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
Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and s ...
, slope failure, and
hyaloclastite
Hyaloclastite is a volcanoclastic accumulation or breccia consisting of glass (from the Greek ''hyalus'') fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin margin ...
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
The British Antarctic Survey (BAS) is the United Kingdom's national polar research institute. It has a dual purpose, to conduct polar science, enabling better understanding of global issues, and to provide an active presence in the Antarctic o ...
following their survey in 1946.
Environment
Topography
Brown Bluff has a cobble and
ash
Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
beach rising increasingly steeply towards towering red-brown
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
cliffs embedded with
bombs
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanic ...
and
tephra
Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism.
Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they rem ...
. The cliffs are heavily eroded, resulting in loose
scree
Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically ha ...
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
Lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
''
Xanthoria
''Xanthoria'' is a genus of lichenized fungi in the family Teloschistaceae. Common names include orange lichen,Caloplaca'' have been recorded on exposed boulders from the shoreline to an elevation of .
Moss
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
es occur at higher elevations near glacial drainage.
The site has been identified as an
Important Bird Area
An Important Bird and Biodiversity Area (IBA) is an area identified using an internationally agreed set of criteria as being globally important for the conservation of bird populations.
IBA was developed and sites are identified by BirdLife Int ...
(IBA) by
BirdLife International
BirdLife International is a global partnership of non-governmental organizations that strives to conserve birds and their habitats. BirdLife International's priorities include preventing extinction of bird species, identifying and safeguarding ...
because it supports a breeding colony of about 20,000 pairs of
Adélie penguin
The Adélie penguin (''Pygoscelis adeliae'') is a species of penguin common along the entire coast of the Antarctic continent, which is the only place where it is found. It is the most widespread penguin species, and, along with the emperor p ...
s, as well as about 550 pairs of
gentoo penguins
The gentoo penguin ( ) (''Pygoscelis papua'') is a penguin species (or possibly a species complex) in the genus ''Pygoscelis'', most closely related to the Adélie penguin (''P. adeliae'') and the chinstrap penguin (''P. antarcticus''). The ea ...
Wilson's storm petrel
Wilson's storm petrel (''Oceanites oceanicus''), also known as Wilson's petrel, is a small seabird of the austral storm petrel family Oceanitidae. It is one of the most abundant bird species in the world and has a circumpolar distribution mainly ...
s and
kelp gull
The kelp gull (''Larus dominicanus''), also known as the Dominican gull, is a gull that breeds on coasts and islands through much of the Southern Hemisphere. The nominate ''L. d. dominicanus'' is the subspecies found around South America, part ...
s.
Weddell seal
The Weddell seal (''Leptonychotes weddellii'') is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expeditions led by British sealing ...
leopard seal
The leopard seal (''Hydrurga leptonyx''), also referred to as the sea leopard, is the second largest species of seal in the Antarctic (after the southern elephant seal). Its only natural predator is the orca. It feeds on a wide range of prey incl ...
s 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
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 di ...
formed by violent
phreatic eruption
A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evapo ...
s under the lake formed in the ice cap by the magmatic heat. The middle yellow layers are
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 ...
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