Thwaites Glacier

Thwaites Glacier is an unusually broad and vast Antarctic glacier located east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. It was initially sighted by polar researchers in 1940, mapped in 1959–1966 and officially named in 1967, after the late American glaciologist Fredrik T. Thwaites.[1][3] The glacier flows into Pine Island Bay, part of the Amundsen Sea, at surface speeds which exceed 2 kilometres (1.2 mi) per year near its grounding line. Its fastest-flowing grounded ice is centered between 50 and 100 kilometres (31 and 62 mi) east of Mount Murphy.[1] Like many other parts of the cryosphere, it has been adversely affected by climate change, and provides one of the more notable examples of the retreat of glaciers since 1850. Thwaites Glacier is closely monitored for its potential to elevate sea levels.[4] Since the 1980s, Thwaites and Pine Island Glacier have been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, in part because they seem vulnerable to irreversible retreat and collapse even under relatively little warming, yet also because if they go, the entire ice sheet is likely to eventually follow.[5][6][7] This hypothesis is based on both theoretical studies of the stability of marine ice sheets and observations of large changes on these two glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces have lowered, and their grounding lines have retreated.[8] They are believed very likely to eventually collapse even without any further warming.[9][10][11] The outsized danger Thwaites poses has led to some reporters nicknaming it the Doomsday Glacier,[12][13][14][15][16] although this nickname is controversial among scientists.[17] The Thwaites Ice Shelf, a floating ice shelf which braces and restrains the eastern portion of Thwaites Glacier, is likely to collapse within a decade from 2021.[5][18][19][20] The glacier's outflow is likely to accelerate substantially after the shelf's disappearance; while the outflow currently accounts for 4% of global sea level rise, it would quickly reach 5%, before accelerating further. The amount of ice from Thwaites likely to be lost in this century will only amount to several centimetres of sea level rise,[1][21] but its breakdown will rapidly accelerate in the 22nd and 23rd centuries,[10] and the volume of ice contained in the entire glacier can ultimately contribute 65 cm (25+1⁄2 in) to global sea level rise,[5] which is more than twice the total sea level rise to date.[22] Some researchers have proposed engineering interventions to stabilize the glacier,[10][23][24] but they are very new, costly and their success uncertain.[25] Location and featuresThwaites Glacier is located at the northern edge of the West Antarctic Ice Sheet, next to Pine Island Glacier. Both glaciers continually shed ice from their grounding line into Pine Island Bay, which is part of the Amundsen Sea. The fastest flows of ice occur between 50 and 100 kilometres (31 and 62 mi) east of Mount Murphy, where they can exceed 2 kilometres (1.2 mi) per year.[1] At 120 km (75 mi) in width,[2] Thwaites Glacier is the single widest glacier in the world, and it has an area of 192,000 km2 (74,000 sq mi). This makes it larger than the American state of Florida (170,000 km2 (66,000 sq mi)), and a little smaller than the entire island of Great Britain (209,000 square kilometres (81,000 square miles)). It is also very tall, with ice thickness from bedrock to surface measuring between 800 metres (2,624+1⁄2 ft) and 1,200 metres (3,937 ft).[1] Due to this immense size, enormous mass is shed when the repeated ice calving events occur at the glacier's marine terminus – the point where grounding line is in contact with water. The largest events, on the glacier's more vulnerable western side, are seismically detectable at ranges up to 1,600 km (990 mi).[27] The third Antarctic expedition of Richard E. Byrd in 1940 is believed to be first official sighting of the coastline of Thwaites. Detailed mapping of the glacier's surface took place between 1959 and 1966.[1] In 1967, it was officially named by the Advisory Committee on Antarctic Names after Fredrik T. Thwaites (1883–1961), who had never personally visited the glacier, but was a renowned glacial geologist, geomorphologist and professor emeritus at the University of Wisconsin–Madison.[3][28] McMurdo Station is used by researchers studying the glacier, such as the International Thwaites Glacier Collaboration (ITGC).[20] Thwaites Glacier Tongue and Thwaites Iceberg TongueThe Thwaites Glacier Tongue, or Western Glacier Tongue (75°0′S 106°50′W) was a narrow, floating part of the glacier, located about 30 mi (48 km) east of Mount Murphy.[28] It was the first part of the glacier to be mapped,[1] based on 65,000 aerial photographs collected during Operation Highjump in 1947. Back then, it was about 95 km (59 mi) long and 60 km (37 mi) wide.[30] By the time updated mapping took place during Operation Deepfreeze in 1967, the glacier tongue had advanced up to 75 km (47 mi) further north,[30] and had also experienced massive ice calving events which had produced Thwaites Iceberg Tongue (74°0′S 108°30′W),[31] a loose collection of icebergs occupying an area as large as 150 kilometres (93 mi) long and 35–65 kilometres (22–40 mi) wide at the time.[30] After breaking off from Thwaites Glacier Tongue, those icebergs ran aground in the Amundsen Sea, about 20 mi (32 km) northeast of Bear Peninsula. Initially, their southern extent was only 3 mi (4.8 km) north of Thwaites Glacier Tongue,[31] but as parts of the iceberg tongue continued to calve, it diminished in size (to 70 mi (110 km) long and 20 mi (32 km) wide.[31] By 1986, the entire iceberg tongue had rotated to the side and started to drift away, travelling 140 km (87 mi) west between 1986 and 1992.[30] Post-2010 break-up and current state Thwaites Glacier Tongue had also experienced destructive changes, eventually shortening to 40 mi (64 km) long and 20 mi (32 km) wide.[28] By 2012, it went from an ice tongue firmly attached to the rest of the glacier to a series of icebergs floating next to each other, each no larger than 1–5 kilometres (0.62–3.11 mi) in width and only held in place by sea ice. The final remainder of the old glacier tongue, with an area of 470 square kilometres (180 sq mi), disintegrated in 2016. This "melange" of icebergs is still referred to by its old name, as it continues to occupy a substantial amount of area and may retain a stabilizing effect on the glacier. However, future retreat of the surrounding sea ice is likely to trigger disintegration of ever-larger sections, like during the 2019 disintegration of icebergs on its western margin.[29] In 2023, scientists found that ice tongue retreat rates are subject to wide fluctuations after its break-up: over six years of observations, annual retreat accelerated by as much as 40% (from around 4 kilometres (2.5 mi) to 6 kilometres (3.7 mi) per year) twice, before slowing back down. These researchers have also repurposed a machine learning algorithm normally used in microbiology to identify crevasses in the remains of the ice tongue and project how they may affect its stability.[32][26]On 15 March 2002, a notable calving event took place, when the National Ice Center reported that an iceberg named B-22 broke off. This iceberg was about 85 km (53 mi) long by 65 km (40 mi) wide, with a total area of some 5,490 km2 (2,120 sq mi), comparable to Rhode Island.[33][15] While most of the iceberg broke up quickly, the largest piece, B-22A, with an area of around 3,000 km2 (1,158+1⁄2 sq mi) or "twice the size of Houston, Texas", drifted in the vicinity of the glacier even as the rest of the glacier tongue continued to break up. In 2012, it got stuck on seafloor, 53 km (33 mi) away from the ice tongue, where its presence had some stabilizing impact on the rest of the glacier. In October 2022, it finally started moving again, rapidly drifting to the northwest. It is likely to end up as one of the longest-lived icebergs in history.[34][15] Thwaites Ice ShelfGlaciers in Antarctica commonly have ice shelves, which are large bodies of sea ice that are permanently floating just offshore, and whose presence helps to stabilize the glacier. Though the Thwaites Ice Shelf has a width of 45 km (28 mi)[5] and a vertical thickness of at least 587 m (1,926 ft)),[35] it is relatively light for its size, and is stabilized by partially resting on an underwater mountain 50 km (31 mi) offshore.[2] While it only shields the eastern part of the glacier (with the western formerly covered by the Ice Tongue), its presence is already sufficient to counter large calving events on that side of the glacier. Under the hypothesis of marine ice cliff instability, ice cliffs at the edge of the glacier would end up unsustainably tall once this ice shelf fails and no longer buttresses them, leading to a chain reaction of collapse over centuries.[18][19][8] However, the accuracy of this hypothesis has been disputed in multiple papers,[36][37][38] and some research suggests that the loss of the ice shelf would result in almost no change to glacier's trajectory.[39] Subglacial featuresSwamp-like canal areas and streams underlie the glacier. The upstream swamp canals feed streams, while the dry areas between those streams retard flow of the glacier. Due to this friction, the glacier is considered stable in the short term.[41] As warming progresses, these streams expand and form larger structures underneath the glacier.[11] The largest one to date was discovered by NASA researchers in 2019 – an underwater cavity formed mostly in the previous three years, nearly 350 m (1,148+1⁄2 ft) tall and 4 km (2.5 mi) wide, with an area two-thirds the size of Manhattan.[42][43] In 2014, the area underneath Thwaites Glacier was found to have heat flow from geothermal activity nearly twice the global average, and about 3.5 times larger in hotspots.[44][45] By 2017, scientists have mapped 138 volcanoes beneath the West Antarctic Ice Sheet, with 91 of them previously unknown. Marie Byrd Land, the location of Thwaites and Pine Island Glaciers, was found to harbor around one volcano per every 11,200 km2 (4,300 sq mi) of area. This density is relatively high, though it is lower than in other global hotspots such as the East African Rift (one per 7,200 km2 (2,800 sq mi)) or even Antarctica's own central rift (one per 7,800 km2 (3,000 sq mi)). The heat from magma flows beneath these volcanoes can affect melting,[44][46] and the risk of volcano eruptions increases as more ice is lost as a consequence of isostatic rebound.[40] At the same time, both Marie Byrd Land and the central rift also contain the majority of West Antarctica's 29 volcanoes whose height exceeds 1 km (0.62 mi), even as they remain completely covered by ice. This massive size is likely to make them into significant roadblocks to ice flows, and thus gives them the potential to delay glacier retreat in its advanced stages.