Erin Zimpfer Dustin Brown ` Alisha Kimbro
Lithosphere Reactions
1. The Eastern side of the Philippine plate is a convergent boundary with the Pacific plate, at this boundary the Pacific plate sub ducts beneath the Philippine plate. http://volcano.und.edu/vwdocs/volc_images/southeast_asia/philippines/tectonics.html As the plates move towards each other, friction occurs. This friction causes a build-up of pressure, which when released results in a series of earthquakes. The plates must release this pressure due to the elastic rebound theory. (EES 345)
A year prior to the eruption was when the release of pressure occurred in the form of a major earthquake. This major earthquake hit 7.8 on the Richter scale, which is comparable to the great 1906 California earthquake. As a result there was a landslide, some local earthquakes, and a short-lived increase in steam emissions. By early the next year, subsequent earthquakes had forced magma from deep below, up through the chamber of the dormant volcano. Following this movement of magma, steam explosions occurred resulting in three holes in Mt. Pinatubo’s north side. This cycle of earthquakes, magma movement, and steam emission continued until the reawakening in June 1991. http://pubs.usgs.gov/fs/1997/fs113-97/
2. The major eruption that finally occurred in the summer of 91 lasted for nine hours. As a result, Mt. Pinatubo’s summit collapsed. The mountain’s summit fell from 1745 meters to 1485 meters due to the expulsion of magma and the creation of a caldera. This deformation of the mountain caused a chain of earthquakes that continued to cause havoc on the surrounding area. http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
3. The eruption had devastating effects. The cloud of ash that was emitted by the volcano was 250 miles wide and 21 miles high. The ash from this cloud covered an area of 2,900 square miles to a depth of .4 inches or more with a maximum thickness at 20 inches. The volume of the ash was 1.2 cubic miles. http://pubs.usgs.gov/fs/1997/fs113-97/ Fine ash was carried by the wind, and fell as far as the Indian Ocean, and satellites followed the ash cloud several times around the globe. http://pubs.usgs.gov/fs/1997/fs113-97/
4. On top of the ash fall, pyroclastic flows or hot gases and rock fragments that are discharged from the volcano flowed down. This flow takes the place in the ash in the sky and the basal flow of fragments that flow along the land. This basal flow destroyed the nearby vicinity, and with speeds that can reach upwards of 50 miles per hour, the flows destroy or carry with it nearly everything in its path. http://volcanoes.usgs.gov/Hazards/What/PF/pcflows.html These extremely hot flows of ash sterilized 154 square miles or land around the volcano, filling valleys with high-temperature deposits as much as 660 feet thick. http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/description_pinatubo.html
5. At the time of the explosion, the region was experiencing heavy rainfall due to Typhoon Yunya. The heavy rain created lahars similar to when snow capped mountains melt due to an explosion. http://pubs.usgs.gov/pinatubo/major/index.html The flooding that was produced from the typhoon stirred up the ash and flow deposits. These deposits are subject to rapid removal when exposed to water, so with the heavy rain falling on the deposits, mud flows or lahars were created which filled in streams and river valleys around the mountain. http://www.britannica.com/eb/article-253601/volcano Lahars thickness can vary between thick water and wet concrete, while potentially removing anything in its path like bridges, highways, houses, etc.
6. Due to the high amounts of ash, pyroclastic flows and the lahars, there was almost one half of a billion dollars in property and economic damage. http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm The pyroclastic flows destroyed lots of vegetation, and the surface or landscape around and near the volcano. This can cause famines in the area, which are the largest indirect hazard produced by a volcanic eruption. (Bryant, 1991 and Francis, 1993). Although these hazardous effects from a volcano are destructive, there are some positive outcomes. The tephra or deposits that were produced during the eruption are very benefical to the soil, for It produces fertile land for crops to regrow. This fertile land of soil is on the of main reasons why people are able to live on or near active volcanoes. They know it is dangerous, but that is how they can survive and make a living for themselves. http://www.geo.mtu.edu/volcanoes/hazards/primer/tephra.html