I am a 8th grade student at Albion Public School and I have a question. On CHANNEL ONE NEWS (a news station based in L.A.) they said that the biggest volcanic eruption in North American history was the 1980 Mt. St. Helens eruption. My teacher, myself, and classmates think that they are incorrect. We think that the biggest one is the volcano that erupted in Idaho that caused the animals at Ashfall, NE to die. Please send me some information and the name of the volcano.

rocky Kyle Wyatt

Dear Kyle,

CHANNEL ONE NEWS is wrong. The biggest volcanic eruption in North American during historical time was the 1912 eruption of Mt. Katmai in Alaska. It produced 10-20 times more ash than the 1980 Mt. St. Helens eruption.
But that's not what you are thinking. You are thinking about the biggest one ever. That means in millions and billions of years, not just a few hundred.

The ash layer in Ashfall State Historic Park is 10 million years old. It originated from a volcano in what is now southwest Idaho (west of Twin Falls). The deposit associated with this eruption is called the Idavada Volcanics in Idaho (I don't know if a specific volcano has been identified). This eruption produced a large caldera and is related to a hot spot beneath the North American continent. It would be similar to present-day Yellowstone Park and the eruptions that have happened there. These eruptions are some of the largest on Earth and can produce 1000-2000 times more ash than Mt. St. Helens. Geologist do not have enough information to prove that the eruption that produced the layer in Ashfall State Historic Park is the largest ever in North American. You and your classmates might think about what kind of information geologists need to collect to prove how big the eruption was. I think you can say it was a big eruption, much bigger than anything ever observed since people started writing about volcanoes.

Steve Mattox, University of North Dakota

Sources of Information:
Armstrong, R.L., Leeman, W.P., and Malde, H.E., 1975, K-Ar dating, Quaternary and Neogene rocks of the Snake River Plain, Idaho: American Journal of Science, v. 275, p. 225-251.

Special thanks to the rangers at Agate Fossil Beds National Monument, Nebraska. 

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