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Volcanoes
 

What is a Volcano?
Volcanoes are cracks or ruptures in the earth's crust through which molten (melted) rock, ash and gases rise to the surface.

There are different types of volcanoes. Cinder cones are usually short with steep slopes, and are formed by explosive eruptions of pumice, ash, and other debris. Shield volcanoes are wide and slightly flat. They are formed by successive flows of lava, usually over a long period of time. Stratovolcanoes can be tall and cone shaped, and are formed by a series of eruptions; some with lava, and some with mostly ash.



Stratovolcano
Mt Redoubt from the Cook Inlet

Stratovolcano

  • Stratovolcanoes are also known as a composite volcanoes. These types of volcanoes are cone shaped and have very steep sides. They are formed after ash and lava build up. Most will have a crater at the summit and a cluster of vents around it. Instead of lava just flowing out of the top of the volcano, lava flows from the other vents creating the layers on the volcano.  



Cinder cone volcano

 Cinder Cone Volcano

  • Cinder Cones are the simplest of all of these volcanoes. They are created from particles and blobs of congealed lava ejected from a single vent that is just piled around it. 




Shield Volcano

 Shield Volcano

  • Shield volcanoes are build from almost entirely of lava that is very runny and thin. The lava just pours out of vents and slowly cools as it runs down the volcano. Because of this, the volcano will be shaped like a dome with very rounded, slowing sides. 




Alaska is home to more than 40 active volcanoes (volcanoes that have had at least one eruption since 1760) and many more potentially active volcanoes. Many of Alaska's volcanoes occur along the Alaska Peninsula and Aleutian Island. They are part of what is called the "Ring the Fire" that surrounds much of the Pacific Ocean.



Ring of Fire showing the range over the Pacific Ocean.
mt augustine
Image Courtesy of Read, Cyrus (AVO/USGS)
Mt. Augustine

Alaska's Volcanoes

80 percent of the United States active volcanoes lie on Alaskan soil. Alaska boasts the planet's largest eruption in the last century: the 1912 eruption of Novarupta, 450 miles southwest of Anchorage in what is now Katmai National Park. The eruption occurred over a 60-hour period. It darkened the sky over much of the Northern Hemisphere for several days, and deposited a foot of ash on Kodiak Island, 100 miles away. When the eruption was finally over, more than 40 sq. miles of once lush, green land were buried under volcanic deposits as deep as 700 feet. Many small holes and cracks developed in the ash fall, which let gas and steam escape from heated ground below escape. The result was a landscape riddled by thousands of steam vents. When explorer Robert Griggs came to see the damage of the eruption in 1913, he was amazed at what he saw and named the area "The Valley of Ten Thousand Smokes." Today, the steam vents are gone, and the valley continues to recover. Visitors to the area can still see evidence of the eruption and are reminded of the awesome power and destruction volcanoes can unleash.

Pavlof volcano is one of the Alaska's most active volcanoes, with 41 eruptions reported since 1760. Pavlof erupted in 1986 and ash was sent 10 miles into the sky, causing black snow to fall on Cold Bay. Another recent eruption occurred in 1992, When Mt. Spurr sent ash and debris into the air and stopped air traffic in and out of Anchorage for several days.

There are several other volcanoes through out Alaska's National Parks. Lake Clark contains Iliamna and Reboubt volcanoes. Wrangell St. Elias has several active and non-active volcanoes within its boundaries. The Shield Volcano in Mount Wrangell, found in the largest National Park in the United States, Wrangell St. Elias. The Cinder Cone Volcano is Mount Veniaminof and the Stratovolcano is Mount Redoubt, found in Lake Clark National Park and Preserve. Bering Land Bridge holds the Imuruk Lake volcano fields and Espenberg Moors. There are many other parks that are home to volcanoes, such as Tongass National Forest, Alaska State Parks, and National Wildlife Refuges.



park-science-katmai-pdf
NPS
Alaska Park Science Publication, Volume 11

Current Volcano Events:

Did you know that last year, on June 5th and 6th we celebrated the 100th anniversary of the largest eruption in both the 20th and 21st centuries! 

For current volcanic activity please visit, http://volcanoes.usgs.gov/activity/status.php.

For more specific information about Alaskan volcanoes, visit the Alaska Volcano Observatory website at http://www.avo.alaska.edu/





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A graphic image of a calculator. The text reads Alaska public lands statistics. Did You Know?
In 2007, Alaska’s nonfuel raw mineral production was valued at $3.52 billion. While gold production led to a major boom in Alaska at the turn of the century, zinc production now outranks gold as Alaska's number one valued nonfuel mineral.