It’s inevitable that I’m going to talk (again) about Kilauea. It’s the geoscience event that’s dominated news media (not always with a great degree of accuracy or responsibility) and disrupted the lives of thousands. The situation is changing so rapidly that the USGS is releasing updates more than its usual once a day, and, just like last week, whatever I write will almost certainly be out of date by the time you read this.
With this in mind I’m going to depart from my usual format, beginning with an update on the current situation and then looking at different eruption types — not news, I know, but useful background. And then, to keep this as a geoscience roundup rather than an earthquake special, I’ll be looking at Antarctica.
Kilauea: What’s Happening?
There are two key components of hazard associated with the ongoing eruption — lava flow and ash/gas, compounded by the possibility of an explosive eruption. By the 15th of May, 2018, there were twenty fissures (vents actually erupting lava) in the volcano’s north east rift zone.
The most recent mention of these fissures in a USGS notification, at issued 12:28 PM HST on 15 May, reported that “the advance of the flow has slowed significantly since yesterday afternoon. At 6:45 a.m. the flow was nearly 2.5 km (1.5 mi) in length”. Such a slowdown need not indicate, however, that the eruption (or this particular phase of it) is coming to an end.
It’s also worth noting that while Kilauea’s activity was largely confined to lava flows, the volcano warning was on orange (indicating limited hazards even though an eruption might be ongoing), it has, in the last 24 hours, been raised to red (indicating hazardous activity).
What hazards are currently an issue for the residents of Hawaii? If we can step back from some of the sensational reporting and sheer speculation, we can look at the science-based realistic assessment from the USGS. These are: the occurrence and increased likelihood of ash fall and an ash cloud (hazardous to health and a risk to aviation); volcanic gas, which is a risk to health; and the possibility of volcanic projectiles (“bombs” near the crater).
And they warn that: “At any time, activity may become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent”.
Volcanic Eruptions 101
I approach this section with a certain degree of trepidation, as I have only a few hundred words to tackle a complicated subject. Once again I have to ask you forgive me if I end up over-simplifying, but I wanted to set out what is possibly the biggest cause of misapprehension among the public — namely, that Kilauea might be about to erupt on the scale of Mt St Helen’s, or even Krakatoa.
Peter Francis’ authoritative volume on Volcanoes divides volcanic eruptions into fourteen types, but the essential difference is between effusive and explosive. In the first, the lava is relatively thin and flows. Hawaiian volcanoes are classics of this mild, though spectacular, eruptive type.
At the other end of the scale are explosive eruptions. Lava is thicker and harder to erupt. Often, a plug of cold lava in the vent of a volcano will allow pressure to build up and eventually reach a point at which the volcano erupts, violently and explosively.
This is where it gets complicated. Volcanoes are products of their tectonic context: we might expect a volcano at a subduction zone to behave explosively and a volcano overlying a hotspot to behave effusively — but there are other factors. And the most important thing to note is that a volcano that typically erupts in one way may also do so in another.
Although the vast majority of Kilauea’s eruptions have been effusive, in this respect, it has form. The key feature in this case, is water. Last week I pointed you towards dramatic time-lapse footage of magma draining from the crater. As this continues, the level of lava drops closer to the water table. With water coming into the system, there is a key ingredient for a steam-driven (phreatomagmatic) eruption.
In 1924, Kilauea erupted explosively and a new item in the Earth scene journal EOS describes how: “scientists counted more than 50 massive explosions over a two-and-a-half-week period. The summit crater of Halema’uma’u doubled in diameter to 1,000 meters in the eruption, and boulders weighing as much as 14 tons were thrown into the air”.
The report does suggest, however, that even in the event of a steam-driven eruption, current activity isn’t on the same scale as that in 1924 and: “any explosions would be localized around the summit, not blow-the-top-off catastrophic blasts like the one at Mount St. Helens in Washington State in 1980, USGS scientists said”.
So there’s a lot to be concerned about in Kilauea — but there’s no need to panic.
Meanwhile, in Antarctica…
And now, as they say, for something completely different. I go on at length about the complexity of the Earth system and how everything matters. So let’s take our eyes off Kilauea and head from Hawaii to the Antarctic, from fire to ice.
This isn’t, yet, a piece about what scientists know but about what they’re trying to find out. We know that global warming is affecting the ice sheets. It has to, under the laws of physics, But we don’t yet know to what extent, or what the implication might be.
Over five years, scientists will be studying the glacier and attempting to determine not just how rapidly the glacier is melting but whether it might collapse and if so, what the implications would be for sea level rise.
As I said – everything matters.