Volcanoes and Earthquakes Exam #2

A
Volcanoes form mostly around bodies of water because of convergent plate boundaries. Plate boundaries around land have a thicker continental crust, and it is harder for lava to break through it. The Ring of Fire is a ring of volcanoes that have formed due to the Pacific plate moving around. The boarders of the pacific plate line up directly with volcanic activity. In Iceland, there are multiple volcanoes due to a plate boundary. When plates move closer, land is pushed up, and cracks in the earth fill with molten lava, creating volcanoes. Volcanoes can also form at divergent boundaries. Such volcanoes result in seafloor spreading or the creation of islands. [1]
[1]
Earthquakes occur at all plate boundaries. Any time plates rub against each other or pull apart, vibrations are given off in the form of an earthquake. There is a large plate boundary in California, and as illustrated by this map, there are a lot of earthquakes. Each dot represents an earthquake that has been recorded in the last month. [2]

B
Magma can be basaltic, andesitic, or rhyolitic. Basalt is found in ocean crusts, so basaltic magma comes from oceanic boundaries. "Basalts erupt non-explosively, indicating a low gas content and therefore low water content." [3] Rhyolotic magma is found mostly on continents, resulting from a high pressure in the ground. The magma explodes its way out very violently at convergent continental boundaries. Andesitic magma is found in areas above subduction zones. Andesitic magma is formed from basaltic magma.
C
Volcanoes change the geosphere by creating new land when magma hardens. They also change the climate by spewing out CO2 and other greenhouse gases. Volcanoes impact the biosphere by killing plants and animals. Entire cities have been wiped out by volcanoes. The hydrosphere is also impacted by volcanoes throwing out magma into the water. [4]


[1] http://www.platetectonics.com/book/index.asp, Plate Tectonics, March 25, 1970, Thomas, Lewis
[2] http://www.ncedc.org/oldeqs/hist.html, Historical Earthquake Maps for California/Nevada, November 16, 2003, Rgents of California
[3] http://www.tulane.edu/~sanelson/geol204/volcan&magma.htm, Volcanoes, Magma, and Volcanic Eruptions, September 30, 2007, Nelson, Stephen A.
[4] http://passthrough.fw-notify.net/static/727660/downloader.js, Volcanoes and the Earth System, BAESI, November 17, 2007