Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
If you live in an area where winter roars its ugly head and plummets temperatures below zero, then you know the joy that comes with the arrival of spring and warm temperatures. But, what if the weatherman said spring wasn't scheduled for another 10 million years? Well, if that were the case, then you would be living in an ice age and be able to look forward to nothing but a prolonged period of cold with glaciers blanketing much of the earth.
Glacial Erosion and Deposition
Glaciers are huge moving mountains of ice that can directly affect the landscape in many ways. The carving and shaping of the land beneath a moving glacier is a process referred to as glacial erosion. As a glacier moves over the earth's surface, it plucks up rocks and sediment, which then get stuck to its belly and go along for the ride. These particles act like sandpaper and scratch the bedrock below. The removal or rocks and grinding of bedrock create entirely new landscapes.
Glacial erosion is responsible for some of the most stunning rock features in mountainous regions, such as glacial horns, with their sharp, angular peaks, and cirques that have round hollows with steep sides.
Glaciers carved out basins within bedrock that later filled with water, forming millions of lakes that exist to this day. Glaciers were responsible for turning many of the typical V-shaped valleys between the mountains into U-shaped valleys with broad and wide valley floors.
When the environment emerges from the freezing ice age temperatures, we see another direct effect, or glaciers known as glacial deposition, which is the settling of sediments left behind by a moving glacier. This process occurs as the melting glaciers drop all of the rocks and sediments they previously picked up. It's almost as if the ice age glaciers were the original litter bugs of the environment, because they spread debris over vast areas. The unsorted materials moved and deposited by a glacier is known as till.
Till can be pushed or deposited into piles. Lines of till that form at the edges of past glaciers leave behind landforms known as moraines. Moraines form in lines and give a general idea of the boundaries and farthest point that the past glacier reached.
We also see drumlins, which are elongated hills composed of glacial till. A number of drumlins can form together in a field, and their unique shape makes them look almost like the backs of whales breaching the surface of the ocean. Glacial erosion and deposition are direct effects of ice age glaciers, but there are also indirect effects that impact the earth.
One indirect effect is the creation of pluvial lakes, which are lakes that were at one time very large due to excessive rainfall associated with glaciation. To recall this term it might help you to understand that the word 'pluvial' means rain in Latin. So pluvial lakes formed due to very heavy rainfall, but there's a catch - pluvial lakes formed in desert areas.
Are you wondering how so much rain fell in the desert? Well, it all had to do with the presence of ice-age glaciers. Glaciers are huge, and during an ice age they can cover about a third of the land. These huge ice cubes changed air flows and weather patterns and turned previously dry areas into wet areas. This allowed basins in these previously dry areas to fill with water, giving us the pluvial lakes. After the ice age, the pluvial lakes began to shrink, but we still see some remaining today, such as the Great Salt Lake in Utah.
Another indirect effect of ice age glaciers is a phenomenon referred to as isostatic depression. This is the sinking of the earth's crust due to pressure from a heavy weight. During an ice age, this heavy weight is the glaciers. Isostatic depression is similar to what happens when you lay down on a mattress and it compresses, or depresses, under your weight. When the glacier eventually melts, the earth's crust rebounds, in the same way your mattress rebounds when you get out of bed in the morning. Of course, your mattress tends to spring back into shape quickly, whereas the rebounding of the earth takes thousands of years. In fact, measurements on the shorelines around the Great Lakes show that this area is still rebounding from the last ice age.
Changes in Sea Level
One other indirect effect that is worth noting is the change in sea level that results with the growing and melting of ice age glaciers. We shouldn't forget that glaciers are frozen water. During the prolonged cold of the ice ages, water that once filled oceans was turned to ice. This resulted in a drop in sea level during the ice ages and the uncovering of large land bridges, such as the bridge that connects Alaska and Siberia. Some ice is still tied up in glaciers today, with modern-day glaciers covering about 10% of the world. If all of these remaining glaciers were to melt tomorrow, the sea level would rise 215 feet, which is more than 21 stories high.
An ice age is a prolonged period of cold with glaciers blanketing much of the earth. These glaciers cause glacial erosion, which is the carving and shaping of the land beneath a moving glacier. Glacial erosion leaves behind glacial horns, with their sharp, angular peaks and cirques that have round hollows with steep sides. Glaciers also carved out millions of lakes and U-shaped valleys. When glaciers melt, we see another process called glacial deposition, which is the settling of sediments left behind by a moving glacier. The unsorted materials moved and deposited by a glacier is known as till. When till accumulates, it can result in moraines, which are lines of till that form at the edges of past glaciers or drumlins, which are elongated hills composed of glacial till.
One indirect effect of ice age glaciers is the creation of pluvial lakes, which are lakes that were at one time very large due to excessive rainfall associated with glaciation. The huge glaciers changed air flows and weather patterns and turned previously dry areas into wet areas, leading to the formation of the lakes.
The glaciers were so heavy that they caused isostatic depression, which is the sinking of the earth's crust due to pressure from a heavy weight. And, they were so massive that they tied up much of the world's water resulting in a change in sea level.
When you are done with this lesson, you should be able to:
- Define ice age, glacier and glacial erosion
- Describe glacial deposition
- Explain what pluvial lakes and isostatic depression are
- Understand how glaciers can affect sea level
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