Gunung es A-38

A-38 adalah gunung es besar yang terpisah dari Paparan es Filchner-Ronne di Antarctica pada Oktober 1998. Segera setelah pembentukan, gunung es terpisah menjadi dua bagian, A-38A dan A-38B, yang mengambang ke barat di Pusaran Weddell. Gunung-gunung es bergerak ke utara sepanjang Semenanjung Antarktika dan mencapai ujung pada Februari 2003. Gunung es A-38A dan A-38B meningkatkan kecepatan di laut terbuka dan mendarat di perairan dangkal di timur Pulau Georgia Selatan pada December 2003. A-38A pecah menjadi tiga bagian pada Maret 2004 dan mengambang ke utara tempat gunung itu kemudian musnah. A-38B berpecah menjadi dua pada bulan April, dengan bagian timur, kini dikenal dengan A-38G, mengambang ke utara dan barat hingga musnah. Bagian A-38B yang tersisa tetap berdiam di tempat, sehingga mengganggu jalur mencari makan anjing laut dan penguin di Georgia Selatan serta mengakibatkan kematian anak-anak anjing laut dan penguin. Pada 20 Agustus, A-38B pecah menjadi dua, dengan bagian baru mengambang ke utara dan pecah. Bagian A-38B yang tersisa terus pecah hingga September 2004 dan benar-benar rusak pada 2005.

Runtuhan es

Iceberg A-38 dan Pulau Berkner pada 13 Oktober

Gunung es A-38 runtuh dari Paparan es Filchner-Ronne, Antarktika, pada Oktober 1998 dari posisi dekat Pulau Berkner. Proses runtuhan ini disebabkan karena tekanan yang dibebankan pada paparan es oleh Tonjolan es Hemmen. Runtuhan itu terjadi selama beberapa dasawarsa lewat ceruk dalam paparan es yang diisi dengan es laut, salju, dan gunung es kecil, yang bertambah besar secara bertahap. Dua dari ceruk itu, yaitu ceruk tegak lurus dengan bagian depan paparan es dan ceruk yang sejajar dengannya, bertemu dan mengarah kepada pembentukan A-38. Semasa keruntuhan menjadi A-38, gunung es ini berukuran 150 kilometer kali 50 kilometer. Gunung es ini pertama kali diakui pada 13 Oktober 1998 oleh ilmuwan Pusat Es Nasional Amerika Serikat Mary Keller dari citra yang disediakan lewat Defense Meteorological Satellite Program, meskipun Glenn Grant dan Jeff Otten dari Stasiun Palmer Program Antarktika Amerika Serikat mengklaim telah melihat gunung es pada hari yang sama.

Dengan ukuran 7.100 km², A-38 adalah gunung es terbesar yang diamati dalam satu dasawarsa, melampaui rekor sebelumnya oleh B-9 observed in October 1987. Keruntuhan itu dianggap National Oceanic and Atmospheric Administration sebagai "a possible indicator of global warming". By 16 October it had moved a couple of miles away from the parent ice mass.

Pemisahan dan pergerakan ke utara

Calving location

A-38A

A-38B

A-38C

A-38D

South Georgia

Positions of A-38 fragments in March 2003

By 22 October 1998, A-38 began to split. The iceberg split into two pieces of about equal size that were named A-38A and A-38B, with A-38A being the eastern portion of the original iceberg and A-38B the western portion.

Both portions drifted in the Weddell Gyre westwards towards the Antarctic Peninsula before moving north. The speed of the icebergs varied according to the quantity and thickness of surrounding sea ice, moving much slower in winter than in summer. The icebergs reached the tip of the Antarctic Peninsula in February 2003 and continued to progress northwards away from the continent. Their progress was tracked by the Moderate Resolution Imaging Spectroradiometer satellite. Although both icebergs calved at their edges, their overall shape was largely unaffected.

By March 2003 the iceberg had split into four pieces and were reported at the following locations:

• A-38A at 61°42′S 52°24′W measuring 22 mil (35 km) by 48 mil (77 km)
• A-38B at 63°00′S 51°54′W measuring 22 mil (35 km) by 25 mil (40 km)
• A-38C at 60°30′S 49°48′W measuring 7 mil (11 km) by 11 mil (18 km)
• A-38D at 63°42′S 52°36′W measuring 2 mil (3,2 km) by 10 mil (16 km)

South Georgia

The splitting of A-38B in April 2004

A-38A and A-38B increased speed during their drift in open sea and both icebergs approached South Georgia Island, some 1.500 mil laut (2.800 km) north of their initial position, in December 2003. Both icebergs grounded in shallow seas some distance to the east of the island. On 15 March 2004, A-38A broke into three pieces and began to drift northwards once more. After a few weeks their progress could no longer be monitored by medium-resolution satellite imagery. In January 2004, another fragment of A-38, A-38D, which was covered in meltwater ponds, had drifted past South Georgia.

A-38B remained grounded 100 kilometer (62 mi) off South Georgia and on 12 April 2004 was measured at 25 mil laut (46 km) in length. It had broken into two portions, almost equal in size, by 15 April 2004. The western portion remained known as A-38B while the eastern portion was named A-38G. From 17 to 18 April, A-38G drifted north and then west, decaying below satellite imagery detection capability within a few weeks. Iceberg A-38B remained grounded for some months, affecting the foraging routes of adult seals and penguins, resulting in the death of young penguins and seals on the beaches of South Georgia. A-38B broke into two along an existing crackline on 20 August 2004. The new iceberg fragment drifted northwards and broke up. A-38B continued to break up through August and September 2004 and had disappeared by 2005.

Documentation

A-38 offered researchers an opportunity to observe the breaking up and decay of an iceberg, though the imagery was affected by heavy cloud cover in the region around South Georgia. Because the iceberg was grounded (and therefore stationary) high-resolution imagery from the Advanced Spaceborne Thermal Emission and Reflection Radiometer satellite could be ordered to investigate it. This allowed researchers to test models of melting and decay against a real-life example.

Lihat pula

• Iceberg A-68