"Summary of volcano hazards at Great Sitkin volcano: 1. Volcanic ash clouds Clouds of fine volcanic ash will drift away from the volcano with the wind, which generally blows from the west. Ash clouds from Great Sitkin Volcano are a hazard to all aircraft downwindfrom the volcano. Airborne volcanic ash can drift thousands of kilometers from its source volcano and typically will remain in the atmosphere for days to months. Ash from future eruptions could interfere with regional air travel, especially during a large, sustained eruption . 2. Volcanic ash fallout Ash fallout from historical and prehistorical eruptions of Great Sitkin Volcano reached all parts of Great Sitkin Island. Fine ash was deposited on the flanks of the volcano during the last eruption in 1974. Heavy ash fall can disrupt many human activities, interfere with power generation, affect visibility, and damage electrical components and equipment. 3. Ballistics During most eruptions, cobble-sized and larger fragments of volcanic rock may be explosively ejected from the vent. These particles are called volcanic bombs or ballistics. Ballistic fallout could occur within a few kilometers of the vent and would be hazardous to people or aircraft near the volcano. 4. Lahar and lahar-runout flows Hot, volcanic debris interacts with snow and ice may generate fast-moving slurries of water, mud, rocks, and sand. […]. 5. Pyroclastic flows and surges Hot, granular material expelled from the volcano may travel rapidly down the volcano flanks as flows of volcanic debris called pyroclastic flows and surges."
Open-File Report 03-112
Alaska Volcano Observatory: http://www.avo.alaska.edu/