STRATOVOLCANO

Mt Rainier from the west. Stan Shebs. 11/13/13 (http://commons.wikimedia.org/wiki/File:Mount_Rainier_from_west.jpg)

INTRODUCTION Stratovolcano, otherwise known as composite cones, are the most picturesque and dangerous of volcanoes. These dangerous structures have been the cause of much death and loss of property. Many of these volcanoes lie near well populated areas making understanding them very important.

Mt.fuji from R469. Yuno-yuno, 23 May 2007 (http://commons.wikimedia.org/wiki/File:Mt_fuji%28R469_Yuno%29.jpg

SHAPE Stratovolcano are characterized by shallow slopes that increase in angle as you approach the summit.

These volcanoes are dotted with many secondary vents along there surface

In general, stratovolcanoes have small summit craters.

Stratovolcanoes may differ in shape dramatically due to composition or violent past eruptions i.e. Mt. St. Helens

http://www.decadevolcano.net/photos/keywords/stratovolcano.htm

CREATION Stratovolcano take tens of thousands to hundreds of

thousands of years to form. Most currently active volcanoes of this type are less than

100,000 years old, but some, such as Mount Rainier are possibly over a million

These volcanoes alternate between eruptions of pyroclastic material and lava flows. This variation allows the volcano to grow to tremendous heights.

The materials extruded from these volcanoes can range from fine grained basaltic flows to coarse grained rhyolitic flows in the same volcano. However, the most common composition is andesite.

http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/volcschema_page.html

CREATION CONT. Stratovolcano typically form at convergent boundaries,

where two plates meet and one is subducted beneath the other.

Subduction zones are found in abundance along the rim of the pacific ocean in a region known as ‘the Ring of Fire’ Mt. St. Helens, Mt. Rainier, Mt. Hood, the Aleutian islands, and the

Andes mountain range in South America are all stratovolcano ranges located along the ring of fire.

11 February 2009, http://upload.wikimedia.org/wikipedia/commons/5/52/Pacific_Ring_of_Fire.svg

MT. ST. HELENS On March 16, 1980 earthquakes began to rumble beneath

the surface of Mt. St. Helens. A bulge began to form indicating activity in the volcano.

On March 18, following an earthquake, the volcanos summit and bulge slid away, causing the largest landslide in recorded history, and depressurizing the magma system within.

The subsequent explosion shot ash and debris to the north at 300 mph.

An hour later massive pyroclastic flows flowed five miles to the north.

The resulting cloud of ash spread far eastward and left Spokane, Washington in complete darkness 250 miles away.

Lyn Topinka, 19 May 1982 (http://en.wikipedia.org/wiki/File:MSH82_st_helens_plume_from_harrys_ridge_05-19-82.jpg)

MT. VESUVIUS Mount Vesuvius is the only active volcano in mainland

Europe Vesuvius is “fueled” by the subduction of the African

plate beneath the Adriatic Sea. Vesuvius is most commonly known for its 79 A.D.

eruption that destroyed Pompeii and Herculaneum. The eruption of Vesuvius in 79 A.D. is estimated to have

killed 16,000 people, burying them in hot ash. Mt. Vesuvius last erupted in 1944, during world war II,

causing problems for the newly arrived allied forces.

http://blog.otel.com/top-ten-famous-volcanoes/mt-vesuvius/

KRAKATOA Krakatoa is a stratovolcano located in the Indonesian island arc In it’s historic 1883 eruption 36,000 people are estimated to have

been killed, due to thermal injury from the blast or from the tsunamis that occurred when the volcano collapsed into the caldera.

The volcanic activity of Krakatoa is caused by the subduction of the Indo-Australian tectonic plate into the Eurasian plate.

The eruption could be heard as far away as Perth, Australia, more than 2,500 miles away.

The force of the eruption is estimated at 2,000 megatons. (10,000 times larger than the explosion at Hiroshima)

The resulting cloud of ash reduced the worlds temperature by around 1.2 degrees farenheight for the next five years.

Nearby mount Tambora had an even larger explosion that reduced global temperatures by 5 degrees

MT. RAINIER Mt. Rainier is known as Americas most dangerous

volcano Rainier’s danger comes not from a possible eruption, but

rather from a hollow interior 5,600 years ago, the top portion of Mt. Rainier collapsed

into a massive lahar, flowing over 100 miles to Puget Sound.

Around 150,000 people live atop these ancient mud flows, and many more live in the cities of Seattle and Tacoma directly adjacent to the volcano.

The people in the area surrounding Mt. Rainier have prepared evacuation routes and watch the mountain closely, waiting for the possible collapse.

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<http://basicplanet.com/stratovolcano/>. Camp, V.. N.p.. Web. 13 Nov 2013.

<http://www.geology.sdsu.edu/how_volcanoes_work/stratovolc_page.html>.

Brantley, S., and B. Myers. N.p.. Web. 13 Nov 2013. <http://pubs.usgs.gov/fs/2000/fs036-00/>.

Ball, J.. N.p.. Web. 13 Nov 2013. <http://geology.com/volcanoes/vesuvius/>. Fink, M.. N.p.. Web. 13 Nov 2013.

<http://www.pbs.org/wnet/savageplanet/01volcano/03/indexmid.html>.