Despite volcano-like rumbles deep beneath the mountain, Denali will not erupt soon. (Photo by Ned Rozell/UAF Geophysical Institute)
“These are volcanic-like earthquakes,” the type that happen when molten rock oozes beneath the surface, said Stephen Holtkamp, a researcher with the Alaska Earthquake Center. “They are right where volcanoes should be, right above the subducting slab at 100 kilometers depth.”
Mount Spurr, a volcano across Cook Inlet from Anchorage, erupted explosively in 1992. It hums all the time with earthquakes like the ones Holtkamp studied beneath Denali. Mount Spurr is on the southern end of what scientists call the Denali Gap, a 270-mile silent swath of the Alaska Range that could be pimpled with volcanoes but does not seem to be.
On the north end of the gap are two ponds filled with dark water near Healy. Volcanologists recognize these as maars, craters that formed when molten rock reached the water table and detonated. This event happened about 3,000 years ago, when the Iron Age began and the world held 50 million people, few of them near Healy. Rocks at the Buzzard Creek maars have the same chemical signature of Aleutian volcanoes.
As he looked back at more than a decade of Denali station data, Holtkamp found 200 similar volcano-like signals. So, is Denali about to erupt?
If Denali was a volcano, the mountain would show its hand with volcanic rocks on the surface as well as hot springs. As for the volcano-like earthquakes, Holtkamp said they don’t require the movement of molten rock, just active fluids passing through masses of rock.
“There might be magma, but only small packets,” he said. “It’s probably water coming from the slab (the Pacific plate, which is diving beneath the North American plate under Denali and most of Alaska). I think it’s evidence that fluids from the slab can migrate through the crust (the outermost shell of the planet).”
Given the uncertainty of science and the surprises the planet often delivers, does Holtkamp rule out the possibility of Denali someday expressing its inner volcano?
He would make that bet for our lifetimes and well beyond. But the workings beneath Denali might change to another state from the present “flat-slab subduction,” which makes the rock beneath the crust too cool to melt. That is millions of years in the future.
“A more traditional volcanic arc may emerge, but not necessarily at Denali,” Holtkamp said.
Since the late 1970s, the director of the Geophysical Institute at the University of Alaska Fairbanks has supported the writing and free distribution of this column to news media outlets. This is Ned Rozell’s 20th year as a science writer for the Geophysical Institute.