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Mt. Shasta’s Glaciers are Disappearing

The big melt this summer garnered headlines, but it isn't a new phenomenon: Glaciologists have been watching California's alpine glaciers shrink for decades.

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The data is in, and it’s damning: Shasta’s glaciers are dying. Climate change has brought drought, high temps, and unseasonable heat waves to the California mountains, and the ice just can’t take it.

“In today’s climate, the vast majority of glaciers in the lower 48 will disappear,” says glaciologist Mauri Pelto, who has been studying the glaciers of the west coast mountain ranges for several years. “they’re all telling the same story right now, they’re all losing volume.”

Dr. Pelto and his team have spent the last 32 years studying the behavior of coastal range glaciers and the effect of glacial retreat on the rest of the ecosystem. The group he has directed since 1984, the North Cascades Glacier Climate Project, monitors the behavior of more glaciers than any other on the continent. 

Headlines aside, Pelto says that this year’s drastic melt on Shasta wasn’t that much of an anomaly. That’s bad news.

“It was the worst year, but 2018 wasn’t that far off.” The heat wave that hit the PNW in late June was historically unusual, but the rest of the summer “wasn’t that exceptional”. As climate change accelerates, these hot and smoky summers will become the norm, not the exception, he adds, and the glaciers that so characterize many of the country’s tallest mountains will become nothing but memory.

A glacier is a flowing, changing river of ice. Alpine glaciers (those found in the mountains, as opposed to continental ice sheets) flow downhill, with the rate controlled by the slope, the amount of meltwater “greasing” the bottom of the glacier, and the type of ground underneath the ice. They form when snow begins to stay in an area year-round—a mountain-top, a hanging valley—and continues accumulating over successive winters. The weight of the snow begins to compress the lower layers into firn, a state between snow and ice where the snow has recrystallized into approximately the size and shape of sugar crystals and become much more dense, but hasn’t yet completed the transition to ice. Gradually, the crushing weight of the snow squeezes the remaining air out of the lowest layers of the building glacier, and the firn completes its transformation to ice.

A glacier can be divided into three zones: the accumulation zone, the equilibrium line, and the ablation zone. In the accumulation zone, more snow falls than melts, increasing glacial mass. In the ablation zone, more snow melts than falls, shrinking glacial mass. The equilibrium line, where snowfall and snowmelt are equal, separates the two. As the equilibrium line moves upwards, shrinking the accumulation zone (for example, when the average temperature at the glacier’s elevation increases due to climate change or a long drought reduces the amount of snowfall to the glacier’s surface), the glacier begins to shrink, too; more of it is melting than forming new ice.

White blankets protecting Rhone Glacier from extreme melting due to global warming, Gletsch, canton of Valais, Switzerland
White blankets protecting Rhone Glacier from extreme melting due to global warming, Gletsch, canton of Valais, Switzerland (Photo: Roberto Moiola / Sysaworld/Moment via Getty Images)

“To survive, a glacier has to have a consistent accumulation zone,” says Dr. Pelto. Some glaciers get most of their mass from actual snowfall, while some, including many on Shasta, rely on winddrift or avalanches for new mass.

Besides the aesthetic value for hikers and backpackers, the loss of a glacier causes a whole ripple effect of consequences throughout its ecosystem. A recent study by Dr. Pelto and his team showed that the hydrology of rivers and streams in the glacier’s basin will change as glacial runoff disappears as a source of water. This runoff is most important during the lowest seasonal flow, in late summer, when the snow is all gone and rain is scarce; the glacial runoff also decreases water temperature during that time, often the hottest of the entire summer. 

While that increase may be too small for people to notice, even a small rise in stream temperature can alter the entire fish community of a stream, and many trout and salmon native to the coastal mountains can’t tolerate higher temperatures. In addition, on Shasta, the loose debris that was once underneath or on top of the glaciers presents a serious danger. 

“That [sediment] is really easily incorporated into debris flow,” says Dr. Pelto. The chance of such flows starting with hikers on the mountain is a serious concern for the Forest Service, which manages most of the trails in the area. 

So what happened on Mt. Shasta this year?

“The current climate regime of California isn’t suitable for glaciers to exist anymore,” Dr. Pelto says. Nowhere was that more obvious this year than Mt. Shasta, which by late in the summer was practically bare of snow. April had 60-75% percent of the normal snowpack at most monitoring stations, but early summer heat meant that dropped to just 20-25% by early May, and by July nearly the entire glacier was bare of snow. 

No snow means no accumulation zones, which means shrinking glaciers, and over the summer of 2021 the peak’s glaciers may have lost a fifth of their mass in this summer alone. Before the summer of 2021 they had already lost half of the area they covered almost 16 years ago; with this year’s retreat, the longest glacier, Whitney Glacier, actually fractured, and the smaller remnant left by the break is not expected to survive the season. 

For Mt. Shasta’s iconic glaciers, says Dr. Pelto, “it’s a matter of when, not if, they melt away.” Some of the world’s other alpine glaciers might have a chance, if we take drastic action to curtail climate change; they’ll shrink, but they may not disappear. Farther north of the equator, too, the chances are better, where temperatures are lower and droughts less prolific. But Shasta’s glaciers are not expected to survive our current climate, and the change already made to the atmosphere and global temperatures is unlikely to be reversed in time to save them. Enjoy them while you can.