The recent volcanic history of Mount Shasta eludes us. For a long time, the last eruption was believed to be in 1786 when French explorer Francois Galaup de LaPerouse claimed he saw it erupting from his ship sailing off Cape Mendocino. This has been soundly debunked. Turns out it was likely a large wildfire started by the local Native American tribe.
On average, Mt. Shasta has erupted every 600-800 years over the past 10,000 years. Today, the youngest eruption we can confirm happened about 3,000 years ago. It seems like we are well overdue for a Shasta eruption, but that’s not exactly how geology works. Volcanoes don’t care about averages as they experience times of high activity and low activity.
The U.S. Geological Survey ranks Shasta fifth among the most dangerous volcanoes in America. Sitting atop the list include Kīlauea in Hawaii, St. Helens and Rainier in Washington, and Redoubt in Alaska. All of those have erupted in the past 125 years, with Kīlauea in 2020 and Redoubt in 2009. While Shasta may not be as active as those volcanos, its long gap between eruptions could bring a big problem for some Northern California locals.
The USGS recognizes that Shasta isn’t a very active volcano (it’s considered dormant but not extinct), with the populated areas surrounding the mountain make it so high-risk. In its report of the most dangerous volcanoes in America, they outline how an eruption could bring devastation to nearby towns:
“Around Mount Shasta an eruption’s pyroclastic flow—rapid currents of superheated gas, ash, and rock caused by a volcanic explosion—as well as ash-infused mudflows could put towns and infrastructure in harm’s way.“
Shasta is relatively young for a volcano. Its plumbing system is still full of magma flowing throughout. In fact, many climbers on its 14,192-foot peak claim to find hot zones in the mountain. During John Muir’s fateful night where he stayed on the mountain during a brutal storm, he claims he was lightly burned by one of the volcanic vents while trying to hunker down from the elements.
It’s unknown what an eruption on Shasta would look like. A highly explosive eruption could be similar to Mt. Saint Helens in 1980, which was the the deadliest and most economically destructive volcanic event in U.S. history. Ash would be pushed into the air in every direction, falling on Oregon, Nevada and the Pacific Ocean. We saw a similar event like that in the eruption of nearby Lassen Peak, which was a somewhat small eruption in the pantheon of volcanoes. There’s also a small chance the mountain could collapse, much like what happened at Crater Lake.
Unfortunately, the time and result of the next Mt. Shasta eruption is unknown, but it’s safe to say it could completely alter the landscape of Northern California.