If you’re visiting Alaska this year, you may get to experience a once-in-a-lifetime geologic event. A glacier in Denali National Park has started moving between 50 to 100 times faster than normal.
Last month, a pilot flying over Denali—a park home to the tallest mountain in the U.S.—spotted unusual topography around Muldrow Glacier and took photos of the uneven landscape to send to a geologist friend. Using the pilot’s tip, the National Park Service confirmed that the glacier, which sits near Denali (previously known as Mt. McKinley), is experiencing what’s known as a glacial surge event.
Glacial surges are “really strange events,” Jonny Kingslake, an assistant professor of environmental science at Columbia University, said in a video call. “They are these things that have fascinated glaciologists for decades.”
Anyone who’s been for a hike along a glacier may think of them as sedentary, but most of the world’s glaciers are constantly on the move, flowing at (very literal) glacial rates of millimeters per day and retreating and advancing with the seasons. In a normal glacial setup, Kingslake said, you’d see snowfall at the top of the glacier, melting or carving at the bottom, and then ice “flowing like a viscous material, like honey” between the two, keeping the glaciers in balance.
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But some glaciers—around 1% of the world’s glaciers, clustered in specific geographic areas like Alaska and parts of Tibet—experience cyclical periods where they move much faster than normal, followed by a period of rest. These periods are known as glacial surges, loosely defined as when a glacier picks up speed to at least 10 times its usual pace.
“The whole thing is flowing very slowly, and then suddenly it accelerates, and that can cause the glacier at higher elevations to thin, and then the ice slumps down to lower elevations,” Kingslake explained. “Then that happens, and it slows back down, and the material at lower elevations starts to melt, and the ice near the top thickens, and the whole thing repeats. It’s doing, like, a see-saw thing.”
Surges can mean big changes for the glaciers; the last time the Muldrow Glacier surged, in the 1950s, it moved 4 miles over a couple of months. Glacial surges can be disruptive to humans who live around or traverse glaciers on a regular basis. The NPS cautioned that Muldrow Glacier, which serves as a route up Denali for climbers, may no longer be transversable for the nearly 1,000 climbers who have signed up to climb Denali this year, as the surge creates new crevasses and jostles up the familiar landscape. (The NPS site has a pretty cool slide feature where you can compare before-and-after photos of the glacier.)
Glaciers are big, complex portions of the landscape, constantly being influenced by a variety of inputs. Because surges are such rare events, the science behind what causes them isn’t settled because researchers haven’t had a chance to pinpoint what, exactly, makes the glacial hydrology in some glaciers function in this stop-and-go manner. Experts have said that this particular surge event at the Muldrow Glacier is probably not connected to climate change. Geologic evidence suggests that the Muldrow has, in the past, experienced a surge roughly every 50 years (the last one was during the mid-1950s), and it was overdue for another.
But recent research suggests that meltwater, which often acts as a lubricant to help free ice, could have a role in creating glacial surges in some areas. In 2012, scientists witnessed what they called the “surge of the century” at the Austfonna ice cap, Europe’s largest ice field, which gushed enough water to fill 1.7 million Olympic swimming pools during one of its surge events that autumn. Based on their observations, researchers deduced that meltwater accumulated due to increasingly warm summers and was partially responsible for triggering this surge event.
And as climate change rapidly alters the landscape, glacial behavior also appears to be moving beyond surges and changing in worrisome ways. In 2002, a glacier in Russia traveled 11 miles (17.7 kilometers) in six minutes, reaching a speed of 150 mph (241.4 kph) as it crashed into a village and killed 100 people. The event was a new kind of behavior for a glacier and was dubbed by scientists as “a glacier-debris flow.” In 2016, two glaciers in Tibet showed signs of going through surges but then experienced collapses similar to the 2002 event. Scientists later partially linked the Tibetan collapses partially to climate change.
While Muldrow Glacier’s surge might be a routine event, even on our increasingly hotter planet, it highlights just how little we know about some of the world’s fastest-changing areas.
“The reason we don’t understand [surges] is because they’re rare events, they happen over decades, and many of these places we haven’t actually been studying for decades,” Kingslake said. “Even with all the technology you can imagine, these are very difficult places to study.”