The Illustrated History ofGLACIAL EROSION
This is a glacier. Actuallyits several glaciers comingtogether to form a larger one.The glaciers are hundreds offeet thick. They have enormousmass. They flow downhill dueto the FORCE OF GRAVITY.These are VALLEY or ALPINEglaciers. They flow in valleysbetween mountains. They aresmall when compared withCONTINENTAL glaciers whichcover entire continents. Antarctica is covered by a continental ice sheet.The dark bands in the glacier are rocksripped from the sides of the mountains asthe glaciers flow. The dark bands are calledMORAINES. The rock will be carried to thepoint where the glacier melts and then it willbe deposited.
A glacier is a rock conveyor belt.
Heres another view of a glacier showing the Terminal Moraine. It formsat the point at which the rate of melting is equal to the flow of ice. Youcan also see a Medial Moraine in the middle of the glacier.
The V-shaped valley seen to theright is typical of stream or watererosion. As the stream flows, itscutting tools which are the rocksand stones it carries, cut deeperand deeper into the streambedforming a V-shape.
If the climate gets colder and thevalley fills with ice the glacier willrip rocks from the sides as well asthe bottom of the valley. This willwiden the valley and change itsshape.To the left is a wideU-shaped valley whichis typical of glacial erosion.V-shaped = streamsU-shaped = glaciers
Another view of a typicalU-shaped glacial valley.And another...........................
The power of glaciers can be seen in this photo of 'El Capitan' aka Half Domemountain in Yosemite Valley in California. As glaciers moved through thisvalley they sliced this solid granite mountain in two and scooped out theU-shaped valley to the left.
As glaciers flow, the rocks embeddedin the ice cut deep PARALLEL GROOVESin the bedrock beneath. When the glaciersmelt these parallel grooves remain asevidence that the glaciers were there.
The picture to the right shows bedrockexposed at the Bronx Zoo.Above more parallel grooves andscratches in exposed bedrock.
Sometimes the grooves arevery deep and dramatic such as these from the PeruvianAndes (left).........
or these (right) known as KelleysGrooves found on Kelleys Island,Ohio.
These rocks were embedded in the iceat the bottom of a glacier. As the glaciermoved over bedrock it was rocks likethese that cut the parallel grooves. Inthe process these rocks tumbled androlled becoming SCRATCHED andPOLISHED.SCRATCHED and POLISHEDboulders are evidence of glacialerosion.
Unlike streams or riversglaciers can carry enormousblocks of stone for many,miles. When the glaciersmelt these rock are leftstranded far from theirorigins. Such rocks are called ERRATICS. An erratic is aboulder that was transportedto its present location and isgenerally unrelated to theunderlying bedrock.The ERRATIC on the left was depositedin Central Park.
Some erratics come to restin strange places. Some are deposited closer to homelike this boulder in Eastport.
This is a satellite viewof the Finger Lakesregion of New York State.The finger lakes are verydeep and narrow parallellakes scooped out duringthe last ices age.The glaciers movementfrom north to south accounts for the N-S orientation of thesebodies of water.
Lakes like these are foundall over the world whereverthe last continental icesheet scraped andscarred the land.
If the U-shaped depressioncarved 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 iscalled TILL. When the glacier melts thetill is deposited in a pile. There is nosorting as occurs when a stream slows.UNSORTED SEDIMENTS is good evidenceof glacial deposition.Above and to the right arepictures of unsorted glacialtill. Material from fine silt to large boulders are mixed together randomly.
You live on unsorted glacialtill since 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 features1) U-shaped valleys2) Parallel grooves in bedrock3) Scratched and polished boulders4) Erratics5) Long, deep, glacial lakes6) Unsorted sediments7) Drumlins8) Kettle lakesLearn these terms. Whenever you see one on a test oron the regents the answer is always "GLACIERS".
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 fasterthan new ice can replace it. The arrows show where the glacier was just a few years ago. As it melts it exposesrock that appears lighter because it hasnt had time toweather.
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 2007. 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 that arelikely to appear on the regents..............What kind of sediments do glaciers produce? UNSORTEDWhat kind of valleys are associated with glaciers?U-SHAPEDWhat term applies to a boulder deposited by a glacier?ERRATICWhat do glaciers do to the rocks they pass over?They cut LONG,PARALLEL GROOVESWhat evidence indicates that a rock was transported bya glacier?It may be SCRATCHED and POLISHED