Melting glaciers in Alaska contributes to earthquakes, according to a new study. The researchers determined that ice loss in the 19th century laid the groundwork for a devastating earthquake in Lituya Bay in 1958.
The 7.8 magnitude earthquake triggered a rockslide and created a tsunami that ran 1,700 feet up a mountainside before plummeting back out into the sea.
According to scientists at the University of Alaska Fairbanks, ice loss near Glacier Bay National Park has influenced the timing and location of nearby earthquakes with a magnitude of 5.0 or greater during the past century.
While it was already known that melting glaciers cause earthquakes in otherwise tectonically stable regions, such as Canada’s interior and Scandinavia, this pattern has been harder to detect in Alaska.
Some of the world’s largest glaciers can be found in Alaska. These glaciers can be up to thousands of feet thick and cover hundreds of square miles.
The weight of the ice causes the land beneath it to sink, and the ground springs back like a sponge when the ice melts. The disappearance of glaciers has caused Southeast Alaska’s land to rise at about 1.5 inches per year.
“There are two components to the uplift,” said study lead author Chris Rollins. “There’s what’s called the ‘elastic effect,’ which is when the earth instantly springs back up after an ice mass is removed. Then there’s the prolonged effect from the mantle flowing back upwards under the vacated space.”
The research links the expanding movement of the mantle with large earthquakes across Southeast Alaska, where glaciers have been melting for over 200 years.
Based on models of Earth movement and ice loss since 1770, the researchers identified a clear correlation between earthquakes and Earth rebound.
Maps of ice loss and seismic records dating back to 1920 showed that most large earthquakes coincided with the stress from long-term Earth rebound.
In the case of the 1958 earthquake, the postglacial rebound molded the crust around the fault in a way that increased stress near the epicenter.
“The movement of plates is the main driver of seismicity, uplift and deformation in the area,” said Rollins. “But postglacial rebound adds to it, sort of like the de-icing on the cake. It makes it more likely for faults that are in the red zone to hit their stress limit and slip in an earthquake.”
The study is published in the journal JGR Solid Earth.
By Chrissy Sexton, Earth.com Staff Writer