Volcano-Glacier Interactions during Recent Volcanic Unrest at Aleutian Arc Volcanoes [*C.F. Waythomas*] (USGS, Alaska Volcano Observatory, 4230 University Drive, Suite 201, Anchorage, AK, USA, 99508; ph: 907-786-7122; fax: 907-786-7150; email: chris@usgs.gov); C.A. Neal (USGS, Alaska Volcano Observatory, 4200 University Drive, Anchorage, AK, USA, 99508; ph: 907-786-7458; fax: 907-786-7425; email: tneal@usgs.gov); R.G. McGimsey (USGS, Alaska Volcano Observatory, 4200 University Drive, Anchorage, AK, USA, 99508; ph: 907-786-7432; fax: 907-786-7150; email: mcgimsey@usgs.gov); K. Bull (Alaska DGGS, Alaska Volcano Observatory, 3354 College Rd., Fairbanks, AK, USA, 99709; ph: 907-451-5055; fax: 907-455-6879; email: kate_bull@dnr.state.ak.us); R. Wessels (USGS, Alaska Volcano Observatory, 4200 University Drive, Anchorage, AK, USA, 99508; ph: 907-786-7492; fax: 907-7867425; email: rwessels@usgs.gov); M.L. Coombs (USGS, Alaska Volcano Observatory, 4200 University Drive, Anchorage, AK, USA, 99508; ph: 907-786-7403; fax: 907-7867425; email: mcoombs@usgs.gov, K.L. Wallace (USGS, Alaska Volcano Observatory, 4230 University Drive, Suite 201, Anchorage, AK, USA, 99508; ph: 907-786-7109; fax: 907-786-7150; email: kwallace@usgs.gov); C. Huggel (Department of Geography, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland; ph: +41 44 635 51 75; fax: +41 44 635 68 41; email:chuggel@geo.unizh.ch Recent unrest at Aleutian arc volcanoes has provided a number of diverse examples of the interaction between volcanic processes and glaciers, ice and snow. The case studies described below, illustrate how these interactions may lead to potentially hazardous outcomes and how knowledge of these phenomena may help mitigate hazards posed by volcano-glacier interactions elsewhere. The 1989-90 eruption of Redoubt volcano (60.485 N, 152. 744 W) was an explosive dome-building eruption that physically removed the upper one third of Drift Glacier, a 14 km2 valley glacier on the northeast flank of the volcano. Pyroclastic flows and surges ravaged the lower reaches of Drift Glacier and led to lahars and floods that inundated the Drift River valley, including an oil storage and transfer facility near the mouth of the Drift River about 40 km downstream of the volcano. This eruption highlights pyroclastic flow interaction with ice and snow and the subsequent generation of destructive lahars. The 1983-84 eruption of Veniaminof volcano (56.195 N, 159.39 W) was a Strombolian eruption from a vent within the 8-km-diameter ice-filled caldera that characterizes the volcano. Lava flows produced during the eruption created ice cauldrons that evolved to open melt pits with ephemeral lakes. Although catastrophic release of water and flooding did not occur, larger eruptions that produce more extensive lava flows could lead to outburst floods from the caldera ice field. This eruption highlights lava-flow interaction with glacier ice. Augustine Volcano (59.363 N, 153.435 W) erupted explosively in January- February 2006. Pyroclastic flows generated during the explosive phase of the eruption swept across steep, extensively snow-covered slopes on all flanks of the volcano. The snow blanket caused the flows to inflate, spread out, and form thin, sheet-like pyroclastic-flow deposits. Pyroclastic flows erupted later, that did not interact with snow, followed drainages and produced deposits with more classic morphology, including blocky, lobate margins and levees. Lahars and mixed avalanches of snow, water, and pyroclastic debris formed beyond the pyroclastic flows that swept across snow. Flow morphologies, lithologies, and depositional contacts indicate that the lahars and mixed avalanches evolved from these pyroclastic flows. These deposits highlight the interaction between snow and pyroclastic debris. Volcanic unrest at Mt. Spurr volcano (61.298 N, 152.253 W) from 2004 to present has resulted in the development of a 200 x 200 m diameter, lake bearing melt pit at the 3374 m high summit of the volcano, and several episodes of unusual water release. Although no eruption of the Mt. Spurr summit vent has occurred, the melt pit lake remains open and partially ice free. This unrest highlights low-level geothermal interaction with ice and snow. On September 17, 2006, a major steam emission occurred at Fourpeaked volcano (58.769 N, 153.674 W) that produced a plume reaching about 6000 m above sea level. Observations made after the event indicated that a small debris flow and several melt pits developed on the north flank of the volcano. The debris flow was the product of an outburst event that may have initiated the collapse of an ice vault above the newly reinvigorated hydrothermal vent system. The collapsing ice vault is thought to have brought glacier ice and water into rapid contact with hot gasses and rock leading to a phreatic eruption that produced the steam plume observed on September 17, 2006. This unrest highlights explosive water-ice-hydrothermal interaction. These examples are representative of the diverse range of volcano-glacier interactions in Alaska during recent periods of unrest. The high frequency and range of interactions offers many possibilities for further study and illustrates the importance of this region as a natural laboratory for study of volcano-ice interactions. ABSTRACT SUBMITTED FOR POSTER SESSION CORRESPONDING AUTHOR: Chris Waythomas, USGS, Alaska Volcano Observatory, 4230 University Drive, Suite 201, Anchorage, AK, 99508, chris@usgs.gov