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From: Elizabeth Lackey
Date: 10/6/02
Time: 10:32:44 PM
Remote Name: 24.159.72.249
What is the lithosphere?
The earth is divided into three different chemical layers: the core, mantle, and crust. The core, composed mostly of iron and nickel, remains very hot after 4.5 billion years of cooling. The mantle (the middle layer) is rich in the elements iron, magnesium, silicon and oxygen. The crust is rich in the elements oxygen and silicon with lesser amounts of aluminum, iron, magnesium, calcium, potassium, and sodium. There are two types of crust: dense oceanic crust made of basalt, and continental crust made of lower density rock such as andesite and granite. The outermost layers of Earth can be divided by their physical properties into the lithosphere and athenosphere. The lithosphere is the rigid outer layer made of crust and uppermost mantle. It is the ‘plate’ in plate tectonic theory. Athenosphere is the part of the mantle that flows, that is, exhibits “plastic behavior” much like toothpaste in a tube. The flow of the athenosphere is part of mantle convection, which plays a major part in moving lithospheric plates. (“http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/pla...”)
The Lithosphere is the rigid inorganic portion of the Earth, which contains the crust, and between 80 to 100 km of the mantle. Thickness of the Lithosphere averages about 100km; however, the Lithosphere can be just a few miles under the oceans and up to 300 km beneath the continents. Comprising the Lithosphere are rocks, minerals and elements. The tree types of rocks are igneous, sedimentary, and metamorphic. Scientists have found within these rocks over 2,000 types of minerals and have also identified or created from these rocks over 112 elements, which are found on the periodic table. Resting on and supported by the semi-fluid Astenosphere, the Lithosphere is broken into several sections termed 'tectonic plates'. These plates, because of the viscosity of the Astenosphere, cause movement of the Lithosphere. Plate movements can be a few inches per year and in different directions. When plates collide with one another or slide over or under one another, these meetings have been identified as Earthquakes. Sometimes these meetings occur over weak or thin portions of the Lithosphere that have a large amount of magma. When this occurs, volcanoes can form. "http://visearth.ucsd.edu/" Wood, J.(1991). Volcanoes: Fires from below. Milwaukee, WI: Gareth Stevens Children's Books.
The lithosphere includes all the geologic forms on the Earth’s surface: sea floors, trenches, islands, plains, plateaus and mesas, valleys and basins, hills, mountains, and volcanoes, and all their parts. ("http://encarta.msn.com/encnet/refpages/refarticle.aspc?refid=7615")
What is a volcano?
A volcano is a result of a mountain or hill being created from eruptions through one or more openings. As magma, or molten rock below the earth’s surface, is formed, it begins to rise toward lower pressure regions. Before erupting, it tends to accumulate in magma reservoirs, or underground storage regions. Materials such as lava, tephra, or rock fragments, and gases are released from volcanic eruptions. Each eruption adds layers to the volcano. As this accumulation occurs, a topographic feature, such as a mountain, hill, plateau or crater, is formed. Earth’s volcanoes are mostly formed beneath the oceans. Volcanoes are so dangerous because they have very hot and fast-moving erupted materials, such as lava, falling ash, and other volcanic debris. ("http://encarta.msn.com/encnet/refpages/refarticle.aspc?refid=7615")
There are three major types of volcanoes: Cinder cone, shield, and the composite or stratovolcano. The simplest type of volcano is the cinder cone. It is built from particles and blobs of congealed lava ejected from a single vent. As gas-charged lava is blown violently into the air, it breaks up into small fragments that solidify and fall as cinders or scoria around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than one thousand feet above their surroundings. Scoria forms when blobs of gas charged lava thrown into the air cool in flight and fall as dark volcanic rock containing cavities created by trapped gas bubbles. ("http://vulcan.wr.usgs.gov/Glossary/CinderCone/description_cinder…")
Shield volcanoes are built almost entirely of fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad gently sloping cone with a shape similar to a warrior’s shield. Lavas also commonly erupt from vents along fractures that develop on the flanks of the cone. Some of the largest volcanoes in the world are shield volcanoes (Kilauea, Mauna Loa). ("http://vulcan.wr.usgs.gov/Glossary?ShieldVolcano/description_shield…")
Some of the earth’s grandest mountains are composite volcanoes, also called stratovolcanoes. Typically steep-sided cones, they are built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise 8,000 feet above their bases. Most composite volcanoes have a crater at the summit, which contains a central vent or group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone. The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the earth’s crust rises to the surface. The volcano is built up the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc. are added to its slopes. Composite volcanoes tend to erupt explosively and pose a great danger to nearby life and property. Composite cones like Mount St. Helens and Mount Pinatubo are frequently found along subduction zones where one plate is being pushed under the edge of another plate. (“http://Vulcan.wr.usgs.gov/Glossary?StratoVolcano/description_com...)
What is Mount Pinatubo?
Mount Pinatubo is a volcano located on the Philippine Island of Luzon. It erupted violently on June 15, 1991. Although it lay dormant for more than 500 hundred years, geologists recognized some signs a few months before the eruptions. The full blow of Mount Pinatubo was quite unexpected. Over 50,000 people were forced to evacuate and two major military bases were closed. Several hundred lives were lost as a result of the Mount Pinatubo eruption. ("http://earthobservatory.nasa.gov/Study/AstronautPinatubo")
CAUSAL LINKS:
E>L>B: Lava floods and lahars create long-lasting damage down slope. Forests, grazing lands, and farm fields would be destroyed by volcanic eruptions. Crops and livestock would be killed, which could lead to starvation of people and animals that depend on them. ("http://earthobservatory.nasa.gov/Study/AstronautPinatubo")
E>L>H>B: Fallen ash from the volcano smothers everything. This ash is heavily accumulated on the ground. After rainfall, the concrete-like mixture may collapse roofs and damage crops. ("http://encarta.msn.com/encnet/refpages/refarticle.aspc?refid=7615")
E>L>H>B: A volcano is a result of shifting plates. These shifting plates of the lithosphere can cause the ocean floor to shift as well, resulting in tsunamis, large seismic sea waves. Tsunamis may be deadly to people who live in low-lying coastal areas. ("http://encarta.msn.com/encnet/refpages/refarticle.aspc?refid=7615")
RESOURCES
"http://earthobservatory.nasa.gov/Study/AstronautPinatubo"
"http://encarta.msn.com/encnet/refpages/refarticle.aspc?refid=7615"
“http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/pla...”
"http://vulcan.wr.usgs.gov/Glossary/CinderCone/description_cinder…"
"http://vulcan.wr.usgs.gov/Glossary?ShieldVolcano/description_shield…"
“http://Vulcan.wr.usgs.gov/Glossary?StratoVolcano/description_com...”
Wood, J.(1991). Volcanoes: Fires from below. Milwaukee, WI: Gareth Stevens Children's Books.