A tuya is a flat-topped, steep-sided volcano that was formed when a volcano erupted beneath a glacier or ice sheet. They are named after the Tuya region of British Columbia, where a number of these formations can be found. The best examples of tuyas can be found in Canada and Iceland. They are also called 'subglacial volcanoes' or sometimes 'table mountains', although this term is also used for other formations.

When the volcano first erupts, the lava forms large oozy (or billowy?) looking lumps called pillow lava. (Pillow lava is formed by underwater volcanoes too). Once the volcano has formed a lake around itself and is pushing lava into shallow water, it covers the pillow lava with hyaloclastite, a mish-mash of volcanic materials with lots of tiny obsidian fragments, formed in the churning chaos of cold water and hot lava. Once the water is boiled away, or the volcano builds up above water level, lava can flow more calmly, forming think sturdy lava flows, although jointing may occur, where the lava shrinks as it cools, cracking into tall columns. (Confusingly, these above-water lava flows are called "subaerial lava flows" -- just as subaqueous is below, but still in the water, subaerial is below, but still in the atmosphere).

Tuyas can be useful to geologists because the changes in the lava forms indicate the depth of the ice at the time the volcano erupted. Most well-formed tuyas were formed during the Pleistocene, the latest period of recurring glaciations (the ice age!).

Tuyas are related to guyots ('sea mounts'), underwater volcanoes.


References:
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1262.pdf
http://en.wikipedia.org/wiki/Tuya
http://geology.about.com/library/bl/images/bltuya.htm


Tuya is also the singular possessive pronoun for use with feminine nouns in Spanish; akin to thy and thine in English, although these days we just say yours. It is often used after a noun, so a better English translation might be 'of yours'. ("Esta gata tuya" = "This cat of yours"). The form used with masculine nouns is tuyo.

Thanks to Excalibre for helping me with the mysteries of Spanish grammar.


References:
http://babelfish.altavista.com/tr
spanish/english english/spanish dictionary (sic.) pub. Signet, New American Library, 1969.

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