Tuya
U.S. Geological Survey photo by Mary Chapman (fair use policy)
This tuya, named Hjorleifshofdi, sits on the Myrdalssandur outwash plain or sandur, in Iceland. A tuya is a table mountain that forms when a small volcano erupts underneath a glacier. At first, the lava erupts in much the same way it does in the deep sea, forming a pile of lava pillows. Part of the lava shatters as it contacts the ice, leaving a kind of glassy breccia called hyaloclastite.
After a while the ice above the eruption melts into a lake, and the more explosive interactions of fire and shallow water yield mainly hyaloclastite. When the lake is filled or boiled away, lava flows more gently again, forming thick flows, often with columnar jointing that forms as the rock slowly cools. All of these stages are visible in Hjorleifshofdi.
The name tuya comes not from Icelandic, but from the Tuya region of British Columbia where many subglacial volcanic features have been described.
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