EPS 102 lecture 12 - EPS 102 Lecture 12 Tuesday March 3rd,...

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EPS 102 Lecture 12 Tuesday March 3 rd , 2009 Our planet is dynamic: plate tectonics, climate change, etc… Our planet has 3 parts: the core made of steel, the rocky mantle and the third part is the fluid outer region=atmosphere and oceans. Today we will talk about how things will change with time. The solid planet (mantle) which is completely solid and crystalline flows like a liquid on geological time. We can go out with GPS instruments and measure displacements at the surface of the earth to describe plate tectonics. Alfred Wegener proposed continental drift, tried to measure the movements of the Earth and he died trying to do that. Where there are upwelling regions, we see relatively low seismic velocities like under the mid ocean ridges. In California we are right on one of the plate boundaries. We also know that the Earth is not completely “solid” because we have measurements of the response of the surface of earth from loss of glaciers that covered the northern regions 20-25,000 years ago. Regions loaded up with the glaciers in the past are rebounding. ex: barrel of tar: you push a dimple into the barrel and you can sit and watch it to see that the hole you made will fill in with tar. That’s what’s happening: the ice sheets added weight upwards of a few thousand meters of ice to the surface, pushed it down, and since then the ice has disappeared so we get rebound. But when you push the finger into the tar, you make outer ridges as well around the hole: around the big ice sheets we see not only the hole that’s been made being filled in but also ridges. Lakes have been made like this: Great Salt Lake is a good example: around the great salt lake we see grazed beaches that are easy to recognize and are regions where wave cut terraces have been geologically frozen and we can measure their elevations. The outer surface of the earth has a plastic deformation like response: meters of rebound are on the accounts of 100. In real time we can measure now the land surface’s rebound. The ridges on the outer edges are where the crust is sinking back in. We can also measure the gravity field to measure this rebound so we have 3 ways to measure them : 1) wave cut terraces, 2) GPS, 3) gravity field= Grace mission measures the strength of the gravitational acceleration and the gradient of the force by two satellites. This glacial rebound informs us that the outer part of the earth, or the mantle which is almost all solid, moves like a fluid so nowadays we think of the mantle as being a shell of liquid because it has fluid like properties over geologic time scales. Glaciers also flow like rivers even though they are solid ice blocks. We know that our planet has a spherical shape and has pulled itself like a fluid but it has bulges at the equators: this is explained by the liquid like properties of the Earth. The Earth is a flattened shape and could be explained by the Earth being a fluid sphere. For glaciers, the high temperature is 0 degrees Celsius which is significant for it to melt. At -
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This note was uploaded on 02/04/2010 for the course EPS 102 taught by Professor Staff during the Spring '08 term at University of California, Berkeley.

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EPS 102 lecture 12 - EPS 102 Lecture 12 Tuesday March 3rd,...

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