Cockburn Island is an oval

island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...

long, consisting of a high plateau with steep slopes surmounted on the northwest side by a

pyramidal peak A pyramidal peak, sometimes called a glacial horn in extreme cases, is an angular, sharply pointed mountain peak which results from the cirque erosion due to multiple glaciers diverging from a central point. Pyramidal peaks are often examples ...

high, lying in the north-east entrance to Admiralty Sound, south of the north-east end of the Antarctic Peninsula. It was discovered by a British expedition (1839–43) led by Captain

James Clark Ross Sir James Clark Ross (15 April 1800 – 3 April 1862) was a British Royal Navy officer and polar explorer known for his explorations of the Arctic, participating in two expeditions led by his uncle John Ross, and four led by William Edwa ...

, who named it for Admiral Sir George Cockburn, then serving as First Naval Lord (commander-in-chief of the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against ...

Geology

Geologically, the area makes up the Cockburn Island Formation, which was studied extensively in the late 1990s by H. A. Jonkers. Rocks found on the island are volcanic, and the island is characterized by its "precipitous cliffs". A "Pecten conglomerate" from the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

period has been identified on the island, situated on a wave-cut platform at 720–820 ft. The island is a rare volcano type called a

tuya A tuya is a flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are rare worldwide, being confined to regions which were covered by glaciers and had active volcanism during the same period. As lava ...

, or moberg, which was formed by a three-stage eruption sequence below an ice cap. The first stage was a subglacial hyaloclastic eruption under a thick ice cap, which shattered the lava into

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

, ash and sand, which has since weathered to yellow

palagonite Palagonite is an alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt. Palagonite can also result from the interaction between water and basalt melt. The water flashes to steam on contact w ...

layers. The second phase was a lava eruption into a meltwater glacial lake contained in the ice cap, which resulted in volcanic

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

and

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discont ...

(boulders of this can be seen along the shore). The final phase was subaerial basalt lava flows on top of the previous volcanic deposits after the lake drained or boiled away.

Wildlife

The island has been identified as an Important Bird Area (IBA) by BirdLife International because it supports a breeding colony of about 800 pairs of

Antarctic shag The Antarctic shag (''Leucocarbo bransfieldensis''), sometimes referred to as the imperial cormorant, king cormorant, imperial shag, blue-eyed shag or Antarctic cormorant, is the only species of the cormorant family found in the Antarctic. It is s ...

s, as well as about 16,000 breeding pairs of Adélie penguins (estimated from 2011 satellite imagery.

Snow petrel The snow petrel (''Pagodroma nivea'') is the only member of the genus ''Pagodroma.'' It is one of only three birds that has been seen at the Geographic South Pole, along with the Antarctic petrel and the south polar skua, which have the most s ...

nests were reported from the island in 1901; it is not known whether they continue to breed there.

Joseph Dalton Hooker Sir Joseph Dalton Hooker (30 June 1817 – 10 December 1911) was a British botanist and explorer in the 19th century. He was a founder of geographical botany and Charles Darwin's closest friend. For twenty years he served as director of ...

, at the time a junior naturalist stationed aboard , made a series of botanical collections on the island in 1843.

References

External links

* {{Important Bird Areas of Antarctica Islands of Trinity Peninsula Important Bird Areas of Antarctica Seabird colonies Penguin colonies Tuyas of Antarctica Volcanic islands

Geology

Wildlife

See also

References

External links