Mauna Loa. Likely this same fault later ruptured in 1975 and 2018.
At the same time as the subsidence, the sea rose up, pushed away by the motion of the submarine slopes. A tsunami claimed 46 lives. Villages were entirely destroyed by the tsunami and coastal subsidence. Some villages weren’t resettled, which was a good choice, for a 1975 earthquake again produced a tsunami in those same areas. Old volcanic ash from Kilauea, the Pahala Ash, was triggered into many mudslides from Kapapala to Waiohinu. One of these mudslides, described by Lyman above, caused 31 fatalities.
At the time of the earthquake, Kilauea had a lava lake that covered much of the caldera floor. It had filled and drained multiple times. After the previous draining in 1840, it became concealed by a large thickness of lava flows and had pushed up the centre of the caldera like a piston about 100 meters by 1846. This activity had continued up until 1868, with decreased strength. The M 7.9 April 2nd earthquake created a sudden extension across the rifts and summit of Kilauea, and it was seemingly strong enough to start a sudden dike intrusion. An hour after the earthquake, lava erupted in the Kilauea Iki crater. A dike formed from the lava lake and followed the typical trajectory of Kilauea summit dikes. East into Kilauea Iki, and also west into the Southwest Rift Zone of Kilauea. In a few days the whole central region of the caldera had fallen by almost as much as it had risen since 1840, leaving an empty bowl as the lava lake drained away, which would be the final destruction of the caldera-wide lava lake that had grown since 1790. Some small amount of lava erupted later, on April 9, in the Southwest Rift Zone. The physician William Hillebrand described Kilauea after the earthquake:
“The great south lake Halemaumau is transformed into a vast pit, more than five hundred feet deep, the solid eastern wall projecting far over the hollow below . . . More than two-thirds of the old floor of Kilauea has caved in and sunk from one hundred to three hundred feet below the level of the remaining floor.”
This rather unique series of events was still far from over. On April 6, at 4 PM, earthquakes in the Southwest Rift Zone of Mauna Loa suddenly reinvigorated, as recorded in the earthquake catalogue, a series of numerous felt earthquakes had started, with 8 events within just an hour. I think at this time the summit of Mauna Loa may have started collapsing. That very night, an explosive eruption scattered ash across the Kau district:
“During Monday night [April 6-7], prior to the eruption, the ground throughout the district was covered with a coating of fine sand and light pumice stone, of a light yellowish color. Where this shower of sand and pumice stone came is as yet unknown”
“April 7th.–The deck [of a ship anchored at Kaalualu] covered this morning with very fine ashes”
The only eyewitness report of the eruption seems to have been from Abraham Fornander, who saw the eruption from Hilo:
“April 7. Last night, between 12 o’clock and daylight, several right smart shocks were felt here. I was awaked four times by the shocks and the rattling of things in and about the house. At 6 o’clock, A. M., as I and others were standing near the Wailuku bridge, looking up at Mauna Loa, a heavy, dense, dark column of smoke, deeply tinged with red at its base, rose from near the top of the mountain, apparently from the southern side of Mokuaweoweo. Though afterwards the smoke grew thinner, yet it remained visible for nearly an hour, with every now and then that lurid glow of red at its base.”
I will explain below why I think the summit of Mauna Loa may have collapsed during this explosive eruption. Magma was on the move again on April 7. That very morning a crater opened up some miles above Kahuku, and seemingly it did so near some farms. When I was reading this report, I recalled a comment from Chad in part 1 of this article. He had found a pit crater that lined up with the 1868 fissures, that more or less could fit with the reported location of the new crater of April 7 that I was reading about. There is a description of the crater:
“The new crater, when visited by Mr. Swain, was at least one and a half miles in extent, nearly circular, but constantly enlarging its area, by engulfing the sides. While the above gentleman was looking at it, a tract of at least five acres In extent tumbled in and was swallowed up like food for the devouring element. The enlargement is going on mainly the lower side, towards the farm houses.”
The crater of chad is smaller than the one described here, but it is circular and located more or less where it should be according to the few descriptions. Horizontal distances are often exaggerated in these old historic reports. The crater in reality is only 150-180 meters wide. Reports shows it grew like a sinkhole. Ground collapsed into it. These pits are sometimes found along dikes. They are very common in Mars too, called catenae. It was likely formed due to the rock above the dike collapsing into the magma and being carried downstream..
The formation of this crater shows magma was rapidly moving down rift. Somewhere at 6 PM lava broke out 4 km downslope from the earlier crater. It did so at elevations of 920-670 meters. No eruption had taken place this low in the Southwest Rift Zone for more than 2000 years:
“On Tuesday afternoon, at 5 o’clock, a new crater, several miles lower down, and about two miles directly back of Captain Brown’s residence, burst out with a heavy roar and frightful crash. The lava stream commenced flowing rapidly down the beautiful plateau, towards and around the farmhouse, and the inmates had barely time to escape with what clothes they had on, before the houses were all surrounded and enclosed with streams of fiery aa lava, varying from five to fifty feet in depth. Fortunately all the inmates escaped safely to Waiohinu, but how narrow the escape was, and how rapid the stream flowed, may be inferred from the fact that the path by which they escaped was covered with lava within ten minutes after they passed over it.”
“At six p.m., when the point was about ten miles astern, bearing E. by S., a volume of flame shot up from the mountain Loa, in what appeared to be the neighbourhood of Kahuku. The heavens were lighted up at once, and the reflection extended rapidly in the direction of Waiohinu and Kaalualu. . . It reached the sea somewhere in that direction at nine and a half p.m., when an immense body of steam at once arose, through which flashes resembling lightning were constantly darting as long as we were in sight. The top of the mountain was concealed by the dense clouds of smoke (maybe dust or ash from ongoing collapse?).”
The lava advanced rapidly near the fissures as thin flows of aa lava, Lava made small streams, creating numerous islands that were not flooded, called kipuka. One family was apparently trapped inside their house in a kipuka for ten days. Several cattle were reportedly stranded in these islands for days until they were rescued.
Where lava rushed into the sea, it exploded and ejected pyroclastic material that built cinder cones around the two principal entries. The largest with a crater diameter of 400 meters. A perpetual thunderstorm played above the eruption, fed by steam from the ocean entry. This plume could be clearly seen all the way from the neighbouring island of Maui, as shown in the following excerpt:
“During the night of April 7th a bright but varying crimson light over the volcano was visible from the Seminary at the distance of one hundred and twenty statute miles as measured on Wilkes’ chart. This light was a reflection from a mass of cumulus cloud through which vivid lightning was constantly darting. After daylight and through the morning of the 8th, this stupendous column of cloud was visible pouring rapidly up to the ether, with ever varying shape. It was usually well defined on the westward side, where it, at times, presented a perpendicular wall of miles in height. On the east it was ill-defined. Above, it often spread out, especially toward the east, as if borne off by the southeast wind of the upper air. The base, so far as visible, appeared to be commingled with murky brown strata. The apparent altitude of this cumulus above the horizon, when at its highest was 3°30′ which reduced for a base of 120 miles with 500 feet altitude of the point of observation, gives a height of 7.8 miles.”
Mr. H. M. Whitney visited the eruption on the 10th of April and gives a great description:
“On ascending the ridge, we found the eruption in full blast. Four enormous fountains, on a line a mile long, north and south, were continually spouting up from the opening. These jets were blood-red, and yet as fluid as water, ever varying in size, bulk and height. Sometimes two would join together, and again the whole four would be united, making one continuous fountain a mile in length. From the lower end of the crater, a stream of very liquid, boiling lava flowed out and down the plateau, a distance of two or three miles, then following the road ran down the precipice at an angle of about 30º, then along the foot of the pali or precipice, five miles to the sea, the stream being about eight or ten miles in length, and in some places half a mile wide. One peculiarity of the spouting was that the lava was ejected with a rotary motion, and as it ascended both lava and stones rotated always in one direction towards the south. . . It lasted only five days, the eruption ceasing entirely on the night of the 11th, or morning of the 12th. During its continuance, the atmosphere was filled with smoke so dense that the sun appeared like a ball of fire, and the whole island was shrouded in darkness. . . As the lava entered the sea, clouds of steam and smoke rose up, and flames of bluish fire were emitted, rising from the water to a height of from ten to twenty feet. During the night we were at the volcano, the air was highly charged with sulphurous gas and electricity, and frequent flashes of lightning were seen directly over the lava stream, accompanied with short claps of thunder.”
The volume of the 1868 eruption has never been properly estimated, given that most lava was dumped into the sea. With the help of bathymetric data, I measured the submarine lava deltas of the 1868 eruption the best I could. There are two lava deltas, the largest, the northwest delta, has about 0.14 km3, while the southeast delta has 0.08 km3. The subaerial volume is about 0.065 km3. Taken altogether, the eruption totals roughly 0.25 km3 or about 250 million cubic meters of lava, which does put it as one of the largest eruptions of Mauna Loa, although still behind 1859, and probably behind 1950 and 1880-81 too.
The flank eruption of 1868 was, however, of remarkable intensity, lasting only a little over 4 days, the averaged eruption rate was 700 cubic meters of lava per second, and the ocean entry may have been the most intense Hawaii has seen in historical times.
Did the 1868 eruption and intrusion make a caldera?
There are several lines of evidence that 1868 was a caldera collapse of Mauna Loa. The caldera of Mauna Loa, as we see it today, formed probably in 1710, in the Hapaimamu eruption. In this caldera, there were several pits, presumably from different collapsed magma chambers. The Inner Pit was the deepest, placed in the centre of the caldera. A nested crater. It is to Mauna Loa what Halema’uma’u is to Kilauea. The Inner Pit is known to have collapsed again at some point between 1841 and 1874. A detailed survey of the caldera in 1874 found the Inner Pit to be 80 meters deeper than the previous survey in 1841, even though the pit had been rapidly filling with lava since 1871, and that summit eruptions in 1849, 1851, and 1865, had also added lava to the crater. No one has attempted to link this collapse to any particular eruption.
Of the eruptions that took place between 1841 and 1874, only 2 of them had very high eruption rates and occurred from low elevations, 1868 and 1852. Other flank eruptions in 1843, 1855, and 1859 were slow and long-lived. The 1852 eruption doesn’t seem to have been particularly big, nor is its intrusion too exceptional. Instead, 1868, had a massive intrusion, as I will explain, possibly the largest historically. The eruption itself was remarkably intense. Its lava carries as much as 30% olivine, a higher content than other historical eruptions, likely showing how deeply it drained the storage of the volcano. 1868 erupted from lower elevations than major prehistoric caldera-forming events, like Hapaimamu or Panaewa. This alone makes 1868 the preferred candidate for collapsing the summit.
Caldera collapses are often linked to explosive eruptions. This was seen at Kilauea when it collapsed in 1924 and in 2018. The shield Piton de la Fournaise in Reunion has also usually exploded when its summit collapsed, as well as Karthala, Fernandina and possibly others. Mauna Loa has also sourced explosive eruptions. Explosive eruptions of unknown timing have scattered blocks of lava and gabbro, as large as 2 meters across, around the Inner Pit of Mokuaweoweo. The April 6-7 explosion of Mauna Loa described from Hilo came from the summit. This explosion, given that there is no other known mechanism that could have triggered it, would have likely been caused by a collapse of the summit of Mauna Loa, and may or may not have contributed to the ejected blocks around the Inner Pit.
Lastly, lava erupted in the caldera in 1871 and ponded into a lava lake that gradually rose up within the Inner Pit until 1877. When you open a hole the volcano will try to fill it up. We’ve seen this with Kilauea after its 2018 collapse, with a huge lava lake that seems to be intent on filling up the caldera. Other past collapses of Kilauea have filled rapidly too. No historical summit eruption of Mauna Loa has lasted beyond 5 months, except for 1871-1877. This very unusual activity must have been the response of the volcano to the Inner Pit collapsing into a crater.
Why so many earthquakes?
The 1868 intrusion stands out for the dramatic earthquake swarm it triggered. Tens of earthquakes were being felt in Kau within a day of the initial summit outbreak, and before any of the major flank ruptures happened. Reports claim more than 3000 earthquakes were felt in 12 days. Highly exceptional. As I mentioned in the previous part about the intrusions of 1852, 1855, and 1859, none of them had any felt earthquake. At the time of the 1984 eruption in the Northeast Rift Zone, there was already a dense seismic network in place. As recorded by the USGS catalogue, the 1984 intrusion produced just five M 3 earthquakes up at the summit, no located earthquakes along the rift, and just a few M 2 earthquakes down the flank, that are too small to be felt.
Another oddity of the 1868 intrusion is that the crater and fissure of April 7 are offset from the “main” rift, about 7 kilometres off to the east. The main rift here refers to the line followed by dikes that intrude directly from the summit, following the direction dictated by stresses, like in 1950. The direction of the dikes seems roughly common to all fissures and fractures of the rift zone, including those of 1868. The problem is, a dike following the direction of the rift cannot possibly end in the location the 1868 intrusion did. A more complex intrusion geometry is needed. While there might be more than one possible option, there is only one I can see that solves both problems at the same time.
It is important to understand the structure of Mauna Loa. The flanks of the volcano are sliding away from the summit and rifts. The southeast flank of the volcano seems to be ever so slowly sliding away.
Mauna Loa’s SWRZ is surrounded by a ring of faults, normal, reverse and strike-slip, and their main function seems to be accommodating outward slip of the volcano. The majority of the faults seem to deep inwards towards Mauna Loa, and are, as such, reverse faults. Many large Hawaiian earthquakes, like 1975 or 2018, have thrust focal mechanisms. So yes, the flank is sliding up slope. Is this even possible? I think we are not dealing with normal slumps, but that instead magma aids in this motion. Below is a map of the faults. I mapped these faults with the catalogue of Robin Matoza, which relocates the earthquakes, and dramatically sharpens their coordinates.
There are many superimposed faults. Kilauea’s south flank has two or three major overlapping thrusts. There are at least 5 major faults running under Pahala, and this is not even considering the mayhem happening deeper down. These faults are probably inter-connected, the areas in between them probably move only during major ruptures. The faults shown are only those being affected by slow continuous slip, which generates strain and many small frequent earthquakes. The south flank of Kilauea for example has had ~40 very small quakes this week. At Kilauea the slip of the upper flank pushes against the lower flank and raises it up. We can see this in GPS data or InSAR. Apua Point, at the coast of the island, next to Kilauea’s most actively seismic part of the flank, has been uplifted by about 10 cm since the 30 cm subsidence during the 2018 earthquake.
But what is most remarkable about Mauna Loa is the enormous area of aseismic slip east of the SWRZ. And I think this is very important. For a distance of 12-16 km from the rift, the southeast flank slips in an almost completely aseismic manner, that then encounters an arc of strong, continuous seismic activity which encloses the area. A further clue as to what this area is comes from gravity. Studies have discovered that the area south and east of the rift has a high gravity anomaly, meaning there is dense heavy material under the flank. Presumably gabbro and dunite, which are dense crystalline cumulates deposited within intrusions.
This is what I believe happened. The structure is like a magma lubricated slide. The upper flank slips over the magma and/or crystal slurries and exerts pressure against the lower flank, causing frequent earthquakes where the two portions clash. I think in 1868 an inclined sheet intrusion started at the summit and then propagated downward through the slump detachment surface. It may have reached several kilometres downward, approaching the seismic arc. The upper flank would have started sliding faster over the intrusion, creating strain across the seismic arc, and numerous earthquakes. Eventually, the force would have been large enough to shift the entire flank away, probably all the way to the submarine edges of the volcanic pile. This was the M 7.9 earthquake. When the leading edge of the intrusion reached the end of the slump, it switched to growing a a vertical dike, erupting offset to the east from other fissures. The following is the speculative geometry of the intrusion:
Intrusions in 1887 and 1907 would have also intruded the slump structure and erupted offset to the east. 1887 also generated a massive earthquake swarm, with hundreds of felt earthquakes in a matter of days, although none as large as the March 28 and April 2 earthquakes of 1868. 1887 and 1907 intrusions were increasingly shallow. From 1916 onwards, intrusions in the SRWZ would have been mostly shallow vertical dikes. An intrusion like 1868 is probably a rare event, and in fact last time lava erupted so far down and offset from the rift was more than 2000 years ago.
I think that slip over outward dipping sheets of magmas and crystal slurries is the force driving the reverse faults around Mauna Loa. It would be an improvement over the deep rift model, where these forces seem to be somewhat unclear. I took inspiration from an article on Piton de La Fournaise by Quentin Dumont and his team. This article shows how sill intrusions of the past 20 years at Piton de La Fournaise have intruded downwards into a detachment of the flank and created slip. I found this article very insightful. Piton des Neiges, the ancient volcano of Reunion that came before Piton de la Fournaise, has known exposures of sills intruded into a detachment/slump of the edifice, on top of a large gabbro intrusion that is perhaps akin to the high density material under Mauna Loa’s SE flank. Related processes may be at work in Hawaii.
The 1868 eruption and intrusion was a disastrous event for Hawaii. It is probably something that will not repeat again for a long time. There is much to learn from it, and there is much we will never know. In these past 2 articles, I have looked at Mauna Loa and shown what a fascinating volcano is. And also terrifying when it wants to. While people wait for the next eruption of Mauna Loa I look at the past and see many eruptions, and am amazed at the scale and complexity of the volcanic processes shaping the island of Hawaii.
Links and references:
Various releases of the Hawaiian Gazette and Pacific Commercial Advertiser that cover the 1868 eruption:
Catalogue of Hawaiian earthquakes (Klein and Wright):
Holocene eruptive history of Mauna Loa volcano, Hawaii:
A very personal account of the 1868 events:
Relocated catalogue of Hawaiian Earthquakes (Matoza):
Zurek et al, 2015, article with analysis of bouguer gravity data:
22 years of satellite imagery reveal a major destabilization structure at Piton de la Fournaise: