Hi JimSea.
I read the article familyop linked. The graphic shows a core of basaltic magma--the kind that you find in Hawaii and, as I understand it, flows rather than explodes as Mt. St. Helens. But that basaltic magma has what they call a granitic cap-- and I wonder if that's cause for concern.
Of course there are different kinds of granite--mafic and felsic (sp?), but I don't know if we have a scenario like Mt St Helens, where the lighter and stiffer granitic cap blew and spewed so much ash into the air. Could that happen at Yellowstone?
Thanks.
No, a caldera this large would never erupt explosively. However, even if it’s just “Kilauea”-type eruptions, they would be on a far more massive scale. When this kind of thing erupts, it goes on for thousands of years, and spews all kinds of horrific crap into the atmosphere. A somewhat larger feature like this erupted in India around the extinction of the dinosaurs; the Deccan traps buried a major chunk of the Indian subcontinent under a mile of lava, likely contributing significantly to the damage the asteroid strike caused, and probably would have kicked off a new glaciation period all on its own.
Forgot to add: the Deccan Traps eruptions lasted for ~30,000 years. If the Yellowstone caldera stays active for even 10% of that length of time, it would still be a worldwide disaster.
I can’t answer your question but I know that when the active magma area that is now Yellowstone was under the eastern Washington crust, the lava outflow was all non-explosive.
Yes, I believe you are correct. There is a lot of rhyolitic magma on the surface and that would indicate a rather explosive history and potential for Yellowstone. We know that past eruptions in Yellowstone have been catastrophic certainly. My point was only that different possibilities exist for future eruptions.