Today’s big activities were: (1) massive lava fountains/flows in the Lower East Rift Zone/Lower Puna, entering the ocean at two points (2 modest ash explosions from Halema’uma’u crater (they looked to me like the 10,000 foot range). I’m going to stop worrying about whether they’re triggered by steam explosions or rockfalls.
Late afternoon HNN update includes footage of lava entry into ocean:
The first two weeks of sputtering fissures, slow-moving flows were prelude. Thursday night, the rivers and fountains of runny pahoehoe lava arrived. Today, Saturday afternoon, the overflight videos are historic.
From USGS (loud helicopter):
Fissures 16-20 joined up this Saturday and are marching towards the ocean, expected to cross Highway 137 tonight. Civil defense warns to keep away from ocean entry, if/when the lava reaches the shore, to avoid “laze.”
From Mick Kalber:
I have no words.
Well, okay, I do. I hope everyone down there is safely away. It’s been a hard day for a bunch of people who can’t go home now.
USGS reports another explosion last night: “At 11:58 PM Local time, a short-lived explosion at from Halema’uma’u created an ash cloud that reached up to 10,000 ft asl and was carried southwest by the wind. Possible trace ash fall may have occurred along Highway 11.”
I’m not sure whether this was a steam explosion, or just yet another of these rockfall-triggered ashclouds, like this one in 2011:
Hawaii Volcano Observatory is so lucky to have one of the foremost experts in explosive eruptions, Don Swanon, who worked on St Helens so long ago and uncovered Kilauea’s explosive history after transferring to HVO in the 90s.
Experts on this active volcano gathered to share what they know- and what they have discovered is Kilauea has a history of explosive ash eruptions. Hawaiian Volcano Observatory geologist Don Swanson sums, “For the past 2,500 years we’ve had explosions more than 50% of the time, so this is the norm for Kilauea. But most of the explosions are minor, like we saw today, with small plumes of ash and steam rising from the summit.”
The factsheet notes that “Many of Kilauea’s pre-1924 explosive eruptions that produced significant ash deposits probably happened when the volcano’s summit crater was so deep that its floor was below the water table, letting ground water seep in to form a lake.”
If I’m understanding correctly, they’re saying that bigger explosions may happen when there’s a lake of water, i.e. more fuel to create steam.
“Having pieced together the recent geologic past of Kīlauea, scientists conclude that the volcano will eventually return to a long period of mostly explosive activity, just as it did around 1500 CE. This future explosive period will probably accompany a significant decrease in the magma supply rate and be initiated by collapse of a new caldera to the depth of the water table, which today is about 615 m (2015 ft) below the present high point on the caldera rim. For now, effusive eruptions dominate Kīlauea.”
Note: that’s a new caldera, the much larger basin containing Halema’uma’u crater within it, and the vent that’s erupting ash explosions right now was a small lava lake covering only part of the floor of Halema’uma’u. Orders of magnitude different in terms of size. Also, changing the location of the active vent doesn’t mean the magma supply inside is dropping.
May 15, 11:05 AM: A major ash explosion up to 12,000 feet — which HVO still guesses was caused by rockfall into the receding lava lake— prompted HVO to raise the aviation alert level to RED, warning aircraft to stay away from the summit and ash hazards.
Unfortunately, news media took this RED ALERT to be “major eruption imminent,” instead of “no more imminent than it already is, since, as a matter of fact, it’s already erupting. But it could increase activity.”
Attention shifted back to the summit on May 9, when a 3.1 earthquake set off a rockfall that agitated the lava lake and sent up a 6000-foot poof of ash (video clip National Parks site):
Rockfalls caused poofs of ash like this even back when the lava lake was full, but that was more than usual. (See also USGS video from May 7, when lava lake was still visible, showing how falling rocks agitate it).
However, that was just a teaser. The big news was the dropping lava lake…
…prompted HVO to issue its first warning about steam explosions if the lava dropped below the water table.
Hawaii Volcanoes National Park closed Friday May 11 as a precaution, since the lava lake was projected to reach the water table sometime that day. For the next few days it continued to send up a white plume of steam and/or ash clouds when rocks from the sides of the chimney fell in:
Evacuated residents of Leilani Estates were allowed back on Sunday May 6 to collect vital documents, pets and possessions. New fissures continued to open up and spatter, and officials warned about toxic sulfur dioxide gas (SO2) coming from fissures as well.