In Alaska, there is a group of six stratovolcanoes on the ironically named Islands of the Four Mountains. These volcanoes are steep-sided and tall, like most stratovolcanoes, and now it seems they may be connected and part of one large underground caldera. As opposed to a mountain, a caldera volcano is a huge pool of magma that can cause the biggest, most destructive eruptions. The most famous is Yellowstone, also here in the United States.

Per the press release: Unlike stratovolcanoes, which tend to tap small- to modestly-sized reservoirs of magma, a caldera is created by tapping a huge reservoir in the Earth’s crust. When the reservoir’s pressure exceeds the strength of the crust, gigantic amounts of lava and ash are released in a catastrophic episode of eruption.

The Islands of the Four Mountains are in the Aleutian island arc that reaches from the coast of Alaska out into the Pacific Ocean. It’s formed like most island arcs on Earth, where one plate subducts, or sinks, under another. In this case, the Pacific Plate is subducting under the North American Plate, giving rise to a long, curved chain of volcanoes.

The press release goes on to explain: Caldera-forming eruptions are the most explosive volcanic eruptions on Earth and they often have had global effects. The ash and gas they put into the atmosphere can affect Earth’s climate and trigger social upheaval. For example, the eruption of nearby Okmok volcano in the year BCE 43 has been recently implicated in the disruption of the Roman Republic. The proposed caldera underlying the Islands of the Four Mountains would be even larger than Okmok.

Now, this theory is by no means certain, and the scientists involved want to go to the Islands and take direct samples of the rocks to match chemical compositions and gather seismic data. This research was done using bathymetry only – depth soundings collected last century. The results will be presented on Monday at the American Geophysical Union’s Fall Meeting.

More Information

AGU press release