Presentation on theme: "The Illustrated History of GLACIAL EROSION www.regentsearth.com/Powerpoints/Tutorials/Glaciers.ppt."— Presentation transcript:
The Illustrated History of GLACIAL EROSION
This is a glacier. Actually its several glaciers coming together to form a larger one. The glaciers are hundreds of feet thick. They have enormous mass. They flow downhill due to the FORCE OF GRAVITY. These are VALLEY or ALPINE glaciers. They flow in valleys between mountains. They are small when compared with CONTINENTAL glaciers which cover entire continents. Antarctica is covered by a continental ice sheet. The dark bands in the glacier are rocks ripped from the sides of the mountains as the glaciers flow. The dark bands are called MORAINES. The rock will be carried to the point where the glacier melts and then it will be deposited. A glacier is a rock conveyor belt.
Heres another view of a glacier showing the Terminal Moraine. It forms at the point at which the rate of melting is equal to the flow of ice. You can also see a Medial Moraine in the middle of the glacier.
The V-shaped valley seen to the right is typical of stream or water erosion. As the stream flows, its cutting tools which are the rocks and stones it carries, cut deeper and deeper into the streambed forming a V-shape. If the climate gets colder and the valley fills with ice the glacier will rip rocks from the sides as well as the bottom of the valley. This will widen the valley and change its shape. To the left is a wide U-shaped valley which is typical of glacial erosion. V-shaped = streams U-shaped = glaciers
Another view of a typical U-shaped glacial valley. And another
The power of glaciers can be seen in this photo of 'El Capitan' aka Half Dome mountain in Yosemite Valley in California. As glaciers moved through this valley they sliced this solid granite mountain in two and scooped out the U-shaped valley to the left.
As glaciers flow, the rocks embedded in the ice cut deep PARALLEL GROOVES in the bedrock beneath. When the glaciers melt these parallel grooves remain as evidence that the glaciers were there. The picture to the right shows bedrock exposed at the Bronx Zoo. Above more parallel grooves and scratches in exposed bedrock.
Sometimes the grooves are very deep and dramatic such as these from the Peruvian Andes (left) or these (right) known as Kelleys Grooves found on Kelleys Island, Ohio.
These rocks were embedded in the ice at the bottom of a glacier. As the glacier moved over bedrock it was rocks like these that cut the parallel grooves. In the process these rocks tumbled and rolled becoming SCRATCHED and POLISHED. SCRATCHED and POLISHED boulders are evidence of glacial erosion.
Unlike streams or rivers glaciers can carry enormous blocks of stone for many, miles. When the glaciers melt these rock are left stranded far from their origins. Such rocks are called ERRATICS. An erratic is a boulder that was transported to its present location and is generally unrelated to the underlying bedrock. The ERRATIC on the left was deposited in Central Park.
Some erratics come to rest in strange places. Some are deposited closer to home like this boulder in Eastport.
This is a satellite view of the Finger Lakes region of New York State. The finger lakes are very deep and narrow parallel lakes scooped out during the last ices age. The glaciers movement from north to south accounts for the N-S orientation of these bodies of water. Lakes like these are found all over the world wherever the last continental ice sheet scraped and scarred the land.
If the U-shaped depression carved by the glaciers reaches all the way to the sea it is often referred to as a fjord. A fjord is a long, narrow salt water bay carved by glaciers and they are found in many countries all over the world. The photo was taken at Misty Fjords in Alaska.
The material transported by a glacier is called TILL. When the glacier melts the till is deposited in a pile. There is no sorting as occurs when a stream slows. UNSORTED SEDIMENT is good evidence of glacial deposition. Above and to the right are pictures of unsorted glacial till. Material from fine silt to large boulders are mixed together randomly. Long Island is composed completely of glacial material.
Sometimes the glacial till is deposited in mounds or hills. These are called DRUMLINS. The drumlins above are found in Scotland but similar features are found all over the northern hemisphere. Often drumlins are so large that they cannot be appreciated for what they are except when photographed from high altitudes.
A drumlin in the midwest.
As glaciers retreat (melt) huge blocks of ice may remain buried in the earth. As these blocks gradually melt they leave deep depressions which fill in with water forming "KETTLE LAKES" such as those seen above. Kettle lakes represent more evidence that a region has undergone glaciation.
A summary of glacial features 1) U-shaped valleys 2) Parallel grooves in bedrock 3) Scratched and polished boulders 4) Erratics 5) Long, deep, glacial lakes 6) Unsorted sediments 7) Drumlins 8) Kettle lakes
Glaciers are an endangered species. This is the Muir glacier in Glacier Bay, Alaska photographed in 2007.
The Muir Glacier is retreating rapidly. Ice is melting faster than new ice can replace it. The arrows show where the glacier was just a few years ago. As it melts it exposes rock that appears lighter because it hasnt had time to weather.
These views show how the Muir Glacier has changed in just over half a century. In that time it has retreated over 20 km and it continues to get smaller every year. People may debate the causes of global warming but the evidence is clear. The Earth IS warming.
This is the Mendenhall Glacier in Juno, Alaska. The picture was taken in If these people had been standing here in 1987 they would have been under 65 feet of ice.
Lastly, a very quick review of essential terms What kind of sediments do glaciers produce? UNSORTED What kind of valleys are associated with glaciers? U-SHAPED What term applies to a boulder deposited by a glacier? ERRATIC What do glaciers do to the rocks they pass over? They cut LONG,PARALLEL GROOVES What evidence indicates that a rock was transported by a glacier? It may be SCRATCHED and POLISHED