Alaska’s melting glaciers may have set the stage for a 7.8 magnitude earthquake in 1958 that triggered a massive avalanche of approximately 90 million tons of rock into the narrow inlet of Lituya Bay.
A new study from the Geophysical Institute at the University of Alaska, Fairbanks, found that ice loss affected the timing and location of earthquakes magnitude 5.0 or greater in the area over the past century.
Alaska is home to some of the largest glaciers in the world, weighing thousands of pounds and sinking the land below.
When these giant glaciers begin to melt, the once-sunken land quickly ricochets off and tectonic plates grind past each other, causing a seismic event.
Alaska’s melting glaciers may have created the conditions for a 7.8 magnitude earthquake (picture) in 1958, which triggered a massive avalanche of around 90 million tons of rock into the narrow inlet of Lituya Bay
Scientists have long feared Alaska’s melting glacier could trigger catastrophic natural disasters like massive avalanches and landslides, but few have thought of earthquakes.
However, it is known that ice loss caused the events in otherwise tectonically stable regions such as interior Canada and Scandinavia.
In Alaska, this pattern was harder to spot because earthquakes are common in the southern part of the state.
This region is home to massive glaciers several thousand feet thick that cover hundreds of square miles.
The team found that there is a link between the growing movements of the mantle and the massive earthquakes in Southeast Alaska, where glaciers have been melting for more than 200 years
And with so much weight, the land sinks under it.
When the ice slowly disappears due to the warmer temperatures than usual, the soil rebounds like a sponge, moving the entire mantle.
Chris Rollins, the lead study author who conducted the research at the Geophysical Institute, said, “Uplift has two components.”
“There is the so-called ‘elastic effect’ in which the earth immediately pops up again after a mass of ice has been removed.”
“Then there is the lingering effect of the mantle flowing back up under the vacated space.”
The team found that there is a link between the growing movements of the mantle and the massive earthquakes in Southeast Alaska, where glaciers have been melting for more than 200 years.
Southern Alaska lies on the border between the continental North American plate and the Pacific plate, which has lost more than 1,200 cubic miles of ice.
The researchers found that the plates dragged past each other at a rate of about two inches per year – about twice as fast as the San Andreas Fault in California – causing frequent earthquakes.
However, the disappearance of glaciers has also caused the land in southeastern Alaska to grow about 1.5 inches per year.
Rollins had models of earth movement and ice loss since 1770 and found a subtle but unmistakable correlation between earthquakes and earth impacts.
When they combined their ice loss and shear stress maps with seismic records from 1920, they found that most major quakes correlated with long-term earth impact stress.
Southern Alaska lies on the border between the continental North American plate and the Pacific plate, which has lost more than 1,200 cubic miles of ice
Unexpectedly, the greatest ice loss stress occurred near the exact epicenter of the 1958 quake that caused the Lituya Bay tsunami.
While glacier melting is not a direct cause of earthquakes, it likely modulates both the timing and severity of seismic events.
When the earth rebounds after a glacier retreats, it resembles the rise of bread in an oven and spreads in all directions.
This effectively resolves strike slip errors like the Fairweather in Southeast Alaska and makes it easier for both sides to slip past each other.
In the case of the 1958 quake, the postglacial rebound rotated the crust around the fault in a way that added stress near the epicenter as well.
Both this and the relaxation effect brought the fault closer to failure.
“The movement of the plates is the main driver of seismicity, uplift and deformation in the region,” said Rollins.
“But the postglacial rebound contributes to it, much like the de-icing on the cake. It is more likely that faults in the red zone will reach their loading limit and slip in an earthquake. ‘