Davidof Volcano
Encyclopedia
Davidof Volcano is an inactive stratovolcano
and caldera remnant in the Aleutian Islands of Alaska
, USA, 1237 miles (1,991 km) from Anchorage. Located on the eponymous island
, Davidof is part of the Rat Islands
sub-chain. It is also part of the "Aleutian Krakatau", a group of four islands formed when a stratovolcano's caldera caved in during the late Tertiary
.
, albeit that the town is 199 miles (320 km) from the island.
s in the area, about 8% of the world's volcanoes, and most of these are located among the Aleutian Islands. The Aleutian Islands arc forms the northern boundary of the Pacific Ring of Fire
, where tectonic activity generates earthquakes and volcanic eruptions regularly.
The largest of four tiny islands in the "Aleutian Krakatau" caldera, Davidof is a stratovolcano and caldera remnant of a larger stratovolcano, which presumably collapsed at the end of the Tertiary
period. In all, the caldera extends for 262 feet (80 m) underwater. Davidof Island's shape is abstract, with many inclining, steep features and several sea cliffs. There are no visible water features.
Davidof's exact composition is unknown, although studies conducted by W.H. Nelson of the United States Geological Survey
(USGS) determined that the lava, at least, was layered over a base of red breccia
. The lavas appeared to be differentiating, but stuck to gray color with either "glassy or fine-grained, compact or dikty-taxitic" composition. Much like Segula Island
, all of Davidof's lava and even pyroclastic deposits interact by overlapping with each other. The uppermost layer of these deposits is formed by the pyroclastic flow deposits.
The lava is filled with phenocrysts like feldspar
, olivine
, and pyroxene
, and these can be found easily about the lava areas.
, and heath
. Spread throughout the island are grass and sedge
s, which cover much of the lower surface. Fungi, liverwort
s, horsetail
s, and fern
s, can be found on the island, along with flowering plant
s, such as the narcissus anemone
, lupin
es, and orchids. Seaweed is also common on the island's beaches.
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
and caldera remnant in the Aleutian Islands of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, USA, 1237 miles (1,991 km) from Anchorage. Located on the eponymous island
Davidof Island
Davidof Island is an island in the Rat Islands archipelago of the Western Aleutian Islands, Alaska. Davidof Island is irregular in shape with a north-south length of 2 miles and a greatest width of 0.7 mile. The high point in the south part is 1,074 feet, and the summit in the north part is 922...
, Davidof is part of the Rat Islands
Rat Islands
The Rat Islands are a volcanic group of islands in the Aleutian Islands in southwest Alaska, between Buldir Island and the Near Islands group to its west, and Amchitka Pass and the Andreanof Islands group to its east, at about ....
sub-chain. It is also part of the "Aleutian Krakatau", a group of four islands formed when a stratovolcano's caldera caved in during the late Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
.
Accessibility
Since the island is uninhabited, very little transportation is available. Transport can be found in AdakAdak, Alaska
Adak , formerly Adak Station, is a city in the Aleutians West Census Area, Alaska, United States. At the 2010 census the population was 326. It is the westernmost municipality in the United States and the southernmost city in Alaska. The city is the former location of the Adak Army Base and Adak...
, albeit that the town is 199 miles (320 km) from the island.
Geography and geology
Because of the inclusion of Alaska, the United States has the largest number of active volcanoes in the world, many of them geologically young. In Alaska, at least 50 volcanoes, including those in the Aleutian archipelago, have erupted in historical time. Alaska accounts for about 80% of the United States' volcanoes, excluding the seamountSeamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s in the area, about 8% of the world's volcanoes, and most of these are located among the Aleutian Islands. The Aleutian Islands arc forms the northern boundary of the Pacific Ring of Fire
Pacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
, where tectonic activity generates earthquakes and volcanic eruptions regularly.
The largest of four tiny islands in the "Aleutian Krakatau" caldera, Davidof is a stratovolcano and caldera remnant of a larger stratovolcano, which presumably collapsed at the end of the Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
period. In all, the caldera extends for 262 feet (80 m) underwater. Davidof Island's shape is abstract, with many inclining, steep features and several sea cliffs. There are no visible water features.
Davidof's exact composition is unknown, although studies conducted by W.H. Nelson of the United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
(USGS) determined that the lava, at least, was layered over a base of red breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
. The lavas appeared to be differentiating, but stuck to gray color with either "glassy or fine-grained, compact or dikty-taxitic" composition. Much like Segula Island
Segula Island
Segula Island is an island in the Rat Islands archipelago of the western Aleutian Islands, Alaska. It consists of a Holocene stratovolcano, called Segula Volcano.Segula Island is three to four miles in diameter, and is located about east of Kiska Island...
, all of Davidof's lava and even pyroclastic deposits interact by overlapping with each other. The uppermost layer of these deposits is formed by the pyroclastic flow deposits.
The lava is filled with phenocrysts like feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
, olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
, and pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
, and these can be found easily about the lava areas.
Eruptive history
Although no eruptions have been recorded at Davidof, there is evidence of activity at the volcano. Through aerial photography, lava flow deposits have been detected among the flanks of the island.Wildlife
Despite its small size, Davidof is heavily vegetated, with variations of moss, lichenLichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
, and heath
Heath (habitat)
A heath or heathland is a dwarf-shrub habitat found on mainly low quality acidic soils, characterised by open, low growing woody vegetation, often dominated by plants of the Ericaceae. There are some clear differences between heath and moorland...
. Spread throughout the island are grass and sedge
Sedge
- Plants :* Acorus calamus, sweet flag, a plant in the Acoraceae family* Any of the plants in the family Cyperaceae- Animals :* A collective noun for several species of birds, including bitterns, cranes and herons* Sedge-fly, caddisfly- Other uses :...
s, which cover much of the lower surface. Fungi, liverwort
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
s, horsetail
Horsetail
Equisetum is the only living genus in the Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.Equisetum is a "living fossil", as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and...
s, and fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, can be found on the island, along with flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s, such as the narcissus anemone
Anemone narcissiflora
Anemone narcissiflora is a herbaceous perennial in the genus Anemone and the buttercup family.-Description:...
, lupin
Lupin
Lupinus, commonly known as Lupins or lupines , is a genus in the legume family . The genus comprises about 280 species , with major centers of diversity in South and western North America , and the Andes and secondary centers in the Mediterranean region and Africa Lupinus, commonly known as Lupins...
es, and orchids. Seaweed is also common on the island's beaches.