Global Volcanism Program | Image GVP-09002
The prominent caldera in the center of the photo is Nemrut Dagi, the westernmost of a group of volcanoes near Lake Van. Nemrut Dagi lies north of the western part of Lake Van and is the only one of the group that has erupted in historical time. The 5 x 9 km caldera is partially filled by a lake, which appears as the smooth snow-covered right side of the caldera floor in this Space Shuttle photo with north to the bottom. Ash layers in Lake Van document numerous Holocene eruptions, the last of which took place in 1441 CE.
NASA Space Shuttle image STS45-80-08, 1992 (http://eol.jsc.nasa.gov/).