MT. SHASTA, Cal. -- A series of mud and debris flows have been closing roads and trails around Mt. Shasta in recent weeks. The cause of these debris flows is high up on the mountain, its seven melting glaciers.
These debris flows are known also as lahars. “I think every major drainage at this point on the north and east sides of Mt. Shasta has experienced some kind of flooding, hyper-concentrated flow or a debris flow or a mud flow this year,” says Tyanna Blaschak. She is a hydrologist with the Shasta-Trinity Forest Service and says these flows are due to the melting of Mt. Shasta's glaciers from a lack of insulating snowpack and the heat this summer. "What will often happen is we'll get a debris dam or something like that kind of backed up behind an area where the glacier is melting, and you get some ponding and pooling and what happens at a certain point is that debris dam is going to release that water," says Blaschak. As that water comes down the mountain it has so much mud and sediment in it that it really isn't like water anymore. The flow is able to easily pick up big boulders, logs and other debris making it a threat to people on the mountain. “It is concerning and we just…once things kind of became active this summer, we've just had these continuous like surges coming through on sometimes a daily basis," says Blaschak.
Nick Meyers is the lead climbing ranger on Mt. Shasta and says you can actually hear the debris flows rumbling down the mountain. "We had the chance first hand to see a flow come down, a little pulse to come down on Whitney Creek. We thought it was a jet at first and realized it was the rocks tumbling down the drainage." He says these debris flows have been larger and more frequent this summer than normal, explaining "main impact has been on roads. A number of forest roads have been completely taken out and are impassable by vehicles." Meyers warns, “if you're parked next to one of the drainages or walking along it just being mindful of your location and what could happen if a big flow did come down."
The flows have not crossed over Highway 97 yet near the Whitney Creek drainage but the forest service is concerned with more heat and also thunderstorms in the forecast.
"Further mud flows are certainly possible. If we continue to see what we have been seeing, most of the mudflows have been small to medium in size, but if a big one were to come down, obviously it could do more damage to roads and trails and highways,” says Meyers. Thunderstorms with their heavy rainfall can greatly increase the chances for mud and debris flows. "Anytime we get a rain event, you know situated over the mountain. That definitely exacerbates things and can essentially lubricate everything up there and can cause another mud flow."
These debris flows can be very powerful and can even be picked up by the USGS seismic network on Mt. Shasta. The U.S. Forest Service is working with the USGS to verify these debris flow signals on the seismic network. Scientists and forest officials hope to use the seismic data to better understand these debris flows and hopefully develop an early warning system for people on the mountain. In the meantime, the exact timing of these flows can be hard to predict so the rangers with the Shasta-Trinity Forest Service recommends that if you're spending time on the mountain, be aware of your surroundings. If you hear the rumbling, quickly get to higher ground.
Mt. Shasta is home to seven glaciers and are the largest in the state of California. A study back in 2008 showed that these glaciers were actually growing, overcoming warming average temperatures. This was due to increased snowfall thanks to a warmer Pacific Ocean providing more moisture on the mountain in the form of snow.
But now scientists say this period of growing has ended. "Since then it's actually been shrinking both in terms of migrating further up the mountain and in terms of volume as well,” says hydrologist Tyanna Blaschak. Lead climbing ranger Nick Meyers agrees, “the glaciers are definitely shrinking, and that statement is simply from just a basic photo comparison." Blaschak says we’ve has successive years on Mt. Shasta where we haven’t gotten the snowpack that we’ve needed to protect and insulate the glaciers during the summer. “The window has gotten shorter and shorter, and we've had fewer and fewer storms within that window."
"Right now just about the entire south and west side of the mountain is totally bare and free of snow. I’ve worked here 20 years. My mother-in-law has grown up here her whole life and she said she's never seen it this bare,” says Meyers.
This extreme lack of snow has lead to more melting of the glaciers this summer and recent debris flows and lahars. With more future melting of the glaciers, more of these flows are likely along with impacts to hiking, fishing and groundwater. "Ground water is really important to the upper Sacramento River , including the McCloud River and the Shasta River which feeds into the Klamath River,” says Blaschak.
The Shasta-Trinity U.S. Forest Service says we need to see some healthy winters with a healthy snowpack to grow the glaciers, but it also needs to happen year over year. "We're kind of just maintaining at this point based on what I’ve seen over the last two decades," says Meyers. Blaschak explains, "if we keep seeing conditions like this, if we keep having further years where we have drought more often than not, more stretches of long periods of hot weather, just everything is more intense. These are all things that will continue to put pressure on the glaciers on Mt. Shasta."