Two Volcanoes: Iceland’s and St. Vincent’s


All of it, gone with the wind now.

What a wild volcano weekend it has been thus far! (Am writing this Saturday evening.)

A seismologist summed it up in this tweet:


https://platform.twitter.com/widgets.js


The processes that he hints at are very cool.

For instance, the eruption in Iceland, as we’ve seen, has roots in the upper mantle. That almost pure basalt lava is very hot and runny. Dissolved water vapor, carbon dioxide, sulfur, and other volatiles and trace metals can easily escape from this stuff, which is why the Icelandic Met Office issues gas contamination forecasts (Icelandic) for visitors to the site as well as for settlements downwind.

In the Caribbean, though, Vincentians are running for their lives from an explosive eruption at La Soufriere.



Nobody is gathering around the flow front and roasting weiners here because it’s too dangerous (also, the lava isn’t as hot and runny as Iceland’s).

And its chemistry is more complex; instead of rising from the upper mantle, this melt is recycled seafloor and sediments, plus contamination from crustal rock.

Why? Because La Soufriere sits in a subduction zone where the Atlantic seafloor is diving beneath the edge of the Caribbean plate.



There are more volatiles — water, sulfur, chlorine, etc. — in the subduction-zone melt, which starts coming out of the downgoing plate about 60 miles underground. It picks up even more of them as it rises through crustal rocks like limestone (carbon dioxide) and granite (water, believe it or not), working its way toward the surface. (Oppenheimer)

At the same time, some of the silica and oxygen atoms present in the evil brew start messing around together, sharing electrons and forming polymer chains that make the magma very thick and sticky.

Gases can’t easily escape this sort of material, even when it erupts and forms a lava dome, as La Soufriere did months ago. But so close to the surface, they do keep bubbling out of the melt, building up pressure.

Fortunately, volcanologists often can spot such things in time to move people out of the way, as they did on April 8-9, just before the inevitable happened at the overheated pressure cooker that was La Soufriere at that time:


Richard Robinson


Now the eruption must run its course, however long and destructive that might be.

Unlike Icelanders, Vincentians are not happy with their volcano, although it, too, is making world headlines.

We laypeople tend to think that all volcanoes are alike. This weekend, we’re learning just how different they can be.




April 11, 2021, 1:06 p.m., Pacific: Just now, they closed a Barbadian streaming press conference on the La Soufriere St. Vincent eruption (Barbados is directly downwind) with the reading of excerpts from a poem that Kamau Brathwaite wrote about ashfall from the 1902 eruption. It provides balance to the above Iceland video in this post about two eruptions that I wanted but couldn’t find until now. All over the world, eruptions bring out our deepest inner thoughts and feelings.




Featured image: Wikimedia, CC BY-SA 4.0.


Sources:

Oppenheimer, C. 2011. Eruptions That Shook the World. Cambridge: Cambridge University Press. Retrieved from https://play.google.com/store/books/details?id=qW1UNwhuhnUC



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