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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 14 Glacial Landforms and the Ice Age Visualizing Physical Geography.

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Presentation on theme: "Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 14 Glacial Landforms and the Ice Age Visualizing Physical Geography."— Presentation transcript:

1 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 14 Glacial Landforms and the Ice Age Visualizing Physical Geography by Alan Strahler and Zeeya Merali

2 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter Overview Glaciers Alpine Glaciers Ice Sheets and Sea Ice The Ice Age

3 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Glaciers Glacier: large natural accumulation of land ice affected by present or past flowage Glacial ice has shaped many landforms in middle and high latitudes Glacial ice sheets affect global climate Glaciers reflect sunlight Glacial ice affects global heat transport Volume of glacial ice affects sea levels Large bodies of ice are plastic because of pressure on ice at bottom of mass Large body of ice can flow in response to gravity Ice on a slope can slide downwards Ice sheet: large thick plate of glacial ice moving outward in all directions

4 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Glaciers Glacial ice builds up when snowfall in winter exceeds snow melted in summer Each annual layer of snow, melts, refreezes, forms ice Weight of ice compresses the lower layers into hard crystalline ice When the ice mass becomes thick enough, the lower layers flow plastically Glacial ice forms where temperatures are low and snowfall is high Alpine glacier: long, narrow mountain glacier occupying the floor of a trough-like valley

5 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Glaciers Glaciers contain rock of all sizes Glaciers and ice sheets erode and deposit great quantities of sediment Glacial abrasion: rock fragments in a glacier scrape and grind the bedrock Plucking: moving ice plucks loosened rock material and carries it away Sediment is carried, then deposited when the ice melts

6 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Alpine Glaciers Upper part of the glacier is brittle Lower part is plastic Zone of accumulation: glacier is growing Zone of ablation: glacier is evaporating/melting Alpine glacier can slide downhill on meltwater and mud Rate of movement: few centimeters/day to several meters/day Surge: rapid movement of alpine glacier, up to 60 m/day for several months

7 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Alpine Glaciers Landforms Made by Alpine Glaciers

8 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Alpine Glaciers Landforms Made by Alpine Glaciers

9 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Alpine Glaciers Landforms Made by Alpine Glaciers Cirque: valley head enlarged and hollowed out by glaciers, producing bowl-shaped valley Arête: sharp ridge formed between two cirques Horn: steep-sided peak formed by glacial erosion from three sides Col: natural pass or low notch in an arête between opposed cirques Moraine: accumulation of rock debris carried by an alpine glacier and deposited by the ice to become a depositional landform Tarn: small lake occupying a rock basin in a cirque Hanging valley: stream valley that has been truncated by glacial erosion so as to appear in cross section in the upper wall of a glacial trough

10 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Alpine Glaciers Landforms Made by Alpine Glaciers

11 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Alpine Glaciers Landforms Made by Alpine Glaciers Glacial trough: deep, steep- sided rock trench formed by alpine glacier erosion Fiord: narrow, deep ocean inlet partially filling a glacial trough

12 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Ice Sheets of the Present Antarctic Ice Sheet 13 million sq km 4000 m thick Greenland Ice Sheet 1.7 million sq km 3000 m thick

13 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Sea Ice and Icebergs Sea Ice: floating ice of the oceans formed by direct freezing of ocean water Always <5 m thick Pack ice: sea ice that completely covers the sea surface Ice floes: individual patches of sea ice Upper part fresh water; lower part salty

14 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Sea Ice and Icebergs Iceberg: mass of glacial ice floating in the ocean that has broken off a glacier that extends into tidal water May be hundreds of meters thick About 5/6 of the iceberg is submerged Always fresh water

15 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Landforms Made by Ice Sheets Ice sheets scrape off regolith and abrade bedrock Grooves, scratches, and polished rock show evidence of ice sheets

16 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Landforms Made by Ice Sheets Ice sheets pick up rock fragments, transport them, and deposit them when the ice evaporates or melts Glacial drift: general term for all varieties and forms of rock debris deposited by ice sheets Stratified drift: layers of sorted clays, silts, sands or gravels, deposited by meltwater streams or lakes Till: unstratified mixture of rock fragments of all sizes, deposited directly by the ice Ground moraine: thin, even cover of till

17 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Esker: narrow, often sinuous embankment of coarse gravel and boulders deposited in the bed of a meltwater stream in a tunnel within stagnant ice in an ice sheet Drumlin: smoothly rounded, oval hills of glacial till, formed by the moving ice Terminal Moraine: glacial till that accumulates at the farthest advance of the ice sheet

18 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Landforms Made by Ice Sheets Moraine: accumulation of rock debris carried by an ice sheet and deposited by ice to become a depositional landform Outwash Plain: formed from stratified drift left by streams issuing from the ice

19 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Landforms Made by Ice Sheets Recessional Moraine: moraine formed when the ice paused in its retreat Kame: steep-sided mound of stratified sand and gravel deposited at or near the terminus of a glacier

20 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Sea Ice Landforms Made by Ice Sheets Pluvial Lakes: lakes formed during a moister climate, during the ice ages Many pluvial lakes formed in the western U.S. Lake Bonneville, in western Utah, was about the size of Lake Michigan Pluvial lakes shrank or dried up as the climate became warmer and drier

21 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Ice Age Glaciation: single episode or time period in which ice sheets formed, spread, and disappeared Glaciation occurs when temperatures drop or snowfall increases There have been many glaciation episodes in Earth’s history 55 million years ago 5 million years ago Recent ice ages

22 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Ice Age Late-Cenozoic Ice Age: series of glaciations, deglaciations, and interglaciations experienced during the late Cenozoic Era Maximum Glaciation in North America and Europe

23 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Ice Age Investigating the Ice Age Scientists study the glacial history of the Ice Age: Take sediment core samples on the deep ocean floor Use evidence of magnetic reversals to find the age of the sediments Study composition and chemistry of the cores Create a record of dates, temperatures, biology, and chemistry using the core samples Deep-sea cores show alternating glaciations and interglaciations going back 2-3 million years

24 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Ice Age Possible Causes of the Ice Age 1.Motions of tectonic plates brought land- mass to high latitudes 2.Volcanic activity produced dust that blocks solar radiation 3.Decrease in Sun’s energy output 4.Change in atmospheric composition; reduction in greenhouse gases

25 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Ice Age Possible Causes of Glaciation Cycles Astronomical hypothesis: explanation for glaciations and interglaciations based on cyclic variations in the solar energy received at the Earth’s surface

26 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Ice Age Holocene Environments Holocene Epoch: last epoch of geologic time, commencing about 10,000 years ago and including the present Three major climate periods in Holocene: Boreal Stage: boreal forest vegetation in midlatitude regions Atlantic Stage: warmer temperatures, about 8000 years ago Subboreal Stage: cooler, about 5000 years ago to 2000 years ago During past 2000 years: Warm from AD 1000 to 1200 Little Ice Age from AD 1450 to 1850 Global temperatures increasing at present Fossil pollen and spores preserved in glacial bogs show changes in vegetation over time

27 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Global Warming Disintegration of Larsen B ice shelf, Antarctica, Jan Feb Mar Mar 2002

28 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ice Sheets and Global Warming Polar sea ice has been decreasing in the last 50 years


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