Pine Island Glacier

Pine Island Glacier (PIG) is a large ice stream, and the fastest melting glacier in Antarctica, responsible for about 25% of Antarctica's ice loss. The glacier ice streams flow west-northwest along the south side of the Hudson Mountains into Pine Island Bay, Amundsen Sea, Antarctica. It was mapped by the United States Geological Survey (USGS) from surveys and United States Navy (USN) air photos, 1960–66, and named by the Advisory Committee on Antarctic Names (US-ACAN) in association with Pine Island Bay.

The area drained by Pine Island Glacier comprises about 10% of the West Antarctic Ice Sheet. Satellite measurements have shown that the Pine Island Glacier Basin has a greater net contribution of ice to the sea than any other ice drainage basin in the world and this has increased due to recent acceleration of the ice stream.

An iceberg about twice the size of Washington, DC broke off from the glacier in February 2020. Pine Island Glacier's ice velocity has accelerated to over 33 feet per day.

The ice stream is extremely remote, with the nearest continually occupied research station at Rothera, nearly away. The area is not claimed by any nations and the Antarctic Treaty prohibits any new claims while it is in force.

Ice sheet drainage

The Antarctic ice sheet is the largest mass of ice on earth, containing a volume of water equivalent to of global sea level. The ice sheet forms from snow which falls onto the continent and compacts under its own weight. The ice then moves under its own weight toward the edges of the continent. Most of this transport to the sea is by ice streams (faster moving channels of ice surrounded by slower moving ''ice walls'') and outlet glaciers. The Antarctic ice sheet consists of the large, relatively stable, East Antarctic Ice Sheet and a smaller, less stable, West Antarctic Ice Sheet. The West Antarctic Ice Sheet is drained into the sea by several large ice streams, most of which flow into either Ross Ice Shelf, or Filchner-Ronne Ice Shelf. Pine Island and Thwaites Glaciers are two major West Antarctic ice streams which do not flow into a large ice shelf. They are part of an area called the Amundsen Sea Embayment. A total area of , 10 percent of the West Antarctic Ice Sheet, drains out to the sea via Pine Island Glacier, this area is known as the Pine Island Glacier drainage basin.

Weak underbelly of the West Antarctic Ice Sheet

The Pine Island and Thwaites glaciers are two of Antarctica's five largest ice streams. Scientists have found that the flow of these ice streams has accelerated in recent years, and suggested that if they were to melt, global sea levels would rise by , destabilising the entire West Antarctic Ice Sheet and perhaps sections of the East Antarctic Ice Sheet.

In 1981 Terry Hughes proposed that the region around Pine Island Bay may be a "weak underbelly" of the West Antarctic Ice Sheet. This is based on the fact that, unlike the majority of the large West Antarctic ice streams, those flowing into the Amundsen Sea are not protected from the ocean by large floating ice shelves. Also, although the surface of the glacier is above sea level, the base lies below sea level and slopes downward inland, this suggests that there is no geological barrier to stop a retreat of the ice once it has started.

Acceleration and thinning

The Pine Island glacier began to retreat in the 1940s. Prior to this retreat, the grounding line of Pine Island Glacier was located on a prominent seabed ridge. This ridge now acts as a barrier, restricting the amount of relatively warm circumpolar deep water that can reach the thickest ice.

The speed of Pine Island Glacier increased by 77 percent from 1974 to the end of 2013, with half of this increase occurring between 2003 and 2009. This speed up has meant that by the end of 2007 the Pine Island Glacier system had a negative mass balance of 46 gigatonnes per year, which is equivalent to per year global sea level rise. In other words, much more water was being put into the sea by PIG than was being replaced by snowfall. Measurements along the centre of the ice stream by GPS demonstrated that this acceleration is still high nearly inland, at around 4 percent over 2007. It has been suggested that this recent acceleration could have been triggered by warm ocean waters at the end of PIG, where it has a floating section (ice shelf) approximately long. It has also been shown that PIG underwent rapid thinning during the Holocene, and that this process may continue for centuries after it is initiated.

As the ice stream accelerates it is also getting steeper. The rate of thinning within the central trunk has quadrupled from 1995 to 2006. If the current rate of acceleration were to continue the main trunk of the glacier could be afloat within 100 years.

The ice front stayed in a more or less stable position from 1973 to 2014, with a 10 km retreat in 2015.

Subglacial volcano

In January 2008, British Antarctic Survey (BAS) scientists reported that 2,200 years ago a volcano erupted under the Antarctic ice sheet. This was the biggest Antarctic eruption in the last 10,000 years. The volcano is situated in the Hudson Mountains, close to Pine Island Glacier. The eruption spread a layer of volcanic ash and tephra over the surface of the ice sheet. This ash was then buried under the snow and ice. The date of the eruption was estimated from the depth of burial of the ash. This method uses dates calculated from nearby ice cores. The presence of the volcano raises the possibility that volcanic activity could have contributed, or may contribute in the future, to increases in the flow of the glacier. In 2018 it was found that there is a substantial volcanic heat source beneath Pine Island Glacier approximately half as large as the active Grimsvötn volcano on Iceland. The same year a study was published con