1. Lecture 15 Cold Climates Glaciers and Ice Ages
Glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity
Glaciers form by accumulation and compaction of snow
Packed snow becomes firn
Then refreezes to ice
Davidson Glacier near Haines, Alaska

2. Formation of Glacial Ice from Snow
snowball
iceball
Alpine Glacier: it is just a frozen river

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

4. Alpine Glaciers– Cirque Glacier
Mount Edith Cavell, Jasper National Park, Canada

5. Alpine Glaciers – Valley Glacier
Lateral and medial moraines
Tongas National Forest, Alaska

6. 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 air is too cold to hold much moisture.
The lowest recorded temperature is °C.
There is no life in Antarctica except near the coast

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

9. Iceberg Calving – Hubbard Glacier, Wrangell-St
Iceberg Calving – Hubbard Glacier, Wrangell-St. Elias National Park, Alaska

10. 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)

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

12. Mechanics of Glacial Flow
Internal deformation
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
Basal Sliding Discussion:Ice skates and sleds

13. Erosion 1: Glacial Abrasion in Bedrock
Glaciers cause erosion
Rock embedded in Ice
Source: Tom Bean

14. Glacial Erosion – Roche Moutonée
2. Quarrying
FROST WEDGING

15. Glacial Erosion – Roche Moutonée
Yosemite NP, Calif

16. 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

17. Alpine Glacial Erosion
Cirque and valley glaciers form in river valleys, cut U-shapes

18. Alpine Glacial Erosion
Cirque glaciers erode uphill, widen
Valley glaciers enlarge
Arêtes, Horn, Col, HANGING VALLEYS

19. Yosemite Falls from Hanging Valley

20. U-Shaped Glacial Valley in Southeastern Alaska
Valley glaciers erode a large quantity of bedrock and sediment
Convert V-shaped stream valleys into U-shaped glacial valleys.

21. Seawater Flooded U-Shaped Valleys: Fjords
Bela Bela Fjord, BC
Sea Level rose as glaciers melted

22. 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

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

24. 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 at glacier’s terminus as a Terminal Moraine: hills of sediment left by a glacier’s retreat.
Moraines may be reshaped by a later glacial advance into Drumlins: rounded elongated hills

25. Advance & Retreat: Moraines
Note moraine, no matter direction
Analogy: Escalator

26. Discussion: Advance & Retreat of Glaciers and Terminal Moraines

27. Large Granite Erratics
Favored by climbers with families

28. Medial Moraines

29. Medial Moraines – Kennicott Glacier
Wrangell-St. Elias NP, SE AK
Medial Moraines – Kennicott Glacier

30. The Origin of Drumlins
Glacier retreats, leaving a terminal moraine. Then it advances again, and redistributes the drift as a spoon shaped hill called a drumlin.

31. Drumlins Rochester,NY

32. 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

33. Origin of Eskers

34. Eskers and Kettles in South Dakota

35. Effects of Glaciation Change Climate – increase precipitation
pluvial lakes
Depress continents & lateral rebound
Drop sea-level: alter coastlines
Moraines form Dams – Proglacial Lakes
Divert streams – Ohio and Missouri rivers

36. Formation of Terraces due to Crustal Rebound

37. Lowered Sea-level - Land bridge
Bering
Glacier grows, sea-level drops

38. Lowered Sea-level exposed continental shelf
Massive extinctions of shallow-water marine organisms

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

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

41. Giant Ripples of the Missoula Flooding
Flood kills everything in its path, 26 times
Giant Ripples
Country road for scale

42. Max Glacier Distribution 20,000 ya
Maximum glaciation occurs at coincidence of three astronomical cycles
if high land in polar latitudes

43. Causes of Ice Ages Plate Tectonics Moves Continents to Poles
Raises mountains above snowline
Albedo increases, colder, spread
Orbit distance, Axis Tilt and Wobble
Moderates solar radiation past 65o Latitude
Croll-Milankovitch Cycles ~ every 100,000 years
With many smaller cycles between
Need low summertime radiation past 65o Latitude less melting, glaciers expand

44. Milankovitch Cycles
The energy of solar radiation drops off as the square of the distance
Further away
Not as hot
100,000 years

45. High latitude getting more sunlight in winter
Warm Wet Winter
Cool Summer
Snow doesn’t melt
Glaciers grow
High latitude getting less sunlight in summer
Cold Dry Winter Hot Summer
Snow melts
Glaciers shrink
High latitude getting more sunlight in summer
41,000 years

47. at Perihelion
at Perihelion
Determines which hemisphere gets conditions suitable for glaciation
25,700 years

48. 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
Many glaciation peaks are about 100,000 years apart, but that is ONLY an average. This suggests that orbital ellipticity is important. The worst glaciations occur when minimum tilt coincides with maximum ellipticity.

49. Earth’s Past Ice Ages Tertiary to Quaternary cooling – Pleistocene
None in Mesozoic
Late Pennsylvanian & Permian
in southern continents (Gondwana)
Ordovician glaciation (Gondwana)
Area that is now the Sahara at South Pole
PreCambrian Tillites (Lithified Till)
Three, maybe four,episodes
Oldest 2.8 bya
750 mya ice from poles to tropic “Snowball Earth”
Cenozoic
Mesozoic
Paleozoic
PreCambrian

50. Permian Glaciation – Gondwana Tillites

51. Cenozoic Cooling
Southern Ocean forms
Central America Forms

52. Foraminifera tests - Ice Age
Warm
Cold
Wisconsinan
Illinoian
About 30 pulses in 4 or so major groups
Kansan
Nebraskan
3. Also spiral direction & diversity depends on Temp.
1. Evap. water and CO2
removes 16O from oceans
18O left in oceans
used to make shells
2. Ice traps CO2 and water with light oxygen

53. Continuous Ice Sheet 20 kya
Scoured 30 M below sea-level

54. Global Temperatures Cycle, largest 100,000 Year (orbit eccentricity)
Smaller signals about 25K and K
Interglacials get really WARM

55. The Holocene Latest retreat began 10,000 years ago
The Holocene
Latest retreat began 10,000 years ago
Climate varied. Hot 8000 – 4000 ya
Medievil Warm: 800 – 1200 AD
Little ice age AD until 1850
Widespread Famine
1253 Pueblo cliff-dwellings abandoned.
1340s AD Black Death Bubonic Plague

56. Holocene Temperature Variations
Mann’s Hockey Stick +1
2004
Water
freezes -1
Thousands of Years BP

57. Sustained warming since 1850
Athabaska Glacier, Columbia Icefield, W. Canada
2005 Greenland glacier retreated 9 miles!
Antarctic Glaciers started melting this season