Frequently Asked Questions
How many active volcanoes are there in Alaska?
The Catalog of Historically Active Volcanoes of Alaska lists 41 historically active volcanoes. There are 127 identified volcanic features in Alaska that are known or presumed to have been active within the last 2 million years. There are at least a few more on land, and perhaps many more below sea level, which have not been described yet. Those that are not "active" are "dormant", or perhaps "extinct."
The definition of what is an active volcano is complicated and varies from place to place depending on the time of recorded history in a region. This can be further complicated by different interpretations of what constitutes an eruption – for example, steam explosions can indicate unrest at a volcano, but do not constitute an eruption because no new magma has come to the surface.
Why are there volcanoes in Alaska?
Most volcanic activity in Alaska is the result of one tectonic plate diving beneath another in a process called ‘subduction’. In the Aleutian Arc, the northward-moving Pacific Plate slides under the southern edge of the North American Plate at a rate of 6 to 7.5 centimeters (2.5 to 3 inches) per year. The release of water from hydrous minerals as they are pressurized deep within this subduction zone lowers the melting point of the overriding plate to form buoyant magmas that rise to the surface to form volcanoes.
If nobody lives up there, what hazards are there from eruptions at Alaskan volcanoes?
The airspace over Alaska is extremely busy with long-range, wide-body aircraft as well as bush planes and smaller aircraft. The Anchorage International Airport handles more international air freight (in dollar value) than any other airport in the United States. Thousands of aircraft and people fly over or near Alaska volcanoes every day. A considerable percent of all air freight on earth passes near Alaska's many volcanoes.
If an aircraft encounters volcanic ash it can cause severe damage to the engines as well as other parts of the airplane. Two processes damage jet engines, particularly long-range, wide-body airplanes such as DC-10s and Boeing 747s that are used for international transport. Mechanical abrasion can damage the moving parts in a jet engine, such as the compressor and turbine blades. Ingestion of hot ash can clog fuel nozzles, combustor, and turbine parts causing surging, flame out, immediate loss of engine thrust, and engine failure.
How often do volcanoes in Alaska erupt?
At least 265 historical eruptions have occurred at 29 Alaskan volcanoes (and possibly 45 others) since 1760 giving a frequency rate of 1.1 - 1.3 eruptions per year. It is possible that many eruptions in the early part of Alaska’s history went unreported, so this is a minimum estimate. Over the 50-year period 1945 (the end of World War II) through 1994, 90 eruptions were reported from 23 volcanoes for a frequency of about 2 (1.8) eruptions per year. These are estimates of the number of separate eruptions per year, but many individual eruptive episodes occur over weeks or months. In any one year it is not unusual for 3 or 4 of Alaska’s volcanoes be active.
