GEOG Jan 21 (L5) Notes Ice Ages Part 1 PDF

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Summary

Ice Ages Part 1- The evidence on the landReading Questions: - What is a glacier? - Huge ice sheets that cover mountain - Comprised of fallen snow they are compressed into large thickened ice masses - Move like very very slow rivers - Form when snow remains in one location long enough to transform in...

Description

Ice Ages Part 1- The evidence on the land Reading Questions: - What is a glacier? - Huge ice sheets that cover mountain - Comprised of fallen snow they are compressed into large thickened ice masses - Move like very very slow rivers - Form when snow remains in one location long enough to transform into ice - What geographic and climatic conditions are required for glaciers to first form? - When snow remains in the same area year round and accumulates into ice - New layers of snow bury and compress previous layers - What configuration of the continents is prerequisite for an ice age to occur? How has this configuration changed in the past? - Feedbacks occur when substantial portion of the Earth’s land area is located near the poles when snow or ice covers the land surfaces and reflectivity increases. Light is reflected back and allows even more ice to accumulate - Feedback- ice reflects radiation, does not absorb heat, temp drops further, produces more ice coverage and reflects more light and continues on - Why does a glacier move, or “flow”? - Moves under its own massive weight, large force of gravity - Move faster near the top of the glacier because the bottom has more friction as it slides along the ground's surface - Can retreat or advance depending on the amount of snow accumulation or evaporation or melt that occurs - What evidence for past glaciations exists on land (i.e., geomorphic evidence)? Be able to describe these features and know their names. - Glaciers transport material as they move and sculpt the land they move on top of due to their weight and gradual movement - Glacial Erosion - Glaciated valleys - similar to fjords but trough shaped - Fjords- long, narrow coastal valleys carved out by glaciers, “U-shaped”, when the glaciers receded, sea levels rose and covered the floor with sea water - 3 Types of Glacial Erosion - Cirques- note the circular/ bowl shaped pattern

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Aretes - jagged, narrow ridge, where back walls of two glaciers meet and

erode the ridge on both sides

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Horns- created when several cirque glaciers erode a mountain untila all that is left is a steep, pointed peak with sharp, ridge-like aretes leading up to the top

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Glacial Landforms - Terminal Moraines- main sedimentary product of glaciers, basically big dirt piles that accumulate at glacier snouts.

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Eskers - long, rounded ridges of sand and gravel laid down in the beds of streams running beneath glaciers

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Glacial erratics- large boulders conspicuously left behind when the glaciers carrying them melted.

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Drumlins- small, elongated hills of sand and gravel that form underneath large glaciers

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How was some of this geomorphic evidence used to support the Doctrine of Catastrophism? - Erratic boulders→ first thought to have been displaced by the parting of the red sea from the bible, supported the doctrine of catastrophism

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How can geomorphic features or other terrestrial evidence indicates the maximum extent of an ice sheet? - Terminal moraines exist at the furthest extent of an ice sheet How can geomorphic features or their characteristics indicate the direction of its flow? - Striations- can tell you the direction of flow, lines parallel to glacial flow, indicated by long lines What theories have been proposed to explain the advance and retreat of ice sheets? - Incorrect Theories

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- Change in energy output from the sun - Distribution of dust particles in space - Concentration of CO2 in atmosphere - Volcanic eruptions - Vertical movements in earth’s crust - Antarctic ice sheet surge - Ewing donn theory - Stochastic theory Correct Theory - Astronomical Theory→ Croll-Milankovitch Theory

Class Notes- Ice Ages Part 1 -

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Remnants of glaciers exist today Large diversity in biotic environments during the Pleistocene and more species on Earth than found today Geomorphology- study of land - Why does earth look like it does? - What forces shaped the landscape? Case Study: ERRATIC BOULDERS? - Super large boulders just randomly there - First Theory- Flood - Initial explanation- lifted up and deposited in a great flood - Doctrine of catastrophism- early view that history of the Earth to be explained by a series of violent events of catastrophes - Second Theory - Icebergs - Drift theory- boulders frozen in icebergs and deposited in great flood, ice floats - “Flowed” nicely with flood theory - More plausible as it did not require extraordinary forces of water - Third Theory- Glaciers - Erratics moved by glacial ice - Ideas were not readily accepted by those outside Switzerland - The swiss had daily proof - Paradigm shift- moving from flood theory→ icebergs→ glacier theory

Glacial Formations: Terminal Moraine- debris accumulates at the edge of the glacier Drumlins- look like little bumps, tear shaped hills, pointy part of the tear is the bottom of the drumlin, it shows the direction that the glacier advanced Eskers- do not give direction of ice flow, give direction of currents of water in the ice sheet Glacial till- not very fertile, large deposits Loess- very fertile, often found in the prairies USA, central europe, not many large rocks because most will get stuck in glacial till

Early Theories of Pleistocene Glaciations

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What caused the ice sheets to advance and retreat? Based primarily on this geomorphological evidence Evidence - North America: drifts/tills and moraines - Europe: river terraces as well as moraines

Examining River Terraces -

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Gravel beds deposited during cold periods when there was little vegetation THUS greater erosion of the watersheds of the rivers Eroded soil washed into a river system and deposited along banks or in the floodplains when the river overflowed Various levels called terraces Warm perious more vegetation and less erosion thus less sediment This evidence stated four major ice sheets - Assumed 4 ice sheets 4 fold theory of glaciation - 4 flacial stages each associated with ice sheet development and advance - Between these cold glacials there were warm periods called inter-glacials interglacials - interglacials→ when ice retreated -

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Europe 4 river terraces indicated 4 ice sheets - Wurm - Riss - Mindel - Gunz - Each named after a river valley and age determined by depth of erosion North American River Terraces? - Trying to fit the north american evidence into four stages - Wisconsin - Illinoian - Kansan - Nebraskan - Estimated by the weathering of the surface of the “drift” → general term for glacial deposit

What causes climate to change to cause ice sheet advances and retreats? -

Remember: the current theory is that there are 4 ice sheets, so scientists are looking for an explanation to fit this Ice developed at the pole What climate feedback resulted from ice at the poles? - As light is reflected from the ice, you absorb less heat which makes it colder which in turn creates even more ice

What theories have been proposed for ice retreat and advance within the ice house mode? -

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Note: more snow has to accumulate than melts Theory: Change in energy output from the sun Theory: volcanic eruptions - Not enough evidence as major causes Theory: Stochastic Theory - Chaos or random events Theory: variability of CO2 in the atmosphere Theory: Dust in Space - Dust in space can reduce the sun’s energy received by Earth and cause cooling - This could happen if the earth passed through an area of space where dust particles were concentrated - HOWEVER, if more dust fell into the sun it would shine more brightly not less brightly Theory: vertical movements in the earth’s crust - An increase in land evaluation would cause temperatures to drop because higher elevations are colder and more area would be colder - HOWEVER, the progress of mountain building is too slow Theory: Antarctic Ice Sheet Surge Theory: Ewing-Donn Theory

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Terminal Moraine

Drumlins

Eskers

Glacial Till

Loess...