Mt. Spurr Kylie Walters and Danielle Gould Dept. of Geology, Colby College

Geographic and Volcanic Setting ●Northeastern end of Aleutian volcanic arc ●Zone where denser Pacific oceanic plate subducts under North American plate ●Pacific Ring of Fire

Volcanic Form and Dimensions ●Stratovolcano grown in center of caldera ~12 miles (19 km) around ●Highest volcano in the Aleutian Arc (3,374 m summit, 11,067 ft elevation) ●Mostly two-pyroxene andesite composition ●Base covered by thick ash flows, pyroclastic deposits

Mt. Spurr’s Caldera ★ Inferred Caldera -5-6 km wide -controversy → coincidental or formation from Bezymianny- type eruption at the end of the last ice age? -dome houses new Mt. Spurr

Vents and Craters ●Crater Peak Vent -3.2 miles south on Caldera rim -small stratocone -summit crater (w/lake)

Eruptive History ●Ash eruption on July 9, 1953 from Crater Peak on South Flank ●Crater Peak erupted again three times in 1992 following 10 months of heightened seismicity (June 27, August 18 & Sept. 16) ●VEIs of 4 ●Became forming ~255,000 yrs ago ●5 prior eruptions dated by scientists

Eruptive Style ●Sub-Plinian -Explosive -Pyroclastic flows -Lava Bombs -Lahars -Viscous andesitic lava flows -Debris avalanches -Ash <5mm→ closed airports, damaged equipment, economic losses

Volcanic Hazards ●Eruption column from August 18, 1992 (~13.5 km) ●Disruption to U.S. air travel ●Ashfall on Anchorage - $2 million in damage ●Melting snow and ice ●Ash trouble in dry season ●Lava bombs can travel more than 30 Km

Volcanic Deposits ●Pre-1953 → Caldera’s collapse led to avalanche deposits ●~6 mm of Andesitic ash fell on Anchorage ~125 km to the East ●Large lahars (100,000 m 3 ) due to glaciers-blocked the Chakachatna River (in 1992 as well)

Volcanic Deposits ★ June 27-Ash went 9 Km high and 200 Km wide SO Km ★ August 18-Ash went 13.5 Km high and 600 Km away at Beaver Creek; 5 mm thick ★ Lava bombs-8mm to 2 m large fell 2-4 Km from Crater Peak, some, 8 Km ★ September ,000 tons of SO 2 and 12,000 tons of CO 2

Petrology ●Major: Andesite, Basaltic Andesite ●Minor: Dacite, Basalt/Picro-Basalt, Rhyolite -SiO 2 = 57% -plagioclase, pyroxene, hornblende -very little glass ●Small pieces of metamorphic rock ●From pyroclastic flows

Hydrothermal Activity and Tourism ●Fumaroles-steam vents near volcano base ●Alaska Flightseeing Tour of the Triumvirate Glacier and Mt. Spurr ●Not a major site for tourists ○ Hiking April through October

Active Monitoring ●Alaska Volcano Observatory (AVO) ●8 seismographs -1 on crater rim before 1992 eruption -monitored for past 33 years ~10 earthquakes per month! ●Gas levels are monitored

Works Cited AVO Web Team, 2014: Mount Spurr Description and Information, at (accessed 24 January, 2015) Crossen, Kristine J., 2001: Aleutian Volcanoes and Plate Tectonics on the Pacific Rim, at (accessed 25 January, 2015) March, Rod, 2010: Snow and Ice on Volcanoes in Alaska, at (accessed 25 January, 2015) McGimsey, Robert G., Neal, Christina A., Riley, Colleen M., 2001: Areal Distribution, Thickness, Mass, Volume, and Grain Size of Tephra-Fall Deposits from the 1992 Eruptions of Crater Peak Vent, Mt. Spurr Volcano, Alaska: U.S. Geological Survey Open-File Report , at (accessed 23 January, 2015) Mount Spurr Mountain Information, 2015: Mount Spurr – Climbing, Hiking & Mountaineering, at (accessed 23 January, 2015) Regal Air, 2010: Triumvirate Glacier and Mt. Spurr Volcano Flightseeing Tour, at (accessed 25 January, 2015) Smithsonian Institution, 2013: Spurr, at (accessed 25 January, 2015) The Regents of the University of California, 2015: The Holocene Epoch, at (accessed 24 January, 2015)

Works Cited (cont.) Waythomas, Christopher F., and Christopher J. Nye. Preliminary Volcano-Hazard Assessment for Mount Spurr Volcano, Alaska. Publication no Anchorage: US Geological Survey, Print. Wood, Charles A. and Kienle, Jurgen, "Volcanoes of North America United States and Canada," Cambridge University Press, New York, 354 pp., USGS. Alaska Volcano Observatory Images Assorted images from USGS sites.