2007-03-19 08:41:31 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Earth Sciences & Geology
The land was crushed downwawrd by more than a kilometer of ice in someplaces. Continental masses can be thought of as floating on the mantle. The ice of the glacier pushed down the continent. When the ice melted, the continent rebounded upward similar to a rubber ducky that you held underwater and then let go only much much more slowly. There is a static friction that will tend to hold the land down but when the upward forces are great enough to exceed that static friction, the land rebounds upward toward its former elevation. We have been coming out of an ice age for 6000 years. It is a very slow process in the time scale of our lives.
2007-03-19 09:05:41 · answer #1 · answered by JimZ 7 · 1⤊ 0⤋
It is called isostatic rebound and it happens because the rock that makes up the earth's crust is less dense than the asthenosphere below. When you have a huge mass on top of the crust in a certain area (for example, the Antarctic ice sheet), the crust will be depressed into the asthenosphere - in fact, the lowest point in elevation on the planet that is not under the oceans is under the Antarctic ice sheet. When the ice sheet is gone this area will experience a great amount of uplift and the same areas that were once well below sea level will be well above it.
Think of it like pushing an ice cube down into a glass of water with your finger -- once you take your finger away, the ice cube comes back up to the top of the glass.
2007-03-19 15:57:56 · answer #2 · answered by brooks b 4 · 1⤊ 0⤋
The land is rebounding after being compressed under glaciers during the last ice age which ranged from 1-2 km high. The term used for this is called isostatic rebound.
2007-03-19 15:54:57 · answer #3 · answered by Sgt. Pepper 2 · 1⤊ 0⤋
Isostacy. During the Pleistocene there was a lot of ice on top of the northern parts of continents. The density of the mantle is about 3500 kg/m^3 while the continents are about 2700 kg/m^3. Add about 3 km of ice at 1000 kg/m^3 and the mantle starts to move due to the increased weight. Once the ice melts the reduction of weight allows the mantle to move back and the continents start to move upward, since they are less dense than the mantle.
2007-03-19 17:22:55 · answer #4 · answered by Amphibolite 7 · 1⤊ 0⤋
It is bouncing back from the compression that the great ice sheet placed on it during the last period of glaciation.
2007-03-19 15:45:43 · answer #5 · answered by Jerry P 6 · 1⤊ 0⤋