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Herðubreið, Iceland

A tuya is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are somewhat rare worldwide, being confined to regions which were formerly covered by continental ice sheets and also had active volcanism during the same time period. Tuyas are a type of subglacial volcano that consists of nearly horizontal beds of basaltic lava capping outward-dipping beds of fragmental volcanic rocks, and they often rise in splendid isolation above a surrounding plateau. Examples of tuyas are found throughout Iceland and also in British Columbia and the Santiam Pass region in Oregon. Tuyas in Iceland are sometimes called table mountains because of their flat tops.

S. Holland, a geographer for the British Columbia government, described tuyas in the following way: "They have a most interesting origin...[they were] formed by volcanic eruptions which had been thawed through the Pleistocene 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."

The Table, British Columbia, Canada

The origin of the term comes from Tuya Butte, one of many tuyas in the area of the Tuya River and Tuya Range in far northern British Columbia. While still in graduate school in 1947, Canadian geologist 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. The 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 the Yukon Territory.

• Mathews, W. H. (1947). "Tuyas, flat-topped volcanoes in northern British Columbia". American Journal of Science 245 (9): 560–570. 
• Mathews, W. H. (1951). "The Table, a flat-topped volcano in southern British Columbia". American Journal of Science 249 (11): 830–841. 
• Landforms of British Columbia: A Physiographic Outline, S. Holland, Govt of BC, 1976, pp 51-52.

• Canadian Mountain Encyclopedia entry on Kawdy Plateau
• Canadian Mountain Encyclopedia entry on Tuya Butte