The United States is a volcanic country. Sure, a large swath of it east of the Rocky Mountains haven’t had an eruptions of tens to hundreds of millions years, but the western US, Alaska and Hawai’i are all full of active or potentially active volcanoes. This got me wondering what are the biggest eruptions the US has experienced and that led me down a rabbit hole considering what that question actually means.
So, I present you with the largest eruptions in the US over the last 10,000 years. As you will see, this can be a tricky question. To try to normalize thing, I considered “biggest” to mean largest volume of erupted material, the higher eruption magnitude and then the eruption’s volcanic explosivity index (VEI; in the at order). I used the Smithsonian Institution Global Volcanism Program and the Volcano Global Risk Identification and Analysis Project (VOGRIPA) databases for my information.
A few things about measuring volcanic eruptions. First, explosive volcanic eruptions produce tephra, with is a bit of a catch-all for volcanic debris like ash, pumice, bombs, etc. Material like that tends to be full of air pockets, so to put all eruptions on an even playing field as the amount of air can vary, we convert it to a “dense rock equivalent” or DRE. This is a calculation using data about the percent of air in the deposit that then removes the volume of air to get at how much magma was actually erupted. All the volumes here are DRE.
Second, I’m leaning into using eruption magnitude over VEI. Unlike VEI, which uses volume of tephra to rank eruptions, eruption magnitude uses the log of the mass of the erupted material (log10(erupted mass in kg) − 7), thus discounting the amount of air in all the deposits. So, this makes a comparison that is a little more apples to apples and as you’ll see on the list, the VEI and eruption magnitude don’t differ too much.
Onto the list!
