Retreating glaciers spur Alaskan earthquakes
NASA and USGS scientists have found that retreating glaciers in
southern Alaska may be opening the way for future earthquakes.
The study examined the likelihood of increased earthquake activity
in southern Alaska as a result of rapidly melting glaciers. As glaciers melt they lighten the
load on the Earth's crust. Tectonic plates, that are mobile pieces of the Earth's crust, can
then move more freely.
Historically, when big ice masses started to retreat, the number
of earthquakes increased. More than 10,000 years ago, at the end of the great
ice age, big earthquakes occurred in Scandinavia as the large glaciers began to melt. In
Canada, many more moderate earthquakes occurred as ice sheets melted.
Southern Alaskan glaciers are very sensitive to climate change,
Sauber added. Many glaciers have shrunk or disappeared over the last 100 years. The trend,
which appears to be accelerating, seems to be caused by higher temperatures and changes in
In southern Alaska, a tectonic plate under the Pacific Ocean is
pushing into the coast, which creates very steep mountains. The high mountains and heavy
precipitation are critical for glacier formation. The colliding plates create a great deal
of pressure that builds up, and eventually is relieved by earthquakes.
The weight of a large glacier on top of these active earthquake
areas can help keep things stable. But, as the glaciers melt and their load on the plate
lessens, there is a greater likelihood of an earthquake happening to relieve the large strain
Even though shrinking glaciers make it easier for earthquakes to
occur, the forcing together of tectonic plates is the main reason behind major earthquakes.
The researchers believe that a 1979 earthquake in southern Alaska,
called the St. Elias earthquake, was promoted by wasting glaciers in the area. The earthquake
had a magnitude of 7.2 on the Richter scale.
Along the fault zone, in the region of the St. Elias earthquake,
pressure from the Pacific plate sliding under the continental plate had built up since 1899
when previous earthquakes occurred. Between 1899 and 1979, many glaciers near the fault zone
thinned by hundreds of meters and some completely disappeared.