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Cold Climate - Glaciers and Ice Ages

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1 Cold Climate - Glaciers and Ice Ages

2 Glaciers Glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weight Glaciers form by accumulation and compaction of snow Packed snow becomes firn Then refreezes to ice

3 Formation of Glacial Ice from Snow

4 Glaciation Types Alpine glaciation: found in mountainous regions
Continental glaciation: exists where a large part of a continent is covered by glacial ice Cover vast areas

5 Davidson Glacier near Haines, Alaska An Alpine glacier system

6 Types of Glaciers Alpine Continental

7 Alpine Glaciers Are confined by surrounding mountains Types:
Cirque Glaciers – erode basins in mountainsides Valley Glaciers – flow into preexisting stream valleys Icecaps – form on mountaintops

8 Types of Glaciers– Cirque Glacier
Mount Edith Cavell, Jasper National Park, Canada

9 Types of Glaciers – Valley Glacier
Tongas National Forest, Alaska

10 Types of Glaciers – Icecap and Continental
Sentinal Range, Antarctica Antarctica is the broadest high place on Earth, the ice cap is up to 4km thick and covers the continent Antarctica is a desert, with only 15 cm (6 inches) of snowfall a year around the South Pole The lowest recorded temperature is °C. There is no life in Antarctica except near the coast

11 Types of Glaciers – Piedmont & Tidewater
Piedmont: Originally confined alpine, spread at foot of mountains Source: Jim Wark/Peter Arnold, Inc. Calving

12 Iceberg Calving – Hubbard Glacier, Wrangell-St
Iceberg Calving – Hubbard Glacier, Wrangell-St. Elias National Park, Alaska Releases fresh water to oceans, CO2 to atmosphere. More on this later.

13 A Glacier’s Budget Budget = Gain – Loss
Gains snow in zone of accumulation Loses ice in zone of ablation Budget can be positive (net growth) Static or negative (net melting)

14 A Glacier’s Budget Year round Snow Summer Rain
Note that a glacier is a river. Even if the terminus doesn’t advance, still flows

15 Glacial Flow Internal deformation Basal Sliding
Ice crystals slide past one another Basal Sliding Entire glacier slides downhill on a thin film of meltwater at its base. Glacier always flows toward zone of ablation

16 Mechanics of Glacial Flow

17 Erosion by Glaciers Abrasion Quarrying
Rocks embedded in glacier’s base make linear scratches and grooves in bedrock Quarrying Glacier breaks off and removes large blocks of rock. FROST WEDGING is important

18 Glacial Abrasion in Bedrock
Source: Tom Bean

19 Glacial Erosion – Roche Moutonée

20 Glacial Erosion – Roche Moutonée
Yosemite NP, Calif

21 Erosion by Glaciers (cont.)
Alpine glaciers erode mountain slopes into horseshoe shaped basins called cirques Melting forms cirque lake (tarn) Erosion of two or more cirques erodes intervening rock Horns :pointy peaks made by trios Arêtes: long serrated ridges by pairs Cols: passes through the arêtes

22 Alpine Glacial Erosion

23 Alpine Glacial Erosion
Origin of Hanging Valley

24 Yosemite Falls

25 Valley Glaciers Erode a large quantity of bedrock and sediment
Convert V-shaped stream valleys into U-shaped glacial valleys.

26 U-Shaped Valley in Tracy Wilderness, Southeastern Alaska

27 Seawater Flooded U-Shaped Valleys: Fjords
Bela Bela Fjord, BC When glaciers melt, sea-level rises

28 Erosion by Continental Glaciation
Erosional Landforms much larger in scale than alpine glaciers Whalebacks – huge Roche Moutonée Huge U-shaped troughs – Finger Lakes, Great Lakes, Puget Sound, Loch Ness were all once stream valleys excavated by Ice Sheets

29 Erosion of Preglacial Lowlands (Finger Lakes)

30 Erosion of Lowlands (Great Lakes, Finger Lakes)
Superior Huron Michigan Ontario Erie Source: U.S. Dept. of Interior, USGS Eros Date Center

31 Glacial Deposits - Drift
Collectively called Glacial Drift TYPE 1: UNSORTED Glacial Till: unsorted, unstratified sediments deposited by melting ice. May contain glacial erratics Often accumulates in glacier’s channel and at its terminus as a Moraine: Terminal Moraine: hills of sediment left by a glacier’s retreat. Terminal Moraines may be reshaped by a later glacial advance into Drumlins: rounded elongated hills perpendicular to their original orientation

32 Advance & Retreat: Moraines
Note moraine, retreat or stationary Stationary Analogy: Escalator

33 Stationary & Retreat: Moraine at Terminus

34 Large Granite Erratics

35 Lateral and Medial Moraines

36 Lateral and Medial Moraines – Kennicott Glacier
Wrangell-St. Elias NP, SE AK Lateral and Medial Moraines – Kennicott Glacier

37 Glacier retreats, leaving behind
The Origin of Drumlins Glacier retreats, leaving behind a terminal moraine. Later it advances again, and reshapes the moraine into a drumlin.

38 Drumlins Rochester,NY

39 Glacial Deposits - Drift
TYPE 2: SORTED Outwash: sorted stratified sediments deposited by meltwater streams Loess: wind erosion of drying outwash silt. Eskers: sinuous meltwater deposits of sand and gravel underneath ice

40 Origin of Eskers

41 Eskers in Coteau des Prairies, South Dakota

42 Effects of Glaciation Change Climate – increase precipitation
locally - pluvial lakes Depress continents & lateral rebound Drop sea-level: alter coastlines Form continent-wide Dams Divert streams – Ohio and Missouri rivers

43 Formation of Terraces due to Crustal Rebound

44 Lowered Sea-level - Landbridge

45 Glacier Distribution 20,000 ya
Approximate Maximum

46 Lowered Sea-level exposed continental shelf

47 The Creation of Glacial Lake Missoula
Purcell Lobe blocks Clark Fork River

48 The Draining of Glacial Lake Missoula
Repeated many times, last time kya

49 Giant Ripples of the Missoula Flooding

50 Causes of Ice Ages Plate Tectonics Moves Continents to Poles
Raises mountains above snowline Orbit distance, Axis Tilt and Wobble Moderates solar radiation north of 65 N Milankovitch Cycles ~ 100,000 years Low summertime radiation 65 N, glaciers expand

51 Milankovitch Cycles Discussion: cool summers and wet winters
Moisture content of air masses 100,000 years

52 Warm Wet Winter Cool Summer Cold Dry Winter Hot Summer 41,000 years

53 Discussion: Perihelion and Aphelion
25,700 years

54 One More Point On This The orbital affects that Milankovitch suggested as a partial cause for ice ages each have a different period. They combine at irregular intervals The average is about 100,000 years but that is ONLY an average

55 Earth’s Past Ice Ages (oldest on bottom)
Tertiary- Quaternary cooling – Pleistocene 1.8 mya None in Mesozoic Late Pennsylvanian & Permian Ice covered part “Gondwana” (South Africa, South America, India, Australia, Antarctica) Ordovician glaciation Area that is now the Sahara at South Pole PreCambrian Tillites (Lithified Till) At least three episodes. Interesting examples: 750 mya ice from poles to tropic “SNOWBALL EARTH” Oldest 2.8 bya

56 Permian Glaciation – Gondwana Tillites
Poorly Sorted Unstratified

57 Cenozoic Cooling

58 The Late Tertiary and Quaternary oxygen isotope record measured in marine fossil shells
Evap. water and CO2 during glacial time removes 16O to glacier ice leaving 18O in oceans for CaCO3 shell

59 Pleistocene Glaciation
Since 1.6 mya – more than 30 advances and retreats In 4 large scale pulses. Latest retreat 10,000 years ago Laurentide Little ice age 700 to 150 years ago. Sustained warming since 1850

60 Foraminifera tests - Ice Age
Wisconsinan Illinoian > 30 pulses in 4 or so major groups Kansan Nebraskan Evap. water and CO during glacial removes 16O to glacier ice leaving 18O in oceans for CaCO3 shell warm cold Also spiral direction & diversity dep T

61 Continuous Ice Sheet 20 kya then warming
Scoured 30 M below sea-level

62 Cold pulse from about 1300 to 1850 AD (The so-called “Little Ice Age”) Climate has been warming since then. Discussion: Global Warming Worldwide melting, regardless of cause, releases CO2 and H2O and exposes dark land. The atmosphere receives and holds more heat, and temperature rise. Athabaska Glacier, Columbia Icefield, W. Canada

63 End of Glaciers

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