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Pine Island Glacier (PIG) is a large
ice stream An ice stream is a region of fast-moving ice within an ice sheet. It is a type of glacier, a body of ice that moves under its own weight. They can move upwards of a year, and can be up to in width, and hundreds of kilometers in length. They t ...
, 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 The Hudson Mountains are a mountain range in western Ellsworth Land just east of Cranton Bay and Pine Island Bay at the eastern extremity of Amundsen Sea. They are of volcanic origin, consisting of low scattered mountains and nunataks that pro ...
into
Pine Island Bay The Amundsen Sea, an arm of the Southern Ocean off Marie Byrd Land in western Antarctica, lies between Cape Flying Fish (the northwestern tip of Thurston Island) to the east and Cape Dart on Siple Island to the west. Cape Flying Fish marks the ...
, Amundsen Sea,
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
. It was mapped by the
United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
(USGS) from surveys and
United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
(USN) air photos, 1960–66, and named by the
Advisory Committee on Antarctic Names The Advisory Committee on Antarctic Names (ACAN or US-ACAN) is an advisory committee of the United States Board on Geographic Names responsible for recommending commemorative names for features in Antarctica. History The committee was established ...
(US-ACAN) in association with Pine Island Bay. The area drained by Pine Island Glacier comprises about 10% of the
West Antarctic Ice Sheet The Western Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. The WAIS is classified as ...
. 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 An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...
about twice the size of
Washington, DC ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan ...
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 The Rothera Research Station is a British Antarctic Survey (BAS) base on the Antarctic Peninsula, located at Rothera Point, Adelaide Island. Rothera also serves as the capital of the British Antarctic Territory, a British Overseas Territo ...
, nearly away. The area is not
claimed "Claimed" is the eleventh episode of the The Walking Dead (season 4), fourth season of the Apocalyptic and post-apocalyptic fiction, post-apocalyptic Horror fiction, horror television series ''The Walking Dead (TV series), The Walking Dead'', wh ...
by any nations and the
Antarctic Treaty russian: link=no, Договор об Антарктике es, link=no, Tratado Antártico , name = Antarctic Treaty System , image = Flag of the Antarctic Treaty.svgborder , image_width = 180px , caption ...
prohibits any new claims while it is in force.


Ice sheet drainage

The
Antarctic ice sheet The Antarctic ice sheet is one of the two polar ice caps of Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth, with an average thickness of over 2 kilometers. It covers an area of almost and ...
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 The East Antarctic Ice Sheet (EAIS) is one of two large ice sheets in Antarctica, and the largest on the entire planet. The EAIS lies between 45° west and 168° east longitudinally. The EAIS holds enough ice to raise global sea levels by and ...
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 The Ross Ice Shelf is the largest ice shelf of Antarctica (, an area of roughly and about across: about the size of France). It is several hundred metres thick. The nearly vertical ice front to the open sea is more than long, and between hi ...
, 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 The Amundsen Sea, an arm of the Southern Ocean off Marie Byrd Land in western Antarctica, lies between Cape Flying Fish (the northwestern tip of Thurston Island) to the east and Cape Dart on Siple Island to the west. Cape Flying Fish marks th ...
. 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 stream An ice stream is a region of fast-moving ice within an ice sheet. It is a type of glacier, a body of ice that moves under its own weight. They can move upwards of a year, and can be up to in width, and hundreds of kilometers in length. They t ...
s. 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 The Western Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. The WAIS is classified as ...
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 An ice shelf is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland, Northern Canada, and the Russian Arctic. The b ...
. 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 Circumpolar Deep Water (CDW) is a designation given to the water mass in the Pacific and Indian oceans that is a mixing of other water masses in the region. It is characteristically warmer and saltier than the surrounding water masses, causing CD ...
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 In physics, a mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have bee ...
of 46 
gigatonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
s per year, which is equivalent to per year global
sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
. 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 The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
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 The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
, 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 The British Antarctic Survey (BAS) is the United Kingdom's national polar research institute. It has a dual purpose, to conduct polar science, enabling better understanding of global issues, and to provide an active presence in the Antarctic on ...
(BAS) scientists reported that 2,200 years ago a
volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...
erupted under the
Antarctic ice sheet The Antarctic ice sheet is one of the two polar ice caps of Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth, with an average thickness of over 2 kilometers. It covers an area of almost and ...
. This was the biggest Antarctic eruption in the last 10,000 years. The volcano is situated in the
Hudson Mountains The Hudson Mountains are a mountain range in western Ellsworth Land just east of Cranton Bay and Pine Island Bay at the eastern extremity of Amundsen Sea. They are of volcanic origin, consisting of low scattered mountains and nunataks that pro ...
, close to Pine Island Glacier. The eruption spread a layer of
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
and
tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they rem ...
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 core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ic ...
s. 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 concluding that the bedrock below WAIS was uplifted at a higher rate than previously thought, the authors suggested this could eventually help to stabilize the ice sheet.


History of fieldwork


On the ice

Due to the remoteness of Pine Island Glacier, most of the information available on the ice stream comes from airborne or satellite-based measurements. The first expedition to visit the ice stream was a United States over-snow traverse, which spent around a week in the area of PIG during January 1961. They dug snow pits to measure snow accumulation and carried out seismic surveys to measure ice thickness. One of the scientists on this traverse was
Charles R. Bentley Charles Raymond Bentley (December 23, 1929 – August 19, 2017) was an American glaciologist and geophysicist, born in Rochester, New York. He was a professor emeritus at the University of Wisconsin–Madison. Mount Bentley and the Bentley Su ...
, who said "we didn't know we were crossing a glacier at the time." PIG is around wide at the point visited and at ground level cannot be visually distinguished from the surrounding ice. This expedition was called the "Ellsworth Highland Traverse". In the 2004–2005 field season a team of nine, using a British Antarctic Survey (BAS)
Twin Otter The de Havilland Canada DHC-6 Twin Otter is a Canadian STOL (Short Takeoff and Landing) utility aircraft developed by de Havilland Canada, which produced the aircraft from 1965 to 1988; Viking Air purchased the type certificate, then restarted ...
aircraft equipped with ice-penetrating radar, completed an aerial survey of PIG and its adjacent ice sheet. The team of seven British and two Americans flew 30 km grid patterns over the PIG until January 5, mapping the sub-glacial terrain of an area roughly the size of Nevada. Due to the remoteness of PIG and the logistical difficulties of caching enough fuel for the 2004–05 expedition and future project(s), BAS used the resources of the United States Antarctic Program (USAP) and their ski-equipped LC130 aircraft. After many weeks of weather delays the first four men arrived from
McMurdo Station McMurdo Station is a United States Antarctic research station on the south tip of Ross Island, which is in the New Zealand-claimed Ross Dependency on the shore of McMurdo Sound in Antarctica. It is operated by the United States through the Unit ...
on 9 November 2004, and began to establish camp and build a skiway for the C130s. The remaining members of the team arrived from Rothera Research Station 10 days later in a Twin Otter. Because of unusually good weather in the area that season the survey completed flying their grids by mid-January, and began flying 15 km grids of
Thwaites Glacier Thwaites Glacier, nicknamed the Doomsday Glacier, is an unusually broad and vast Antarctic glacier flowing into Pine Island Bay, part of the Amundsen Sea, east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. Its surface speeds excee ...
for a USAP expedition who had been experiencing unusually poor weather in their area that year. Flying over Antarctica's Pine Island Glacier on October 14, 2011 in a
DC-8 The Douglas DC-8 (sometimes McDonnell Douglas DC-8) is a long-range narrow-body airliner built by the American Douglas Aircraft Company. After losing the May 1954 US Air Force tanker competition to the Boeing KC-135, Douglas announced in Ju ...
research plane, scientists participating in NASA's IceBridge mission discovered a massive crack running about across the glacier's floating tongue. The rift is wide on average and deep. Another team from the
British Antarctic Survey The British Antarctic Survey (BAS) is the United Kingdom's national polar research institute. It has a dual purpose, to conduct polar science, enabling better understanding of global issues, and to provide an active presence in the Antarctic on ...
arrived at the ice stream on 8 December 2006 for the first of two field seasons. In the second field season, they spent three months there from November 2007 to February 2008. Work on the glacier included
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
measurements and seismic surveys. In January 2008 Bob Bindschadler of
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
landed on the floating
ice shelf An ice shelf is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland, Northern Canada, and the Russian Arctic. The b ...
of PIG, the first ever landing on this ice shelf, for a reconnaissance mission to investigate the feasibility of drilling through around of ice, to lower instruments into the ocean cavity below. It was decided that the small
crevasse A crevasse is a deep crack, that forms in a glacier or ice sheet that can be a few inches across to over 40 feet. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pie ...
free area was too hard for further landings and so further fieldwork had to be postponed. Therefore, two
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
(GPS) units and a weather station were positioned as near as possible to PIG. In the 2011–2012 field season, after five weeks of delays, the camp staff was finally able to establish the Main Camp just before New Year. The following week, Bindschadler and his team were able to arrive. Due to additional weather delays, the helicopters were not able to arrive by the NSF 'drop dead' date and the field season was cancelled. Limited science was still accomplished by the team thanks to a series of flights by KBA back onto the glacier; conditions had changed drastically since the last Twin Otter flights.NASA.gov
/ref> The
British Antarctic Survey The British Antarctic Survey (BAS) is the United Kingdom's national polar research institute. It has a dual purpose, to conduct polar science, enabling better understanding of global issues, and to provide an active presence in the Antarctic on ...
deployed a small team of four during the 2011–12 summer field season to carry out a series of seismic and radar surveys on PIG. They also installed a series of overwintering GPS stations. During the season, a separate BAS team travelled to the field party's location and installed an overwintering autonomous
VLF Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30  kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave a ...
station. This was followed by a radar traverse upstream using
snowmobile A snowmobile, also known as a Ski-Doo, snowmachine, sled, motor sled, motor sledge, skimobile, or snow scooter, is a motorized vehicle designed for winter travel and recreation on snow. It is designed to be operated on snow and ice and does not ...
s. This survey linked previous radar lines.


From the sea

The first ship to reach Pine Island Glacier's ice shelf, in Pine Island Bay, was the '' USS/USCGC Glacier'' in 1985. This ship was an icebreaker operated by the U.S. Coast Guard. The mission, known as ''Deep Freeze'', had scientists on board who took sediment samples from the ocean floor. During the summer field season, over two months from January to February 2009, researchers aboard the
U.S. Antarctic Program The United States Antarctic Program (or USAP; formerly known as the United States Antarctic Research Program or USARP and the United States Antarctic Service or USAS) is an organization of the United States government which has presence in the A ...
research vessel '' Nathaniel B. Palmer'' reached the ice shelf. This was the second time that the ''Palmer'' had successfully made it up to the glacier, the first time being in 1994. In collaboration with the British, the scientists used a robotic submarine to explore the glacier-carved channels on the continental shelf as well as the cavity below the ice shelf and glacier. The submarine, known as ''Autosub 3'', was developed and built at the
National Oceanography Centre The National Oceanography Centre (NOC) is a marine science research and technology institution based on two sites in Southampton and Liverpool, United Kingdom. It is the UK’s largest institution for integrated sea level science, coastal and d ...
in the UK. It completed six successful missions, travelling a total of under the ice shelf. Autosub is able to map the base of the ice shelf as well as the ocean floor and take various measurements and samples of the water on the way. The success of ''Autosub 3'' was particularly notable because its predecessor Autosub 2 was lost beneath the
Fimbul Ice Shelf The Fimbul Ice Shelf is an Antarctic ice shelf about long and wide, nourished by Jutulstraumen Glacier, bordering the coast of Queen Maud Land from 3°W to 3°E. It was photographed from the air by the Third German Antarctic Expedition (1938 ...
on only its second such mission.


See also

*
List of Antarctic ice streams This is a list of Antarctic ice streams. A complete list of Antarctic ice streams is not available. Names and locations of Antarctic ice features, including those listed below, can be found in the Scientific Committee on Antarctic Research The ...
*
List of glaciers in the Antarctic There are many glaciers in the Antarctic. This set of lists does not include ice sheets, ice caps or ice fields, such as the Antarctic ice sheet, but includes glacial features that are defined by their flow, rather than general bodies of ice. Th ...
*
Sif Island Sif Island is an island in Pine Island Bay of the Amundsen Sea, in Antarctica. It is long and consists of potassium feldspar granite, mostly covered in ice. It was discovered in February 2020 after the Pine Island Glacier melted away from arou ...


References


External links


Geo-temporal-spatial map
of research publications on PIG and surrounding area
NASA Earth Observatory: ''Images of Pine Island Glacier''

NASA Earth Observatory: ''Channel Beneath Pine Island Glacier''
{{Good article West Antarctica Ice streams of Antarctica Articles containing video clips