A tuya is a flat-topped, steep-sided
volcano
A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most oft ...
formed when
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
erupts through a thick
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
or
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
. They are rare worldwide, being confined to regions which were covered by
glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
s and had active volcanism during the same period.
As lava that erupts under a glacier cools very quickly and cannot travel far, it piles up into a steep-sided hill. If the eruption continues long enough, it either melts all the ice or emerges through the top of the ice and then creates normal-looking lava flows that make a flat cap on top of the hill. Discovering and dating the lava flows in a tuya has proven useful in reconstructing past glacial ice extents and thicknesses.
Formation
Tuyas are a type of
subglacial volcano that consists of nearly horizontal beds of
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
capping outward-dipping beds of fragmental volcanic rocks, and they often rise in isolation above a surrounding
plateau
In geology and physical geography, a plateau (; ; : plateaus or plateaux), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. ...
. Tuyas are found in
Iceland
Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...
,
British Columbia
British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, the
Santiam Pass region in
Oregon
Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
, the
Tyva Republic in eastern Russia,
the
Antarctic Peninsula
The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martin in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctica.
...
and beneath the
West Antarctic Ice Sheet
The West Antarctic Ice Sheet (WAIS) is the segment of the Antarctic ice sheet, continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. It is cla ...
. Tuyas in Iceland are sometimes called ''table mountains'' because of their flat tops.
S. Holland, a
geographer
A geographer is a physical scientist, social scientist or humanist whose area of study is geography, the study of Earth's natural environment and human society, including how society and nature interacts. The Greek prefix "geo" means "earth" a ...
for the British Columbia government, described tuyas in the following way:
:"They have a most interesting origin ...
hey wereformed by volcanic eruptions which had been thawed through the
Pleistocene
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
ice-sheet by underlying
volcanic heat. The lavas capping the mountains were extruded after the volcanoes were built above lake-level, and the outward-dipping beds were formed by the chilling of the lava when it reached the water's edge."
Because they erupt under ice and water, tuyas have
phreatomagmatic eruptions creating layers of
breccia 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 marg ...
above
pillow lavas. If the volcano breaches the surface of the glacier it will be topped by a
subaerially erupted
lava plateau.
Etymology
The origin of the term comes from
Tuya Butte
Tuya Butte is a tuya in the Tuya Range of north-central British Columbia, Canada. It is a bit less isolated from other ranges than neighbouring Mount Josephine (British Columbia), Mount Josephine. Some of the other volcanoes in the area include ...
, one of many tuyas in the area of the
Tuya River
The Tuya River is a major tributary of the Stikine River in northwest part of the province of British Columbia, Canada. From its source at High Tuya Lake in Tuya Mountains Provincial Park just south of Ash Mountain, the highest peak of the Tuy ...
and
Tuya Range in far northern
British Columbia
British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
,
Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
.
While still in graduate school in 1947, Canadian
geologist
A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...
Bill Mathews published a paper titled, "Tuyas, Flat-Topped Volcanoes in Northern British Columbia", in which he coined the term "tuya" to refer to these distinctive volcanic formations. Tuya Butte is a near-ideal specimen of the type, the first such landform analyzed in the geological literature, and this name has since become standard worldwide among volcanologists in referring to and writing about these formations.
Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of
Tuya Lake and south of the
Jennings River near the boundary with
Yukon
Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...
. Around the same time that Mathews published his paper, the Icelandic geologist Guðmundur Kjartansson had distinguished between "móberg" ridges and tuyas in Iceland and proposed the hypothesis that they were formed during subglacial and intraglacial eruptions.
The term ''tuya'' may be derived from a
Tahltan word.
BCGNIS Query Results
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Examples
See also
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References
Further reading
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External links
Canadian Mountain Encyclopedia entry on Kawdy Plateau
Canadian Mountain Encyclopedia entry on Tuya Butte
{{Commons category, Tuyas
Volcanoes