GENERIC FEATUREs

A volcanic vent is an opening exposed on the earth's surface where volcanic material is emitted. All volcanoes contain a central vent underlying the summit crater of the volcano. The volcano's cone-shaped structure, or edifice, is built by the more-or-less symmetrical accumulation of lava and/or pyroclastic material around this central vent system. The central vent is connected at depth to a magma chamber, which is the main storage area for the eruptive material. Because volcano flanks are inherently unstable, they often contain fractures that descend downward toward the central vent, or toward a shallow-level magma chamber. Such fractures may occasionally tap the magma source and act as conduits for flank eruptions along the sides of the volcanic edifice. These eruptions can generate cone-shaped accumulations of volcanic material, called parasitic cones. Fractures can also act as conduits for escaping volcanic gases, which are released at the surface through vent openings called fumaroles.

Summit Crater

Parasitic Cones

Fumarole

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MAIN VOLCANO TYPES
Although every volcano has a unique eruptive history, most can be grouped into three main types based largely on their eruptive patterns and their general forms. The form and composition of the three main volcano types are summarized here:



VOLCANO
TYPE
VOLCANO
SHAPE
COMPOSITION
ERUPTION
TYPE

SCORIA CONE

Straight sides with steep slopes; large summit crater
Basalt tephra; occasionally andesitic
Strombolian

SHIELD VOLCANO

Very gentle slopes; convex upward
Basalt lava flows
Hawaiian

STRATOVOLCANO

Gentle lower slopes, but steep upper slopes; concave upward; small summit crater
Highly variable; alternating basaltic to rhyolitic lavas and tephra with an overall andesite composition
Plinian

SUBORDINATE VOLCANO TYPES -- Lava and tephra can erupt from vents other than these three main volcano types. A fissure eruption, for example, can generate huge volumes of basalt lava; however, this type of eruption is not associated with the construction of a volcanic edifice around a single central vent system. Although point-source eruptions can generate such features as spatter cones and hornitos, these volcanic edifices are typically small, localized, and/or associated with rootless eruptions (i.e., eruptions above the surface of an active lavaflow, unconnected to an overlying magma chamber) . Vent types related to hydrovolcanic processes generate unique volcanic structures, discussed separately under hydrovolcanic eruptions.

For a description of each of the main volcano types, see:

SCORIA CONES
SHIELD VOLCANOES
STRATOVOLCANOES

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WHEN IS A VOLCANO CONSIDERED ACTIVE, DORMANT, OR EXTINCT?
Classifying a volcano as active, dormant, or extinct is a subjective and inexact exercise. A volcano is generally considered active if it has erupted in historic time. This definition, however, is rather ambiguous, because recorded history varies from thousands of years in Europe and the Middle East, to only a few hundred years in other regions of the world, like the Pacific Northwest of the United States. Scientists generally consider a volcano active if it is currently erupting, or exhibiting unrest through earthquakes, uplift, and/or new gas emissions. The Smithsonian Institution's catalog of active volcanoes, recognizes 539 volcanoes with historic eruptions. In addition, there are 529 volcanoes that have not erupted in historic times, but which exhibit clear evidence of eruption in the past 10,000 years. These latter volcanoes are probably best considered "dormant," since they have the potential to erupt again.

Whether or not inactive volcanoes are considered truly extinct, or just dormant, depends partly on the average repose

A Collaborative Higher Education, K-12, and Public Outreach project
of the North Dakota and Oregon Space Grant Consortia
administered by the Department of Geosciences at Oregon State University


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Legends Lost

VolcanoWorld is deeply saddened by the recent loss of Dr Jim Luhr. Jim directed the Smithsonian's Global Volcanism Program from 1995 to the present, and was a great supporter of VW. Jim was always generous with his advice and unfailing in his enthusiasm and understanding of the importance of public- and educational outreach. This is a great loss to us, and the volcanological and geological community as a whole. Our condolences go out to his family. For additional information, please visit http://www.volcano.si.edu/luhr.cfm


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Amazing Volcano Images Added!



Long time VW friends Steve & Donna O'Meara of Volcano Watch International have kindly provided Volcano World with some amazing photographs of volcanoes from around the world. We are most grateful for their contribution and continued support. Click here to see their new images!

To see even more of their amazing photographs and video footage of volcanic eruptions, visit:
www.photoresearchers.com
www.superstock.com
www.ngdigitalmotion.com


Also check out the great new photographs of Mount St. Helens taken by our own resident volcano expert Shan de Silva!
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'RSS Site Feeds!'

VW is happy to provide a site feed of the SI/USGS current eruptions and our "RAQ's" (Recently Asked Questions)

(Note: Direct site feeds need a 'reader' program such as Google Reader or a RSS capable browser (such as Opera))


Current Eruptions


Click above to directly subscribe to the RSS Feed or add VW eruptions to your homepage by clicking below:





RAQ's
(Recent Questions Emailed to VW)


Click above to directly subscribe to the VW RAQ (Recently Asked Question's) feed or add it to your homepage by clicking below:







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L'IZTACCIHUATL et Le POPOCATEPETL


'Legends of the Volcano'

VW students and staff have completed the first round of work updating the 'Legends of the Volcano' section! This section focuses on the myths and legends surrounding volcanoes in many cultures throughout the world. This is an ongoing VW project and we are interested in your input and local volcano stories!!

Click this link to read more Legends of the Volcano!


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Science Netwatch:
Information Eruption!

Volcano World was mentioned in the netwatch section of the December 23rd issue of Science Magazine (Vol. 310. no. 5756, p. 1877). VW would like to thank netwatch editor Mitch Leslie for this honor. Science magazine is an exciting and interesting weekly publication of the American Association for the Advancement of Science. Click here to read the full story. (Requires Adobe Acrobat Reader - Download plug-in here.)


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VW Wins GeoSciences Information Society
2005 Best Website Award!!

Congratulations to Rocky and the Staff of VW for winning the GeoSciences Information Society's "Best Website Award for 2005."

This year, they decided upon two winners, one for the general public and the other for academia. VW won the best general public website award.


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Space Imaging has kindly provided Volcano World with some excellent IKONOS satellite images of Earth's volcanoes. We are grateful for their contribution and support.


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Biography for
Steven Seagal

Nickname
The Great One
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Height
6' 4" (1.93 m)
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Mini biography
Tall, striking and somewhat boyishly handsome looking (often with ponytail), and usually impeccably dressed action star who burst onto the martial arts film scene in 1988 in the fast paced Warner Bros. production _Above The Law (198 _ . The enigmatic Seagal commenced his martial arts training at the age of 7, under well known karate instructor and author Fumio Demura and in the 1960s commenced his aikido training in Orange County under the instruction of Harry Ishisaka. Seagal received his first dan accreditation in 1974, after he had moved to Japan to further his martial arts training. After spending many years there honing his skills, he achieved the ranking of a 7th dan in the Japanese martial art "aikido" and was instructing wealthy clients in Los Angeles when he came to the attention of Hollywood power broker Michael Ovitz.

Ovitz saw star value in the imposing looking Seagal, plus the high octane action movie genre was in full swing in the late 1980s and Seagal's debut movie was wildly received by action fans! Seagal followed up Above the Law (198 with another slam bang thriller in Hard to Kill (1990) as a gunned down cop who revives from a coma to strike back at the mob. The movie also starred leggy Kelly LeBrock who would wind up married to Seagal from 1987 to 1996, and mother to three of his children. His next outing was battling voodoo wielding, Jamaican drug gangs in the hyper violent _Marked For Death (1991)_ , before returning to fight psychotic mob gangster William Forsythe in the even more punishing Out for Justice (1991). Seagal was by now enormously popular, and his next movie, Under Siege (1992) set aboard the battleship USS Missouri, and additionally starring Tommy Lee Jones and Gary Busey was arguably his best film to date!

Seagal's fighting style was rather different from that of other on screen martial arts dynamo's such as Bruce Lee, Chuck Norris and 'Jean Claude van Damme' who were predominantly fighters from striking arts background such as karate or tang soo do. However, aikido is built around using an opponents inertia and bodyweight to employ various locks, chokes & holds that incapacitate them. Seagal carries himself differently too, and often appears wearing Italian designer clothes and he usually favours an all black outfit, generally with a three quarter length coat with an elaborate trim. Additionally, Seagal's on screen characters were often seemingly benign or timid individuals, however when the going gets rough they then reveal themselves to be deadly ex-CIA operatives, or retired Special Forces soldiers capable of wholesale destruction!

With his box office drawing power, Seagal then began to influence his film projects to reflect his personal & spiritual beliefs, especially concerning the abuse of the environment. He appeared as an oil fire expert who turns against his corrupt CEO (played by Michael Caine) in On Deadly Ground (1994) to save the Eskimo population from an oil disaster, in Fire Down Below (1997) he plays an environmental agency troubleshooter investigating the dumping of toxic waste in Virginian coal mines, and in the slow moving The Patriot (1998/I) he plays a medical specialist trying to stop a lethal virus unleashed by an extremist group.

Action fans struggled to come to terms with social messaging being built into bone crunching fight films, however Seagal's box office clout remained fairly strong, and more traditional chop socky projects followed with the "buddy cop" film The Glimmer Man (1996), then almost a cameo role as a Navy Seal alongide CIA analyst Kurt Russell, before Seagal is sucked out of a jet at 35,000 feet in Executive Decision (1996).

In 1999, Seagal took a different