Update May 8
No major changes. The lava pond in Kilauea is now reported as 220 meters down, and may still be dropping. The most recent images suggest it is still going down. Below 400 meters there would be a risk of ground water getting into the hole with phreatic consequences, but so far there is no indication things will get that far. The tilt i still changing, at a uniform 20 microradians per day (as pointed out in the comments, that is 20 millimeters change over a 1-km length. In practice, the length over which the change happens is not known from a single measurement.) Assuming a circular area of radius 1km, this means a magma outflow of 50,000 cubic meters per day. The tilt in the eastern rift area is beginning to stabilise. A better number come from the GPS which has shown a downward movement of just over 10 cm so far of which half was just in the last day.
Pu’u’o’o is little more than a hill with a big hole. There is no lava left in it; it has all been drained into the eastern rift. Almost nothing has made it to the surface: most is in the dike.
Leilani survives although over 30 houses have been lost. The pattern is repeating where a fissure opens, sulphurous gas comes out followed by sputter, thick lava begins to creep by after a few hours the fissure stops and the lava grinds to a halt. The most recent fissures are on the west side, beginning to extend beyond Leilani itself. PGcam is now a bit far from the action. Cracks in highway 130 suggests that area is at risk now: activity may be shifting west a bit although that is not a promise! The highway is reportedly closed in this location. The sequence and lack of real lava suggests that the fissures are caused by degassing of underground magma. The gas comes up, collects just below the surface and forces a fissure to open. A bit of lava follows but the gas is coming up much faster than the magma. The longer it takes, the more it becomes that the magma will stay down, at least in this location. However, if a larger conduit opens up things could worsen rapidly.
Seismographs remain noisy around Leilani but are rather quiet around Kilauea. Mauna Loa is also keeping its head down.
Update May 6
New fissures are continuing to open, as the previous ones die down. What would normally happen is that one long fissure opens, before after a day or two reducing to a single point of eruption. Here the rift opened but there wasn’t enough pressure underneath so it alternates between different parts. The fountaining has increased to 70 meters, so there is now more oomph, but the eruption has not yet settled down. There is a risk of a fissure opening up in highway 130 (cracks are reported there) whihch would cut off one of two escape routes from the coast.
Update May 5
Over the past day there have been interesting developments. The fissures have continued. There have been 6 reported centres of activity, including one just to the east of Leilani. The fissures behave similarly: a crack develops due to movement at the surface, gas comes out, and sometime later bits of lava are ejected at some speed. The burning fragments go some tens of meters high at most. No effusive lava appears and the ejecta stay within a few meters of the fissure. A video of the third fissure, courtesy of the USGS, is here. The first five fissures have all ceased activity.
The limited amount of lava suggests that the main magma dike below has not been breached. Only a little magma has been forced up underneath Leilani so far.
The earthquake activity has been worldwide news. The inflation has triggered movement on a fault running underneath the south coast, first pushing the upper crust out, followed by some sliding outward on the other side of the fault. The M6/9 is not huge to Hawaii standards but it is the largest earthquake to hit the US this century outside of Alaska. The large change in tilt at Kilauea following the quake suggest a vertical movement of 0.5 meter. (HVO has now reported that GPS measurements gave 0.5 meter of slip along the flanks of Kilauea, so that agrees pretty well with our number.)
The image above shows the location of the fault. Here the earthquake is plotted at its first reported depth. Later analysis moved it up to around 6km depth, putting it on the Hilina fault. It is part of the normal movement along this fault, which tends to occur in earthquakes of M7 or so. The last one was in 1975 and it is plausible this earthquake was due to happen soon already (stress was ready and waiting) and the earlier M5.7 pushed the stress over the limit where static friction could not hold things together. The eruption was thew trigger but not the cause.
What happens next? So far every day has been surprise! The most likely surprise for today is that nothing happens. The eruption now has to wait for more pressure to build up before the magma breaks through more forcefully, and perhaps not quite in the same place as before. But lots of other things could happen. HVO is expected that more fissure vents will open around Leilani because inflation in the area is still continuing. It is also worth keeping an eye on the coast southwest of Kilauea, where the Hilina fault has also moved and a swarm of quakes followed near the surface. This lies near the location where HVO has stated Kilauea’s magma supply may be located, with regular deep earthquakes. The area was utterly silent before the M6.9 but has come to life since.
Keep posted, and keep sending us you info!
May 4: the Puna eruption.
The expected eruption came some time after a M5 earthquake. It started with deformation and cracks appearing in the Leilani estate area.
The east rift zone extends from Pu’u’O’o to the coast and in fact there are some cones just off the coast, safely under water. The earthquake activity occured in clusters along the entire rift. There were also earthquakes off the coast. It was unclear where the magma would reach the surface. The rift stopped extending and little happened for about a day. However, once cracks appeared in the road surfaces, it was clear a weakness had been found.
At first the cracks were only on the surface and there was no evidence for heat or gas emission. However, after a while SO2 began to rise and in the afternoon of May 3, lava erupted from a 150-m long fissure. It was energetic but not voluminous, and the eruption ceased after 2 hours with lave within 10 meters of the fissure. Three further fissure events nearby followed. In all four cases, fountaining reached 30 meters high but the lava did not really begin to flow.
The first fissure was close to a geothermal pant. This might be seen as an energy bounty, or one may wonder whether the drill will provide a magma conduit!
The first three fissures are shown in the map. The fourth one was reported to between the first and third fissure. The four events are aligned with each other. A fifth one may have opened near the geothermal plant. It appears that the pressure was insufficient for the entire rift to open at once, and only parts are becoming active, perhaps slowly merging into a full fissure. The amounts are small and the pressure behind the eruption seems limited. However, the events are within an inhabited area and damage to property seems a certainty. Two houses (or structures) are reported to have been destroyed.
It is not known how the events will develop. This may fizzle out, or it may be the initial stirrings before the main magma flow reaches for the surface. The major deflation at Kilauea has started, but the magma from there will not yet have reached the site of the current eruption. It it does, a more significant eruption could be triggered. It is also possible this will cease, and a new fissure will open west of highway 130. If the current fissure develops, a number of houses at Leilani are at immediate risk. Further downhill towards the sea is a fairly empty area with few dwellings.
There was some discussion on the risk of a flank collapse. That chance is near-zero. The flanks have shown slow-slip events but these are normal part of the settling of Mauna Loa. Nothing at the moment points at an instability, and neither would one expect that an eruption triggers a collapse: a major earthquake s more likely to do this but the flank has survived M7+ earthquakes in historical times so it seems stable. No worries.
An M5.7 quake hit in the same area as the previous M5 events, followed by after shocks. these are between PU’u’O’o and the coast and likely caused by the pressure loss of the magma chamber.
The map shows the location of the earthquakes (as of yesterday) on the deflation map. The M5+quakes are south of Pu’u’O’o, in the area of deformation that runs along the coast. Most of the earthquakes are along the upper line of the deformation.
Pu’u’O’o has lost its entire 20 centimeters of extension in the most recent GPS data, and the eruption there has ended. The chances are that it will restart in the next weeks or months. However, could this herald the end of the 30+years of near-continuous eruption? The larger the Leilani eruption, the bigger the risk to Pu’u’O’o.