Shishaldin Volcano

Shishaldin Volcano, or Mount Shishaldin (), is a moderately active volcano on Unimak Island in the Aleutian Islands chain of Alaska in the United States. It is the highest mountain peak of the Aleutian Islands and rises about 10,000 m (33,000 ft) from the bottom of the Aleutian Trench 140 mi (230 km) south of the volcano. The volcano's topographic contour lines are nearly perfect circles above 6,500 ft (2,000 m). The lower north and south slopes are somewhat steeper than the lower eastern and western slopes. Only on the volcano's west flank between about 3,500 to 6,500 ft (1,100 to 2,000 m) are small areas of rough topography which are remnants of an older collapsed volcano upon which Shishaldin is built. The volcano is the westernmost of three large stratovolcanoes along an east–west line in the eastern half of Unimak Island.

The upper 6,600 ft (2,000 m) is almost entirely covered by glacial snow and ice. In all, Shishaldin's glacial shield covers about 35 sq mi (91 km2). 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 4,900 to 5,900 ft (1,500 to 1,800 m) elevation. The Shishaldin edifice contains about 300 km3 (72 cu mi) of material. A very steady steam plume rises from its small summit crater which is about 500 ft (150 m) across and slightly breached along the north rim. In appearance, the volcano can vary from nearly completely white to almost all black, depending on the occurrence of ashfall deposits.

In 1967, Shishaldin Volcano was designated as a National Natural Landmark - the Shishaldin Volcano National Natural Landmark - by the National Park Service. The landmark is 62,714 acres (25,379 ha) and a plaque was erected near the coast.