Like many other glaciers, the Amalia Glacier in the southern Patagonian ice field has lost enormous amounts of ice in recent decades: its tongue has retreated by more than ten kilometers in the past 100 years. Hardly any other glacier in the region disappeared as quickly. But after 2019, the trend only reversed and the later melting slowed down for an unusual reason, as Maximillian Van Wyk de Vries from the University of Minnesota in Minneapolis and his team write in »Geology«: A landslide stabilized the glacier.
Landslides occur more frequently in the vicinity of glaciers: on the one hand, the ice tongues can make slopes steeper and, on the other hand, they also make them more stable because they form a kind of abutment. If the body of ice disappears, there is no counterforce, so parts of the rock can fall. This sometimes has catastrophic consequences, as a case from India shows in February 2021, in which more than 100 people died and infrastructure in a valley was destroyed.
Fortunately, no one was injured in Chile when 262 million cubic meters of rock and debris fell onto the ice. However, the glacier responded immediately: its glacial tongue advanced rapidly after previously retreating relatively steadily. The ice tongue has grown again by more than 1000 meters. However, the initially greatly increased flow rate has once again decreased significantly, and the Amalia Glacier is now only flowing towards the sea at half the rate it was before the event.
First the landslide had pushed the ice downstream, so the glacier immediately advanced and increased in size. Over time, sediments and rocks from the landslide were then deposited where the glacier meets the ocean. This prevented icebergs from breaking off into the sea, effectively stabilizing the ice tongue. However, it is unclear how long this effect lasts and whether the decline will start again at an accelerated rate afterwards.