September 21, 2014 mud flood on Mount Shasta

Mud at 100 kilometres an hour? It happens. Mount Shasta, in northern California, let loose this afternoon with one heck of a mud flood, apparently caused by a sudden melt of one of its glaciers. Probably not at a hundred kilometres an hour.

The volcanoes of the Pacific Northwest are strikingly beautiful. But it is a haunting beauty. Each time I have looked towards Washington’s gorgeous Mount Baker from Victoria, in Canada, 100 kilometres across the Juan de Fuca Strait, I have had an unnerving sense of the terror that will one day come. On bright clear days, Baker fills the horizon, though often the foot of the mountain is shrouded in mist. On those days, the volcano seems to float eerily above the clouds. The haunting comes, in part, from the knowledge that this mountain will one day violently shake off the lovely glacial ice that coats its shoulders. When this happen, lahars, or volcanic mudflows, will churn hot gas, rocks, and millions of tonnes of slushed glacier into a slurry that will rush down the slope at a daunting velocity. Even at 100 kilometres per hour, a lahar has the consistency of concrete; when it solidifies, the material becomes cement, encrusting the mangled debris it has accumulated on its slide down the mountain

Mount Baker is presently somewhat quiet, having expelled a few belches of gas in 1975, and has had little to say since. The United States Geological Survey is more concerned about nearby Mount Rainier, which has more ice than Baker, is a more active volcano, and sits atop Seattle. Six thousand years ago, Mount Rainier shot lahars down valleys where tens of thousands of homes now stand. Those flows were 150 metres deep and pushed all the way to Puget Sound, 50 kilometres away. Mount Shasta can be expected to perform a similar stunt one day.

Today’s Shasta shake was apparently not due to volcanic activity or any associated earth tremors. Just good old-fashioned glacial melting. This has closed some bridges and muddied some highways, but so far no one is known to have been injured.

Mount Shasta in 2011