larsen c ice berg

Larsen C[edit source]

2016 rift in Larsen C, wide view

Glacier–ice shelf interactions.

As of July 2017^[update], Larsen C is the fourth largest ice shelf in Antarctica, with an area of about 44,200 km² (17,100 sq mi).^[18]
Satellite radar altimeter measurements show that between 1992 and 2001 the Larsen Ice Shelf lowered by up to 0.27 ± 0.11 meters per year.^[19] In 2004, a report concluded that although the remaining Larsen C region appeared to be relatively stable,^[20] continued warming could lead to its breakup within the following decade.^[21]
The breakaway process had begun by mid-2016.^[22][23] On 10 November 2016 scientists photographed the growing rift running along the Larsen C ice shelf,^[24] showing it running about 110 kilometres (68 mi) long with a width of more than 91 m (299 ft), and a depth of 500 m (1,600 ft). By December 2016, the rift had extended another 21 km (13 mi) to the point where only 20 km (12 mi) of unbroken ice remained and calving was considered to be a certainty in 2017.^[25] This was predicted to cause the collapse of between nine and twelve percent of the ice shelf, 6,000 km² (2,300 sq mi), an area greater than the US state of Delaware,^[18] or twice the size of Luxembourg.^[26] The calved fragment was predicted to be 350 m (1,150 ft) thick and to have an area of about 5,000 km² (1,900 sq mi).^[18] If the calved iceberg does not break into pieces, it will be among the largest icebergs ever recorded.^[25]
On 1 May 2017 members of MIDAS reported that satellite images showed a new crack, around 15 km (9 mi) long, branching off the main crack approximately 10 km (6 mi) behind the previous tip, heading toward the ice front.^[27] Scientists with Swansea University in the UK say the crack lengthened 18 km (11 mi) from 25 May to 31 May, and that less than 13 km (8 mi) of ice is all that prevents the birth of an enormous iceberg. "The rift tip appears also to have turned significantly towards the ice front, indicating that the time of calving is probably very close," Adrian Luckman and Martin O'Leary wrote on Wednesday in a blog post for the Impact of Melt on Ice Shelf Dynamics and Stability project, or MIDAS. "There appears to be very little to prevent the iceberg from breaking away completely." The larger swath of the Larsen C ice shelf that sat behind the calved iceberg "will be less stable than it was prior to the rift" and may rapidly disintegrate in the same manner as Larsen B did in 2002.^[28]
As of June 2017^[update] the speed of the imminent Larsen C iceberg was observed to be accelerating, with the eastern end moving at 10 metres (33 ft) per day away from the main shelf.^[29] As discussed by the Project MIDAS researchers on their site: “In another sign that the iceberg calving is imminent, the soon-to-be-iceberg part of Larsen C ice shelf has tripled in speed to more than 10 meters per day between 24 and 27 June 2017. The iceberg remains attached to the ice shelf, but its outer end is moving at the highest speed ever recorded on this ice shelf.”^[30]
On 7 July the Project MIDAS blog report stated: "The latest data from 6th July reveal that, in a release of built-up stresses, the rift branched several times. Using data from ESA's Sentinel-1 satellites, we can see that there are multiple rift tips now within 5 km (3.10 miles) of the ice edge. We expect that these rifts will lead to the formation of several smaller icebergs."^[31]

Imagery from NASA's Aqua MODIS showing the complete break of the ice shelf as of 12 July 2017

Photographic imagery from ESA's Sentinel-1B taken on 12 July 2017, showing the complete break

On 12 July 2017, Project MIDAS announced that a large, 5,800-square-kilometre (2,200 sq mi) portion of Larsen C had broken from the mainland at some point between 10 and 12 July.^[5][32] The iceberg, designated A-68, weighs more than a trillion tons^[33][34] and is more than 200 m (700 ft) thick.^[35] The final breakthrough was detected in data from NASA's Aqua MODIS satellite instrument, which images in the thermal infrared at a resolution of 1 kilometre (0.62 mi), and confirmed by NASA’s Suomi VIIRS instrument.^[36][36] The iceberg is not expected to be an immediate danger to shipping, but it could pose a threat if it moves significantly northwards.^[35]
Since the ice shelf is already floating, its departure from Antarctica will not affect global sea levels. However, a number of glaciers discharge onto it from the land behind the ice shelf, and may now flow faster due to the loss of support from the ice shelf. If all the ice that the Larsen C shelf currently holds back were to enter the sea, it is estimated that global waters would rise by 10 cm (4 in).^[