What’s taking place right now on Hawaii’s Big Island is as multifaceted an eruption as you’re likely to get. Aside from the eye-catching explosive activity at Kilauea’s summit, you’ve also got nearly two dozen fissures that have opened up in the last few weeks in the East Rift Zone (ERZ). Along with the acidic laze created when their lava oozes fall into the sea, their propagation has destroyed property and triggered sudden evacuations.
As is clearly shown by that spectacular cover shot, courtesy of the United States Geological Survey’s (USGS) Hawaiian Volcano Observatory (HVO), you’ve also got lava fountaining. Although it’s a common feature of plenty of eruptions, including those taking place here, the imagery captured by experts this time around is so resplendent that it warrants an explainer of its own – so what is it, exactly?
In recent days, the volcanism in the ERZ has stepped up a gear; four fissures’ flows have merged into one, which has created an ominous, beautifully singular, anastomosing flow, replete with said fire fountains and heightened, hazardous sulfur dioxide emissions.
The USGS’s latest advisories often speak of spatter – the ejection of blebs of lava from the flows – which is generally triggered by small amounts of rapidly expanding volcanic gases. These gases, once dissolved in the magma, are exsolving under less restrictive atmospheric pressures; they turn into bubbles, which embiggen and fling small amounts of lava all over the place.
Lava fountaining is, crudely put, spattering’s big sister. It comes in a variety of forms, but the same process of rapidly expanding gas applies.
Sicily’s Stromboli – the Lighthouse of the Mediterranean – has a lava fountain-prone eruption style. As the magma here slowly rises through its conduit (its rocky esophagus), the confining pressure on the magma decreases, which allows bubbles to form. These often coalesce into a single, large slug.
When this slug gets to the vent, it “pops”, and this rapid depressurization event flings lava into the air. At night, it illuminates the tiny island, hence the nickname.
This isn’t quite what’s happening at Hawaii’s ERZ; instead, gas-rich magma is continuously degassing at these fissures. It expands as it escapes skyward, sending lava into the air as smaller spatters or more pronounced fire fountains.
Things on the Big Island, however, are even more complex. The geochemistry of the lava has changed in recent weeks. Earlier on, remnants of older, colder, thicker, and less gassy magma escaped to the surface; this allowed for some displays of acrobatic lava, sure, but now that this has been depleted, as first elucidated by Earther, the real fireworks show has begun.
“The recent geochemistry change means we have more fluid lava and more gas, which has led to lava fountaining compared to the lava spattering we saw at the beginning of this fissure eruption,” Dr Janine Krippner, a volcanologist at Concord University, told IFLScience. This gas increase can be seen in the tripling of sulfur dioxide gas emissions in the area in the past few days.
There’s a lot of unpredictability here. As the USGS explains in its latest advisory: “Future outbreaks could occur both uprift (southwest) and downrift (northeast) of the existing fissures, or, existing fissures can be reactivated. Communities downslope of these fissures could be at risk from lava inundation.”
The dangers are real, but it’s hard not to be wowed by the aesthetics of it all. “The fact that we have magma that has come up from kilometers below the surface and is erupting as fountains of gassy liquid rock is incredible,” Krippner adds.