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Chapter 18 Opening Figure

Mendenhall Glacier

SE Alaska

Glacial till and outwash in Tacoma, west of the NallyValley

Figure 18.36

N Polar view of Earth between 22 – 15 ka showing ice sheets and sea level reduce by ~120 m

Ka = kiloannum = 1000 yr

North American Ice SheetsLast Glacial Period (ca. 20,000 yrs ago)

H-1

Puget Sound Ice

(map D Molenaar, 1987)

Today’s Puget Lowland

Puget Lobe of the Vashon Glacier ~16,000 yr ago

How do we know that we have been in an Ice Age for ~2 Myrs?

Evidence of:1. Glacial Erosion2. Glacial Sediments3. Glacial Landforms

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Climate Since the Cenozoic (65 Ma to today)

Tukwilla Fm

Blakeley FmOhanapecosh Fm

Vashon Fm

Ma = mega annum (1 my)

Glacial Cycles Within an Ice Age

Quaternary Ice Age2 Myrs

Glacial Period

Interglacial Period

1. Glacial ErosionSeattle Area Shows Evidence for 7? Glacial Advances

Drift = any deposit of a glacier

Glacial Sediments in Puget Sound

Interglacial = time between glaciations

Puget Sound During the Ice Age (A Modern Analogy - Columbia Glacier, AK)

Austin Post

3

Dee Molenaar painting

Harry Halverson photoGlacial drift veneer of the Puget Lowland

Cascade Range

Distribution of surficial deposits and extents of Pleistocene glaciers in the vicinity of Mount Rainier (after Crandell and Miller (1974) and Walsh and others,1987) and overlain on 30-meter DEM shaded relief.

Lidar image showing glacial landformsesker

Lidar image showing glacial landforms

esker

drumlins

kettles

Figure 18.1b

4

Figure 18.20b

Braided glacial outwash stream

GLACIER

• A body of ice • Formed on land• Recrystallization of snow• Evidence of movement• Theory of glacial ages

– at present ~10% of land surface glaciated– in past, ~32% of land surface glaciated

GLACIOLOGY

• Distribution of present glaciers– Alpine vs. Continental glaciers– Develop where all of annual snow doesn’t melt

away in warm seasons• Various climates

– Most glacial ice in Antarctica– Glaciers in US

GLACIERS

• Types of Glaciers– Valley glaciers- “ice streams”

• Move down valley

– Ice Sheets & Ice Caps• Flow from high part outward

Figure 18.3a (left)

Ice cap feeding valley glaciers, New Zealand

Fig. 12.10

Antarctica

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GLACIERS

• Growth of glaciers– Snow => Firn => Glacier Ice

• Ablation (Wastage) of glaciers (“shrinkage”)– Melting

• more melting at lower elevations– Evaporation– Calving into Icebergs

• where a glacier flows onto a sea

GLACIER BUDGET

• Positive--Advancing Glacier– Terminus moves forward

• Negative--Receding Glacier– Terminus retreats

• Zone of accumulation– Where some snow remains after the melt season

• Zone of Wastage– Where all snow & some glacier melt

• Equilibrium line– Boundary between two zones

Figure 18.7a Movement of Valley Glaciers

• Gravity driving force• Faster above & in middle of glacier• Basal sliding• Plastic flow

– “flowage”• Internal flowage (plastic flow)• Rigid zone

– Crevasses may form here

Fig. 12.08 EROSION BY GLACIERS

• Under glacier– Polishing and rounding by tools (rocks) in ice

• Roche Moutonnee “Sheep Rocks”• Striations & flutes = scratches & grooves on rock

– Rock flour produced & washed out of glacier• Above glacier

– Frost wedging takes place– Erosion by glaciers steepen slopes– Angular & rugged landscapes created

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Glacial striations, chatter marks, and crescentic gouges upslope of Paradise at Mount Rainier

Fig. 12.12

Figure 18.6a Figure 18.6b

Figure 18.11a Figure 18.11b

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EROSION BY GLACIERS

• Alpine landscapes due to erosion– U-shaped valleys– Hanging valleys– Truncated spurs– Cirques- at heads of valley glaciers– Rock steps

• Rock basin lakes (tarns)

– Horns (saw tooth mountains)– Aretes

Fig. 12.14

Fig. 12.16 Fig. 12.19

DEPOSITION BY GLACIERS

• Till– Unsorted debris

• Erratic• Moraine- body of till

– Lateral Moraine– Medial Moraine- where tributary joins glacier– End moraine-

• Terminal• Recessional

– Ground moraine• Drumlins

DEPOSITION BY MELTED GLACIERS

• Outwash– Stream-deposited sediment

• Sorted sediments

Braided streams typical– Kettles

• Glacial Lakes– (Varves)

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Figure 18.16a

http://www.uwsp.edu/geO/faculty/ritter/images/lithosphere/glacial/till_DDS21_Mt%20Ranier_WA_large.jpg

Figure 18.16b

http://www.ndsu.edu/nd_geology/nd_glacial/images_glacial/outwash_valley_city.jpg

Figure 18.17 Figure 18.21a

Figure 18.21b Figure 18.33d

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Figure 18.33e Figure 18.33f

Figure 18.33g

These visitors along the scenic corridor in 1914 had a closer look at the Nisqually Glacier’s terminus than we do today. This photo by Asahel Curtis shows the terminus just a hundred meters or so upstream of the Nisqually Bridge (the bridgewas rebuilt about 75 m farther downstream after a 1955 washout).

Nisqually Glacier from Ricksecker Point, 1991

Little Ice Age trimline

Little Ice Age lateral

moraine

Nisqually Glacier

terminus

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Effects of Glacial Ages

• 4 major advances during past 2 million years (Pleistocene)– Latest peaked 20,000 years ago– Ended 10,000 years ago

• Direct effects– Scoured much of Canada & New England– Cut Great Lakes– Flattened Midwest– Ice extended into N. America– Alpine ice caps – Cascade Range, Rockies, Sierra, & other

mtns had larger valley glaciers

Effects of Glacial Ages

• Indirect effects– Lowered sea level 400 feet– Wetter climate– Pluvial Lakes

• Some were large lakes in west– Lake Bonneville– Death Valley a lake

– Crustal rebound

Figure 18.40a Figure 18.40b

“Ponding” of the FloodsH-9

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Figure 18.20a Figure 18.22c

Figure 18.23b Figure 18.24a

Ross Ice Shelf

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Figure 18.24b Figure 18.26

Figure 18.27a

Classic U-shaped glacial valley

Figure 18.34a

Moraines of the midwest and Great Lakes area – last Ice Age

Figure 18.35 Figure 18.34b

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Figure 18.36

North Pole view of maximum glacial conditions about 20 ka

Ka = kiloannum = 1000 yr

Figure 18.39a

Loess deposits – wind blown glacial silts. Washington’s Palousealso contains loess.

Figure 18.39b

loess

Figure 18.41a

Figure 18.41b Figure 18.41c

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Figure 18.41d Figure 18.41e

Figure 18.41f Figure 18.42

Pre-glacial (left) and post-glacial (right) drainage systems in North America

Figure 18.43a

(electron photomicrograph)

Figure 18.43b

How stable oxygen isotopes in microfossils record climate

The O18/O16 ratio

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Figure 18.43c

How stable oxygen isotopes in microfossils record climate

The O18/O16 ratio

Figure 18.44

Oxygen Isotope ratio data below; glacial ice data above.

Figure 18.45 Figure 18.46a

Milankovitch cycles—what forces ice ages?

Figure 18.46b

Milankovitch cycles—what forces ice ages?

Figure 18.46c

Milankovitch cycles—what forces ice ages?

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Figure 18.47 Table 18.1