MT. SPURR
Several Aleutian Arc volcanoes periodically threaten
cities and towns in the Anchorage area of southern Alaska, USA. The
Aleutian Volcanic Arc consists of dozens of volcanoes, all formed by subduction
of the Pacific Plate beneath the North American Plate. Mt. Spurr, in the northeastern Aleutian
Volcanic Arc, is a 10-20,000 year old andesitic, subduction zone stratovolcano that
formed after the collapse of a Late Pleistocene volcano (“ancestral Spurr
Volcano”). Spurr Volcano had ash
eruptions in 1953 and 1992.
Porphyritic andesite volcanic ash - from 5 AM to 6 AM on 9 July 1953, Mt. Spurr had an
explosive ash eruption from the Crater Peak Vent, a satellite eruptive
center. Crater Peak Vent is a
basaltic-andesitic cone located just south of Mt. Spurr's summit.
The 1953 ash cloud reached 70,000’ high and blanketed
the city of Anchorage with an approximately quarter-inch thick (~0.25”) layer
of ash, which fell from about noon to late afternoon on 9 July 1953.
Hornblende andesite volcanic ash (field of view ~5.1 cm across) - on 18 August 1992,
Mt. Spurr, had a 3.5-hour long, subplinian ash eruption. Ash coated the
city of Anchorage. Like the 1953 eruption, the 1992 eruption was also
from the Crater Peak Vent.
For additional information on the 1953 and 1992
eruptions, see:
Wilcox (1953) - Preliminary
Report of the Eruption of Mount Spurr Volcano, Alaska, July 9, 1953, and the
Ashfall in the Anchorage Area. 25
pp.
Keith (1995) - The 1992 eruptions of Crater Peak Vent,
Mount Spurr Volcano, Alaska. U.S. Geological Survey Bulletin
2139. 223 pp.