American scientists have carried out a detailed seismic survey of the Earth's interior beneath Patagonia. They concluded that the rapid melting of glaciers in the region had increased tectonic activity beneath the continent, causing the Earth's surface to rise.
The hundreds of kilometres of glaciers covering the Andes in Chile and Argentina are now melting at one of the fastest rates on the planet. The land the ice was hiding is shifting and rising fast as they disappear. Scientists at Washington University in St Louis, USA, have found a link between the loss of ice mass, rapid rock uplift and tectonic plate faulting beneath Patagonia. Their seismic results are published in the journal Geophysical Research Letters.
Patagonia is a mountainous region in southern South America. Because population density there is low and the risk of earthquakes is fairly low, scientists have done little seismic research in the region.
Now, researchers have turned their attention to the fact that changes in the size of glaciers and the structure of the mantle are causing rocks to rise rapidly. New seismic data have shown how a fault in a dipping tectonic plate, which lies about 97 kilometres beneath Patagonia, allows the hot and liquid mantle to flow beneath South America.
When the glaciers above the rift melt, the mass of ice ceases to press on the rocks, so the mantle beneath loses viscosity and the lithosphere thins. Many changes in Patagonia's topography are related to these factors, including the rapid uplift of some previously ice-covered areas.
Scientists have found the hottest and most fluid mantle in the rift region, above which the ice has only recently disappeared. It also turned out that the viscosity of the mantle in southern Patagonia is higher than in the north, so the rate of rock uplift increases from south to north. Consequently, scientists believe that over time the mantle dynamics associated with the faulting will increase even more.
A study of plate tectonics is needed to better understand the response of rocks to glaciation and its extinction. More accurate models will enable a better reconstruction of recent changes in ice sheets around the world caused by global warming.
In addition, the vast amount of water released from melted glaciers flows into the ocean, land movement influences this process and must therefore be taken into account when predicting global sea levels.
