Lecture 15 Cold Climates Glaciers and Ice Ages http://www.aad.gov.au/asset/webcams/mawson/ 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

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

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

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

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

Types of Glaciers – Icecap and Continental http://www.nmm.ac.uk/server/show/conWebDoc.1221 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 -89.2 °C. There is no life in Antarctica except near the coast

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

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

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)

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

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

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

Glacial Erosion – Roche Moutonée 2. Quarrying FROST WEDGING

Glacial Erosion – Roche Moutonée Yosemite NP, Calif

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

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

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

Yosemite Falls from Hanging Valley

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.

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

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

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

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

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

Discussion: Advance & Retreat of Glaciers and Terminal Moraines

Large Granite Erratics Favored by climbers with families

Medial Moraines

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

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.

Drumlins Rochester,NY

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

Origin of Eskers

Eskers and Kettles in South Dakota

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

Formation of Terraces due to Crustal Rebound

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

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

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

The Draining of Glacial Lake Missoula Repeated many times, last time 13000 kya

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

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

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

Milankovitch Cycles http://en.wikipedia.org/wiki/Milankovitch_cycles The energy of solar radiation drops off as the square of the distance Further away Not as hot 100,000 years

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

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

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.

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

Permian Glaciation – Gondwana Tillites

Cenozoic Cooling Southern Ocean forms Central America Forms

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

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

Global Temperatures Cycle, largest 100,000 Year (orbit eccentricity) Smaller signals about 25K and 41K Interglacials get really WARM

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

Holocene Temperature Variations Mann’s Hockey Stick +1 2004 Water freezes -1 12 6 0 Thousands of Years BP http://en.wikipedia.org/wiki/Image:Holocene_Temperature_Variations.png

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