is a moderately active volcano
on Unimak Island
in the Aleutian Islands
chain of Alaska
. It is the highest mountain peak of the Aleutian Islands. The most symmetrical cone-shaped glacier-clad large mountain on earth, the volcano's topographic contour lines are nearly perfect circles above . The lower north and south slopes are somewhat steeper than the lower eastern and western slopes. The volcano is the westernmost of three large stratovolcanoes
along an east–west line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." The upper 2,000 meters is almost entirely covered by glacial snow and ice. In all, Shishaldin's glacial shield covers about 35 sqmi. It is flanked to the northwest by 24 monogenetic parasitic cones, an area blanketed by massive lava flows. The Shishaldin cone is less than 10,000 years old and is constructed on a glacially eroded remnant of an ancestral somma
and shield. Remnants of the older ancestral volcano are exposed on the west and northeast sides at 1,500–1,800 meters elevation. The Shishaldin edifice contains about 300 cubic kilometers of material. A very steady steam plume rises from its small summit crater which is about across and slightly breached along the north rim.