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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Harry Williams, Geomorphology 1LEGACY OF THE QUATERNARYThe Quaternary Period is divided into 2 epochs - the Pleistocene (1.8* mybp - 10,000 ybp) and the Holocene (10,000 ybp - present). The Pleistocene was a time of fluctuating colder climates that resulted in a number of extensive glaciations or ICE AGES (* frequently revised).Harry Williams, Geomorphology 2At present, ice covers about 10% of the land surface, whereas at its maximum extent during the Pleistocene it covered about 30%. Ice cover in the northern hemisphere about 15,000 years ago.Harry Williams, Geomorphology 3In the study of landforms, Pleistocene glaciation is important since many areas glaciated in the Pleistocene are still dominated by glacial landforms today, even 10,000 years after the last Ice Age ended. The reason for this is that glaciers are capable of massive erosion and deposition and leave a long-lasting imprint on the local geomorphology. If you visit the northern states, or other glaciated regions, the only way to understand the local geomorphology is to recognize that these are glacial landscapes formed by ice that is no longer present.Harry Williams, Geomorphology 4In North America, two distinct types of glaciation occurred:ALPINE GLACIATION, characterized by valley glaciers, in mountainous areas of the western U.S.; and CONTINENTAL GLACIATION, characterized by large unconfined ice sheets, over much of Canada and the northern states.ALPINE GLACIATION CONTINENTAL GLACIATIONHarry Williams, Geomorphology 5Landforms of Alpine GlaciationEROSION is the dominant process in glaciated mountainous regions. The glaciers are confined to pre-existing steep valleys and tend to erode vertically. Wide U-shaped glacial troughs, hanging valleys, horns, cirques, aretes and truncated spurs are the result.B. GlaciatedHarry Williams, Geomorphology 6mountainshillscliffs ridgesTruncated SpurHarry Williams, Geomorphology 7Examples from North America.Cirque, Labrador, Canada.Harry Williams, Geomorphology 8Tarn - lake formed in the bottom of a cirque (view down valley).Harry Williams, Geomorphology 9Hanging valleys.Harry Williams, Geomorphology 10Horns, aretes, cirques.Harry Williams, Geomorphology 11Glacial trough, hanging valley.Harry Williams, Geomorphology 12Fjord - a submerged glacial trough - common on the coast of B.C., Alaska.Harry Williams, Geomorphology 13Landforms of Continental Glaciation.What causes Ice Ages? Changes in the shape of the earth’s orbit, the tilt of earth’s axis and the direction of tilt all exhibit cyclic change. Milankovitch theory describes the collective effects of these changes, which combine to cause cold climates about every 100,000 years.Harry Williams, Geomorphology 14Extent of glacial deposits (“Drift”) from Pleistocene glaciations in the northern midwest. The last large glaciation was the Wisconsin. The Illinoian is an older glaciation that extended further south.Harry Williams, Geomorphology 15DEPOSITION is dominant in lowland areas at the margins of continental glaciers - the northern states in North America. This is where debris carried in the ice is released as the ice melts. Further back from the ice front, (mainly in Canada) erosion can occur by SCOURING of the surface by debris (rocks) carried at the base of the ice. General scouring of the surface removed much topsoil from these areas, which is slow to recover due to the cold climates. Scouring also creates small grooves or striations or lager troughs aligned with the direction of ice flow; many larger troughs filled with water to become lakes.Harry Williams, Geomorphology 16Harry Williams, Geomorphology 17Canada Shield lakes.Harry Williams, Geomorphology 18Glacial striations.Harry Williams, Geomorphology 19Much of the landscape of the northern mid-west is dominated by depositional landforms. Deposition can occur directly from the ice - erratics, ground moraine, drumlins, end moraines - or from meltwater (mainly gravel, sand, mud) in the form of lake deposits, outwash (melt-water stream) deposits and eskers (sub-glacial melt-water stream deposits). Outwash and esker deposits have a similar character to alluvial depositsHarry Williams, Geomorphology 20Ice-marginal areasHarry Williams, Geomorphology 21Bouldery ground moraine, Canada. This debris is “plastered” onto the surface directly under the ice near the margins of the ice sheet.Harry Williams, Geomorphology 22Areas of ground moraine usually are not great for farming (boulders, water-logging, hummocky). They can be used for dairy farming e.g. Wisconsin. Hence all the cheese.Harry Williams, Geomorphology 23Erratics are common in ground moraine regions (this one is in Manitoba above the tree line). Erratics provide a clue to the source of ice and ice movement.Harry Williams, Geomorphology 24Drumlin, Alberta. Drumlins are formed from moraine that is pushed up into a hill by over-riding ice and then “streamlined” by the ice flow. They “point” in the direction of former ice flow.Ice flowHarry Williams, Geomorphology 25Drumlins, Manitoba.Harry Williams, Geomorphology 26End moraine forming on Baffin Island, today. Debris carried by the ice piles up at the front of the ice sheet (where melting occurs).Harry Williams, Geomorphology 27Road cut through Pleistocene end moraine, Quebec. Moraines are always mixtures of different sized sediment.Harry Williams, Geomorphology 28Esker - Manitoba. These are ridges of meltwater deposits laid down in a tunnel under the ice. The sediment is usually well-sorted sand and gravel.Harry Williams, Geomorphology 29Esker, Quebec.Harry Williams, Geomorphology 30Outwash is sand and gravel deposited by meltwater streams that form in the summer. These streams are typically braided and create wide outwash plains. Outwash can extend 10’s of miles beyond the margin of an ice sheet. Outwash sediment has the character of alluvium (well-sorted, stratified).Harry Williams, Geomorphology 31Outwash plains are great for farming. They are flat, well-drained and fertile. This one is in Quebec.Outwash plainBedrock ridgeHarry Williams, Geomorphology 32Outwash plain, Skagit Valley, Washington State.Harry Williams, Geomorphology 33Summary: glaciers and ice sheets cause massive erosion and deposition.


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UNT GEOG 3350 - glacial

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