GEOG Jan 30 (L8) Glacial Lakes PDF

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Jan 30 (L8) Glacial Lakes NotesReading Questions: Can you explain what happened to cause the erosion of th eChanneled Scablands and approximately when? What evidence is there for ehte existance of Glacial Lake Missoula and the repeated flood/erosian events? What is catastophism? Why did the findings...

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Jan 30 (L8) Glacial Lakes Notes Reading Questions: - Can you explain what happened to cause the erosion of th eChanneled Scablands and approximately when? - What evidence is there for ehte existance of Glacial Lake Missoula and the repeated flood/erosian events? - What is catastophism? - Why did the findings of Bretz seem to be a rejection of the Principle of Uniformitarianism? - How can the landscape modifications of cataclysmic events be explained through the Principle of Uniformitarianism? - How is the distribution of aquatic life in Cada related to glacial lakes? Paradigm shift by J Harlen Bretz - Had a new explanation and idea but people didn’t want to hear it because they didn’t want to be wrong about what they currently thought - Studied channeled scablands of northwestern USA Channeled scablands: - Ragged, eroded landscape - Holes are 180 feet deep - Cliffs are 340 feet high - These could be explained with a different scale as caused by normal, slow erosion over geologic times - Different scale as in by looking at the depth size, ripples seen in the landscape - Ripples left behind!! Depicted in the picture on the right - Most geologists assumed this scale to be the cause of formation of channeled scablands - Bretz: looked at size, spacing, and placement of different features and said that these are formed by large volumes of water and not just gradual river flow - He also hypothesized that the channels must have been carved over a short period of time perhaps a few days

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This seemed unreasonable to many scientists Many thought he was regressing geology and science back to the period when the Doctrine of Catastrophism was famous - Recall: doctrine static that much of what happened on Earth’s surface was created by catastrophic events Principle of Uniformitarianism - Past geological processes will happen again in the future - This was used to explain scablands - The process occurring in the present is the same as those in the past - Both bound by the same laws of physics Where did the water in the scablakes come from? - Answer: proglacial lakes - This was not obvious to many as it had not previously been studied - Once evidence of proglacial lakes was found, people began to believe Bretz’ theory - IN ICELAND: Jokulhaups (extreme flash floods) - Icelandic people were the first to believe Bretz’ theory because they often saw huge flash floods due to melting of ice - These large flash floods result in extreme amounts of water moving with extreme energy which would then “cut” the landscape as it flowed

Laurentide ice sheet - Eventually, it broke into two pieces: - Cordilleran ice sheet

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Laurentide ice Sheet - At the base of the cordilleran ice sheet, we have the lake Missoula and the channeled scablands Bretz originally conducted his research on

Glacial Lake Missoula - Source for water that eroded the channeled scablands making large creators and depositing sediments - Formed due to rising ground in the sough east and ice sheet in the north with an ice dam somewhere in between - Ice dams are not permanent and can flow with the ice sheet - If they start to flow up, it would lead to a release of tons of water - All the water that under the pressure of the dam would breakthrough - Columbia river acted as a channel to the Glacial Lake Missoula - Studying the Giant Current Ripples helps geologist reconstruct the speed and the depth of the Ice Age floodwater

Varves/Rhythmites - Used to unravel the lake’s history regarding flooding - Sediments deposited during a flood (high flow) - Also, deposited when system would settle and no flow

Where did aquatic life come from? - Rpoglacial lakes form from Laurentide glacial retreat (i.e. great lakes) - Animals moved by shit ballast water or river and streams

Threats? - Glacial Lakes Outburst Floods (GLOFs) threaten the Himalayas - An earthquake or avalanche could trigger a flood - Has happened before in 1994, 29 people died - Could reserve pressure by moving soil to release water...