“Under the western US is a huge underground partially-molten reservoir of liquid carbonate,” Hier-Majumder added. “It is a result of one of the tectonic plates of the Pacific Ocean forced underneath the western USA, undergoing partial melting thanks to gasses like CO2 and H2O contained in the minerals dissolved in it.”
Normally, when one tectonic plate gets forced under another in a process known as subduction, you get a very complex, layered style of melting within the space above the descending plate as it dehydrates. This ultimately produces large volumes of thick, gassy magma that produces some of the most explosive volcanoes.
Mount St. Helens – and the entire Cascade Arc it belongs to – are prime examples of this type of subduction-zone volcanism. However, every now and then, you get a very weird form of melt appearing in the mix – in this case, plenty of carbon-rich rocks were added to the upper mantle.
When carbon-rich magma makes it to the eruption phase, it tends to produce incredibly fluid, very “cold,” black-and-white carbonatite lava. Several volcanoes in the East African Rift exhibit this type of eruptive activity, which creates some truly alien-looking landscapes.
There isn’t any evidence at the surface yet that carbonatite volcanoes will spring up across the Western US anytime soon, and it’s more likely that you’ll just get very gassy, “conventional” explosive eruptions instead.
Still, give it a few tens of millennia, and hey, you never know, the planet may surprise you – or your descendants, anyway – with its strange volcanic ways.
Will this carbon influence the sort of eruptions seen in North America in the future? saraporn/Shutterstock