Brown Bluff is a
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 ...
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 ...
on the
Tabarin Peninsula
Tabarin Peninsula () is a peninsula 15 nautical miles (28 km) long and 5 to 12 nautical miles (22 km) wide, lying south of the trough between Hope Bay and Duse Bay and forming the east extremity of Trinity Peninsula in the Antarctic Pe ...
of northern
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 cont ...
. It formed in the last 1 million years as a result of
subglacial eruptions within an englacial lake. The volcano's original diameter is thought to have been about and was probably formed by a single vent. Brown Bluff is divided into four stages:
pillow
A pillow is a support of the body at rest for comfort, therapy, or decoration. Pillows are used in different variations by many species, including humans. Some types of pillows include throw pillows, body pillows, decorative pillows, and man ...
volcano, tuff cone, slope failure, and hyaloclastite delta; and into five structural units.
The volcano gets its name from its steep slopes and brown-to-black hyaloclastite. It was applied by the Falklands Islands Dependencies Survey following their survey in 1946.
Environment
Topography
Brown Bluff has a cobble and volcanic ash, ash beach rising increasingly steeply towards towering red-brown tuff cliffs embedded with volcanic bomb, bombs and tephra. The cliffs are heavily eroded, resulting in loose scree and rock falls on higher slopes, and large, wind-eroded boulders on the beach. Permanent ice and tidewater glaciers surround the site to the north and south, occasionally filling the beach with brash ice.
Flora and fauna
Lichens in the genus, genera ''Xanthoria'' and ''Caloplaca'' have been recorded on exposed boulders from the shoreline to an elevation of . Mosses occur at higher elevations near glacial drainage.
The site has been identified as an Important Bird Area (IBA) by BirdLife International because it supports a bird colony, breeding colony of about 20,000 pairs of Adélie penguins, as well as about 550 pairs of gentoo penguins. Other birds nesting there include cape petrels, Wilson's storm petrels and kelp gulls.
Weddell seals regularly hauling-out, haul out, and leopard seals often hunt offshore.
Geology
Brown Bluff is a cliff of volcanic rocks consisting of a tuya or moberg, which is a volcano erupted under an icecap. The base layer is breccia formed by violent phreatic eruptions under the lake formed in the ice cap by the magmatic heat. The middle yellow layers are palagonite weathering of steeply dipping ash layers. The top caprock is composed of black layers are basalt flows that erupted after the meltwater lake drained away, resulting in subaerial lava flows.
[Joseph Holliday, Earth Science Department, El Camino College]
References
External links
Secretariat of the Antarctic Treaty Visitor Guidelines and site description*
{{Important Bird Areas of Antarctica
Tuyas of Antarctica
Volcanoes of Graham Land
Landforms of Trinity Peninsula
Important Bird Areas of Antarctica
Seabird colonies
Pleistocene volcanoes
Penguin colonies