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From: Chris Higginbottom
Date: 10/29/02
Time: 12:32:48 PM
Remote Name: 216.109.17.62
What is the lithosphere?
The lithosphere contains all of the cold, hard solid land of the planet’s crust or surface, the semi-solid land underneath the crust, and the liquid land near the center of earth. The surface of the lithosphere is very uneven because it includes the mountain ranges (the Rockies and Andes), the plains or flat areas that are found in Iowa, Texas, and Brazil, and the deep valleys of the ocean floor. The lithosphere thins to a few kilometers at ocean spreading centers, thickens to about 100 to 150 kilometers under the ocean basins, and is up to 250-300 kilometers thick under continental shield areas. The crust is an important part of the lithosphere; however, it is composed mainly of mantle rocks. Due to this, authors sometimes state that the lithosphere is the uppermost part of the mantle and they do not include the thin rocks of the crust.
www.geolsoc.org.uk/template.cfm%3Fname%3Dlithosphere
http://distnace.una.edu/ess/5-8/cintro/spheres.html
What is the Larsen Ice Shelf?
Ice shelves are thick plates of ice that are fed by glaciers then float around much of Antarctica. The Larsen Ice Shelf was about 220 meters thick and is believed to have existed for at least 400 years. Recent satellite imagery has shown that the northern section of the ice shelf has broken and separated from the continent in the largest single event in a thirty year series of ice shelf retreats in the Antarctic Peninsula. This has caused thousands of icebergs to float in the Weddell Sea, which is east of the Antarctic Peninsula. A total of about 1,250 square miles of ice shelf area has disintegrated in a thirty-five day period that began on January 31, 2002. Scientists believe these retreats have been caused by an increase in climate warming. The temperatures of the Antarctic have increased about 2.5 degrees Celsius since the late 1940s. Since 1974 the ice shelf extent in the Peninsula has declined by about 5,200 square miles.
http://www.eurekalert.org/pub_releases/2002-03/uoca-ais031802.php
Event>Sphere Interactions
E>L The disintegration of ice shelves can change the coastal grounding line they are attached to and also the surrounding islands or rocks. When the glaciers move out over the ocean, they pass over rocky terrain and anchor to the rocks to form a hinge. They also attach to the land surface of the continent and form a grounding line. The ice shelves float up and down with the ocean waves and grate against the rocks. This causes the rocks to become smoother and eventually break apart. The sediments that result from this will then settle on the bottom of the ocean or they will be carried away by the iceberg that develops when the ice breaks away. If the erosions continue, the rocks will break apart and will not be able to provide a breaking system for the ice shelf. The ice shelves prevent the discharging of glaciers in the ocean.
The grounding line may also be affected. When the Ninnis Glacier Tongue on the eastern coast of Antarctica broke away it changed the coastline overnight. When the tongue disintegrated it cracked at the grounding line and moved away from the land. This caused pieces of rock and sediments to be pulled away from the grounding line, therefore changing the shape of the coastline.
http://earthobservatory.nasa.gov/Study/Ninnis/
E>L The disintegration of the ice shelves will cause the Antarctic continent to rise above sea level. The Antarctic icecap contains about 90 percent of the ice that exists in the world and 70 percent of the world’s fresh water. The weight of the ice in the Antarctic is so great in many areas that it pushes the land below sea level. This process is known as isostasy. If the ice shelves were to collapse, this could cause severe problems because the ice shelf acts as a braking system for some of the very large glaciers. With rising temperatures and global warming, the glaciers would start to flow at faster rates into the oceans.
http://www.usatoday.com/weather/antarc/aiceshet.htm
http://www.antarctica.ac.uk/Key_Topics/IceSheet_SeaLevel/
E>L The disintegration of the ice shelves can cause pollutants to be carried to other lands and contaminate the soil. Sea ice seems to be a key element in the transport of contaminants. If the water is contaminated and frozen into ice these contaminants will be released into the ocean as the ice thaws, refreezes, and thaws again. As the sea ice flows into warmer water and melts, the contaminated sediments can flow to nearby shores and pollute the soil. This could then prevent plants from being able to grow, etc. and as rain washes the soil into the ocean, the ocean could then be polluted as well.
http://www.ecology.com/ecology-today/tracking-air-pollution/
E>L The land may rise or sink as the ice shelves disintegrate. Isostatic rebound occurs when a load is imposed on or removed from the lithosphere. The surface tends to either rise or sink as the lithosphere rises or sinks into the asthenosphere. Loads may include lakes, oceans, ice, sediment, or volcanoes. The rising and sinking of the lithosphere may continue until isostatic equilibrium is reached.
http://www.umich.edu/~gs265/isost.html
E>L The event may cause a peripheral bulge. Isostatic depression itself is only possible if the asthenosphere can flow away from the depressed area and if the lithosphere is able to move vertically, either along fractures or by elastic bending. Geological evidence indicates that lithospheric bending dominates over fracturing and we can therefore use flexural models to predict the shape of the depression and surrounding areas (or vice versa). Instead of all areas around a load becoming depressed, the flexural rigidity of the lithosphere (among other things) causes some areas to actually be elevated during this same time. This is known as the peripheral bulge, which forms a ring around the outside of the load.
http://www.umich.edu/~gs265/isost.html
E>L Coastal flooding may result as the ice melts. Some estimates of how much flooding there would be include 35 meters ocean rise to 75 meters rise. Still other estimates state a rise of 60-110 meters. This flooding could cause coastal erosion which could result in the loss of coastal cities as buildings and homes are destroyed.
http://maxpages.com/globalwarming
http://www.pog.su.se/sea/04_coastal.htm
Event to Sphere Interactions
L>E Along the edge of the coastal line are rocks that could cause the ice shelves to break apart. The glaciers often grind past these rocks and cause cracks and crevices to appear in the ice. If the ice plows into the rocks, the ice shelf could be destroyed.
http://earthobservatory.nasa.gov