An active volcano is one that’s currently in a state of regular eruptions. Maybe it’s going off right now, or had an event in the last few decades. And geologists expect it to erupt again very soon. A dormant volcano is one that is capable of erupting, and will probably erupt again in the future, but it hasn’t had an eruption for a very long time.
And here’s the problem. The lifespan of a volcano can last for thousands of years, or it can go on for millions of years, with regular eruptions. Many of Earth‘s volcanoes have had dozens of eruptions in the last few thousand years, but they’ve been quiet for recorded history, and have large populations built up around their base. The Smithsonian Global Volcanism Program defines a volcano as active if it has had an eruption within the last 10,000 years or so.
And so a dormant volcano is actually part of the active volcano classification, it’s just that it’s not currently erupting.
When a volcano becomes cut off from its magma supply, that’s when it finally stops erupting and becomes an extinct volcano.
Sunday, November 28, 2010
Vocabulary: Active, dormant and extinct volcanos
From Universe Today: Difference Between Active and Dormant Volcanoes
Friday, November 26, 2010
How many volcanoes are there in Alaska?
From the Alaska Volcano Observatory website:
Alaska contains over 130 volcanoes and volcanic fields which have been active within the last two million years.These volcanoes are catalogued at their website: http://www.avo.alaska.edu/volcanoes.
Of these volcanoes, about 90 have been active within the last 10,000 years (and might be expected to erupt again), and more than 50 have been active within historical time (since about 1760, for Alaska).
The volcanoes in Alaska make up well over three-quarters of U.S. volcanoes that have erupted in the last two hundred years.
Alaska's volcanoes are potentially hazardous to passenger and freight aircraft as jet engines sometimes fail after ingesting volcanic ash.
It is estimated that more than 80,000 large aircraft per year, and 30,000 people per day, are in the skies over and potentially downwind of Aleutian volcanoes, mostly on the heavily traveled great-circle routes between Europe, North America, and Asia. Volcanic eruptions from Cook Inlet volcanoes (Spurr, Redoubt, Iliamna, and Augustine) can have severe impacts, as these volcanoes are nearest to Anchorage, Alaska's largest population center.
The series of 1989-1990 eruptions from Mt. Redoubt were the second most costly in the history of the United States, and had significant impact on the aviation and oil industries, as well as the people of the Kenai Peninsula.
On the Kenai Peninsula, during periods of continuous ash fallout, schools were closed and some individuals experienced respiratory problems. At the Drift River oil terminal, lahars and lahar run-out flows threatened the facility and partially inundated the terminal on January 2, 1990. The Redoubt eruption also damaged five commercial jetliners, and caused several days worth of airport closures and airline cancellations in Anchorage and on the Kenai Peninsula. Drifting ash clouds disrupted air traffic as far away as Texas.
The three eruptions of Mt. Spurr's Crater Peak in 1992 deposited ash on Anchorage and surrounding communities, closed airports, made ground transportation difficult, and disrupted air traffic as far east as Cleveland, Ohio. More information about this eruption is available here. Many older Alaskans also remember ash falling on Anchorage during the 1953 eruption of Mt. Spurr's Crater Peak.
The 1912 eruption of Novarupta and Katmai, which formed the Valley of Ten Thousand Smokes on the Alaska Peninsula, was the largest 20th-century eruption on earth, and the largest historical eruption in Alaska. Ash from Novarupta spread worldwide, and is often still remobilized by strong winds. Roofs in Kodiak collapsed due to the weight of the ash; six villages close to Katmai and Novarupta were permanently abandoned. More information about this eruption is available here.
How often do Alaskan volcanoes erupt?
Although the historical record in Alaska goes back to about 1760 (there are a few earlier eruption accounts), the task of counting known eruptions and calculating an eruption frequency is complicated by the sparse and often inaccurate older accounts.
Many times, a volcano is reported as "smoking" without further clarification of what that smoke may have been - a real eruption, normal fumarolic activity, or even atypically tall clouds rising above a summit because of unstable weather conditions. The term "eruption" as used here includes vigorous explosions which may not contain fresh (juvenile) magma, as well as magmatic explosions and the effusion of lava as flows and domes.
Since 1760, 27 Alaskan volcanoes have had more than 230 confirmed eruptions. This averages to nearly one eruption per year. If we add in those volcanoes and eruptions that are suspected but unconfirmed (and often, unconfirmable), then we have 54 volcanoes with about 424 possible eruptions, yielding an average of 1.7 eruptions per year.
However, these figures do not consider the large discrepancy in observation and reporting of Alaskan eruptions. For the past 40 years - a period in which we have fairly good records -- Alaska has averaged more than two eruptions per year.
Alaska contains over 130 volcanoes and volcanic fields which have been active within the last two million years.These volcanoes are catalogued at their website: http://www.avo.alaska.edu/volcanoes.
Of these volcanoes, about 90 have been active within the last 10,000 years (and might be expected to erupt again), and more than 50 have been active within historical time (since about 1760, for Alaska).
The volcanoes in Alaska make up well over three-quarters of U.S. volcanoes that have erupted in the last two hundred years.
Alaska's volcanoes are potentially hazardous to passenger and freight aircraft as jet engines sometimes fail after ingesting volcanic ash.
It is estimated that more than 80,000 large aircraft per year, and 30,000 people per day, are in the skies over and potentially downwind of Aleutian volcanoes, mostly on the heavily traveled great-circle routes between Europe, North America, and Asia. Volcanic eruptions from Cook Inlet volcanoes (Spurr, Redoubt, Iliamna, and Augustine) can have severe impacts, as these volcanoes are nearest to Anchorage, Alaska's largest population center.
The series of 1989-1990 eruptions from Mt. Redoubt were the second most costly in the history of the United States, and had significant impact on the aviation and oil industries, as well as the people of the Kenai Peninsula.
On the Kenai Peninsula, during periods of continuous ash fallout, schools were closed and some individuals experienced respiratory problems. At the Drift River oil terminal, lahars and lahar run-out flows threatened the facility and partially inundated the terminal on January 2, 1990. The Redoubt eruption also damaged five commercial jetliners, and caused several days worth of airport closures and airline cancellations in Anchorage and on the Kenai Peninsula. Drifting ash clouds disrupted air traffic as far away as Texas.
The three eruptions of Mt. Spurr's Crater Peak in 1992 deposited ash on Anchorage and surrounding communities, closed airports, made ground transportation difficult, and disrupted air traffic as far east as Cleveland, Ohio. More information about this eruption is available here. Many older Alaskans also remember ash falling on Anchorage during the 1953 eruption of Mt. Spurr's Crater Peak.
The 1912 eruption of Novarupta and Katmai, which formed the Valley of Ten Thousand Smokes on the Alaska Peninsula, was the largest 20th-century eruption on earth, and the largest historical eruption in Alaska. Ash from Novarupta spread worldwide, and is often still remobilized by strong winds. Roofs in Kodiak collapsed due to the weight of the ash; six villages close to Katmai and Novarupta were permanently abandoned. More information about this eruption is available here.
How often do Alaskan volcanoes erupt?
Although the historical record in Alaska goes back to about 1760 (there are a few earlier eruption accounts), the task of counting known eruptions and calculating an eruption frequency is complicated by the sparse and often inaccurate older accounts.
Many times, a volcano is reported as "smoking" without further clarification of what that smoke may have been - a real eruption, normal fumarolic activity, or even atypically tall clouds rising above a summit because of unstable weather conditions. The term "eruption" as used here includes vigorous explosions which may not contain fresh (juvenile) magma, as well as magmatic explosions and the effusion of lava as flows and domes.
Since 1760, 27 Alaskan volcanoes have had more than 230 confirmed eruptions. This averages to nearly one eruption per year. If we add in those volcanoes and eruptions that are suspected but unconfirmed (and often, unconfirmable), then we have 54 volcanoes with about 424 possible eruptions, yielding an average of 1.7 eruptions per year.
However, these figures do not consider the large discrepancy in observation and reporting of Alaskan eruptions. For the past 40 years - a period in which we have fairly good records -- Alaska has averaged more than two eruptions per year.
Wednesday, November 24, 2010
The Alaska Volcano Observatory
The website for the Alaska Volcano Observatory is: http://www.avo.alaska.edu.
From their website:
The Alaska Volcano Observatory (AVO) is a joint program of the United States Geological Survey (USGS), the Geophysical Institute of the University of Alaska Fairbanks (UAFGI), and the State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO was formed in 1988, and uses federal, state, and university resources to monitor and study Alaska's hazardous volcanoes, to predict and record eruptive activity, and to mitigate volcanic hazards to life and property.
AVO has three primary objectives:
--To conduct monitoring and other scientific investigations in order to assess the nature, timing, and likelihood of volcanic activity;
--To assess volcanic hazards associated with anticipated activity, including kinds of events, their effects, and areas at risk; and
--To provide timely and accurate information on volcanic hazards, and warnings of impending dangerous activity, to local, state, and federal officials and the public.
AVO offices are in Anchorage and Fairbanks, Alaska. The Anchorage office is at the USGS, and is the primary point of information dissemination during crises. Fairbanks offices are concentrated at the UAFGI, which serves as the data collection point for most of the seismic and satellite data. AVO is staffed by the equivalent of about 22 full-time scientists, technicians, and administrators. Managerial responsibility for AVO rests with the Scientist-in-Charge, a USGS employee in Anchorage, and the Coordinating Scientist in Fairbanks, a UAFGI or ADGGS employee.
Tuesday, November 23, 2010
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