ESS 203 -Glaciers and Global Change · On a rocky bed: •Higher water pressure "floats" ice. •Higher pressure reduces friction with the bedrock. •If bed is "rough", high pressure

ESS 203 - Glaciers and Global Change

Outline for today• Volunteer for today’s highlights on Friday: ________• Summary of last Wednesday’s class – Lauren Fernandez

• Sliding, fracture• Glacial World

Lab next week• Glacial landforms

Wednesday January 29, 2020

Mid-term #1It will be in one week - on Wednesday February 5.• 6 study questions are posted; 3 of these will form the

actual test.• Be sure to read the notes on the TESTS page “Writing a

test”

Study sessions?• Friday Jan 31 11:30 – 1:30 JHN 011• Monday Feb 3 10:30 – 1:30 JHN 011• Tuesday Feb 4 1:30 – 4:30 JHN 027

ESS 203 - Glaciers and Global Change

Writing assignment due FridayNow is a good time to decide which question(s) you

will try first, and share with peers informally or at discussion sessions …

• Write out your current best answer to one Quiz study question that you will take to a study session.

• I won’t assign a grade to your preliminary answer. But it’s a C/NC contribution to class participation.

• It’s for your own good. Trust me. J

Get the data directly from World Glacier Monitoring Service

https://wgms.ch/latest-glacier-mass-balance-data/

Are the glaciers growing or shrinking?

https://wgms.ch/latest-glacier-mass-balance-data/

For more than a century, the World Glacier Monitoring Service (WGMS) and its predecessor organizations have been compiling and disseminating standardized data on glacier fluctuations. Thereto, the WGMS annually collects glacier data through its scientific collaboration network that is active in more than 30 countries. In close collaboration with the U.S. National Snow and Ice Data Center (NSIDC) and the Global Land Ice Measurements from Space (GLIMS) initiative, the WGMS runs the Global Terrestrial Network for Glaciers (GTN-G) in support of the United Nations Framework Convention on Climate Change (UNFCCC).

Regelation (“refreezing” in French)

thescienceclassroom.wikispaces.org

www.studyblue.com

• Glacier sliding past small bumps

Sliding SpeedSliding speed of glaciers increases if• Ice thickness increases• Ice surface slope increases• Water pressure at the bed increases

Recall demo: less force needed to make a block slide as water pressure under it increases

On a rocky bed:• Higher water pressure "floats" ice.• Higher pressure reduces friction with the bedrock.• If bed is "rough", high pressure also reduces contact

area where sliding friction can occur.

Sliding Speed and Basal Water Pressure

On a "soft" bed:• High water pressure softens basal mud.• Softer mud deforms and flows faster. • Carries glacier along with it faster.

Hard bed rock

Ice Water in cavities

Where When Sliding DeformationSpeed Speed (surface)

Nisqually Glacier Summer/fall 70 m a –1 15 m a –1

Mt RainierNisqually Glacier Winter/spring 35 m a –1 20 m a -1Blue Glacier summer 10 m a –1 40 m a –1

(lower reach)Variegated Glacier Surging 10,000 m a –1 40 m a -1Jakobshavn Isbrae All the time 8-12 km a-1 5 km a –1

(Greenland)Ice Stream Whillans All the time 500 m a –1 5 m a –1

(West Antarctica)

Examples of Sliding Speeds

When a glacier changes its motion quickly (e.g. daily or weekly), the cause must be a change in the sliding speed.

• The internal deformation (quasi-viscous flow) cannot be radically altered until the thickness, or slope, or temperature of the glacier change significantly.

• All of these take a much longer time to change.

Rapid Changes in Speed

Why does Water Pressure Change?

Variations in water level cause changes in basal water pressure.

Height of water in water tower controls water pressure in faucets.

Origin of water• Melting of ice and snow at the surface • Rain • Frictional melting from ice sliding over bedrock.

Result• Large supply of water on hot summer days and

after rain storms.

Water Flow in Glaciers

Rivers on the Greenland Ice SheetVibeke Gletscher, East Greenland

An opportunity to go rafting?

Probably not a good idea…

Hambrey and Alean, Glaciers.~300 m

Streams on Glaciers

Water can melt channels into glacier ice.

• Water has lower albedo (darker) than ice, so water absorbs more sunlight than ice does.

• Water dissipates potential energy as it loses elevation.

• Water in contact with ice stays at 0oC.

• So what happens to that energy?

Austre Lovenbreen, Spitsbergen. Hambrey and Alean. Glaciers.

Moulins

Water will find a way somehow to move down into a glacier.• a supraglacial stream will typically flow into a crevasse.

Mer de Glace, FranceHambrey and Alean. Glaciers.

We can see the water coming out at a glacier terminus• But where has it been?

Tunnels

Fox Glacier, NZ.Hambrey and Alean. Glaciers.

Schematic of Hydraulic System

Linked CavitiesIn absence of subglacial tunnels, water flows through a linked-cavity system of interconnected basal cavities and narrow passage-ways.

• Drainage is inefficient.• High water pressure is needed to carry even limited amounts of water.

• Water will collect in crevasses and cavities until high pressures are reached.

(Hooke, Fundamentals of Glacier Mechanics)

Map

Vertical section

Linked Cavities in Central Park

(http://www.swisseduc.ch/glaciers/)

Glaciated bedrock with ledges, cracks, and hollows

TunnelsArborescent networks of tunnels can carry large volumes

of water at relatively low pressure compared to the pressure due to the weight of the overlying ice.

• Water flows from high pressure to low pressure.• Water will flow from linked cavities into tunnels.Ice also flows from high

to low pressure.• Ice also flows into the

tunnels. • Energy dissipated by the

flowing water melts off the walls as fast as they can close in.

Early winter: little melt-water, low water pressure. • Tunnels close, linked cavities survive.Late winter: seepage, basal melt.• water pressure rises slowly, sliding increases slowly.Spring: high melt-water flux enters linked cavities.• Water pressure rises, sliding increases slowly.Early summer: too much water overloads cavities.• Sliding hits its peak.• Surface rises, cavities join, tunnels start to form.Late summer: water flows in low-pressure tunnels.• Basal water drains, sliding slows down.

Seasonal Water Cycle

Flow of Nisqually Glacier

Nisqually River comes from under the glacier.

20

10

m/yr

m/yr100

50

75

54

3210

m3/sec

Surface speed• Measured

Speed due to viscous flow (deforming ice).

• Calculated from ice thickness and slope.

Sliding speed• Calculated as their

difference.

(Hodge, S., 1974. J.Glaciol.)

Brittle Behavior in GlaciersCrevasses can form in the upper "skin" (about 30

meters, or 100 ft) of flowing glacier ice, when the ice tries to stretch rapidly.

Hambrey and Alean, 2005. Glaciers.

• At greater depths, the ice continually flows back in to close up the cracks.

• Crevasses almost always form at right angles to the direction of the maximum stretching.

Demo: silly putty

HELP!COFFEE*

Hawley Extremely LightweightPortable !Crevasse Orientation Freehand Failure Estimation Equipment

[*Designed by former ESS 203 TA Bob Hawley]

Where Crevasses tend to Form

Crevasse on Griesgletscher Switzerland

Hambrey and Alean, 2005. Glaciers.

• How might this crevasse have formed?

• Since this is summer, you can see it easily.

• In winter it might be hidden by a thin snow bridge (falling through is bad for your health!).

Crevasses on Fox Glacier, New Zealand

2006 ©Glaciers online · J. Alean · M. Hambrey

• How did these crevasses form?

Crevasses on Arctic Piedmont Glaciers

http://www.swisseduc.ch/glaciers/

• Why did these crevasses form?

Crevasses on an Antarctic Outlet Glacier

R.P. Sharp. 1988.Living Ice

Ice accelerated into a valley through the Transantarctic Mountains, then slowed down and spread sideways.

• When did each set of crevasses form?

Flow direction

The Curious ScientistQuestions on flow, deformation, and

crevasses…

Five-minute questions for your group …• Recorders please turn in reports at end of class.

1. Where are those Rocks Now?You put a straight line of 5 stones across a

glacier in its accumulation area. They got buried, and they will be carried along by the ice. Eventually the ice encasing them will melt in the ablation area.

• One year after you laid them out, which of the stones was closest to the terminus?

• Which stone will probably reappear first at the surface in the ablation area?

• Which stone will go the deepest into the glacier before it eventually starts to re-emerge?

• Which stone will reappear closest to the terminus?• What will happen to the stones after they reappear at the

surface?

2. Crevasses on a Cascades GlacierCrevasses tend to open up at right angles to the direction where ice is stretched the most, i.e. like a rope of silly putty, the ice tends to break clean across the direction in which you are stretching it the most.

Suppose that you are climbing in the Cascades, and you have been told to watch out for crevasses on Glacier X near the equilibrium line.

• Using the figure showing how a line of stones across a glacier is deformed by flow, suggest which way the crevasses might run near the glacier edge, and why.

0

31

2

3. Alaskan Glaciers

http://www.antarcticglaciers.org/modern-glaciers/structural-glaciology/splaying-crevasse/

• Locate examples of all 3 types of crevasses (transverse, marginal, and splay) and explain why they formed.

4. Crevasses on Saskatchewan Glacier

Google Earth

• Locate examples of all 3 types of crevasses and explain why they formed.

Direction of flow

Direction of flow

4. Crevasses on Saskatchewan Glacier

Google Earth

• Locate examples of all 3 types of crevasses (transverse, marginal, and splay) and explain why they formed.

Direction of flow

Direction of flow

Ice-Age World

• What was it like … ?• How did it end … ?

At 20 ka BP, Earth was in the grip of an Ice AgeOr, as Macdougall would remind us, taking the longer

view, Earth was in the grip of the most recent cold period of the current Ice Age.

• Thick ice sheets covered large areas.

• The ice sheets needed a combination of moisture and cold temperatures to form and survive.

Where was the Ice?• Laurentide Ice Sheet (Eastern/central North America)• Cordilleran Ice Sheet (Western North America)• British Ice Sheet• Iceland• Greenland• Fennoscandian Ice

Sheet (Scandinavia)• Siberian Ice Sheet

(limited by low accumulation?)

• Barents Sea Ice Sheet (marine ice sheet - wet feet)

Where was the Ice at 20 ka?

We know a lot about ice-sheet retreat during the past 20 ka, but not so much about earlier history.

• Why not?

Green colors indicate areas that were dry land.Sea level was much lowerthen (by ~120 meters).• Why?

Ice Map - A Norwegian perspective

https://icemap.rhewlif.xyz/

https://icemap.rhewlif.xyz/

Anderson and Borns, 1994. The Ice Age World

Fennoscandian Ice Sheet - 20kaIce sheet

Ice Shelf

Icebergs+Sea IceGlacier

Ice-dammed lakeOpen ocean

Sparse vegetationGlacial sedimentsGrass or brush

Grass or brush

Polar desert or tundra

Tundra or steppe

Partly forestedSteppe or parkland

Grass or brushGrass/brush+loessPartly forested


Fennoscandian Ice Sheet - 20ka

• Sea-ice cover to Spain (in winter).

• Fennoscandian and British ice sheets may have been joined.

• Europe covered by tundra and steppe, like northern Canada or Siberia today.

• Low sea level, English Channel dry.Why?

• Black and Caspian Seas are lakes. Why?



• Fennoscandian and British ice sheets have separated.

• Barents Ice Sheet is disintegrating.

• Sea level is still low.

• Black Sea is still a lake.

• Still few trees north of Pyrenees, Alps, or Caucasus.


Fennoscandian Ice Sheet – 12-11ka

Tundra/park tundra

Tundra/steppe park

Alpine vegetation

Steppe/parklandParkland+forestBirch forest

Birch/pine/spruce

Boreal:pine/spruceMixed boreal/broadleaf

Broadleaf /hazel

Allerod limit - birch


Fennoscandian Ice Sheet – 12-11ka• North Atlantic open in

summer ~12.5 ka.• Sea ice re-advanced in

Younger Dryas cold period 12-11 ka.

• British Ice Sheet is largely gone.

• Sea level is rising.• Barents Ice Sheet

disintegrating.• Baltic Sea is a lake.• Caspian Sea is now a

closed basin.• Black Sea still a lake.• Forests re-occupy

Europe.

Andersen and Borns, 1994. The Ice Age World

Fennoscandian Ice Sheet – 9.5ka

• Yoldia Sea in Baltic area

• UK still connected to Europe

• Sea ice rare around Europe

• Less ice on Iceland

• Forests moving north



• Only a small ice cap left on Norwegian mountain spine.

• Only a few small ice caps in Iceland.

• Sea ice rare around Europe.

• Baltic Lake• Sea level still lower

than today • parts of North Sea

and English Channel are dry


North America 20-18ka

GlacierIce sheet

Ice shelfIce-dammed

Open ocean

Pluvial lake

Sea ice

Park tundraDesert/tundra

ConifersBroadleaf

• Cordilleran ice sheet (C) operated independently from Laurentide (L) and Keewatin (K) domes.

• Connection to Greenland Ice Sheet(?)

• Ice-free areas in Alaska (why?)

• Bering Strait is dry.


North America 15ka

GlacierIce sheet

Ice shelfIce-dammed

Open ocean

Pluvial lake

Sea ice

Park tundraDesert/tundra

ConifersBroadleaf

• Southern margin retreating.

• Surge lobes advance on soft wet bed

• Cordilleran and Keewatin Ice Sheets starting to separate (Why?)


North America 11ka

• Forests advancing northward

• Baffin Bay free of glacier ice

• Ice-marginal lakes (Why?)

• Cordilleran and Keewatin/Laurentide ice sheets separated

• Importance for humans?

Dyke and Prest, 1989.

Laurentide Ice Sheet – 8.4ka

• Why are there big lakes along southern margin?

• Cochrane Lobe surge into Lake Ojibway.

• Hudson Bay Dome collapses.

• Drainage of marginal lakes Agassiz and Ojibway.

Dyke and Prest, 1989.

Laurentide Ice Sheet – 7.9ka

• Sea level was still lower than today.

• Sea enters Hudson Bay -extensive flooding• How could there be

flooding?

• Remnants of ice sheet remain in Ungava (northern Quebec) and on Baffin Island/Foxe Basin.

Laurentide Ice Sheet and Climate

A huge lump of ice several km high can affect persistent low-pressure systems, wind patterns, and jet stream.

• Jet stream diverted south, takes Seattle weather to California.

• Jet diverted north, then sweepssouth from Arctic down over Atlantic, cooling Europe even more.

Great Ocean Conveyor

(From the IPCC Report 2001)

Ocean “conveyor” driven by formation of sea ice in North Atlantic and around Antarctica

Conveyor may have been off frequently during the Ice Age, contributing to very cold European climate.

• Salt excluded from freezing sea ice makes the water dense.

• It sinks, and new warm water is drawn in to replace it.

Western Lakes

• Large pluvial lakes(formed by rainfall) in USA where there are only deserts today.

• Lahontan, Bonneville (Salt Lake) drained to Columbia River.

• Their shorelines are still visible.

• Why was that area so different from today? (the continental ice sheet was hundreds of miles away, and did not drain into these lakes.) Andersen and Borns, 1994. The Ice Age World

Lake Bonneville and Lake Provo shorelines


330 m above Great Salt Lake

Provo Valley, Utah

Mendelova, M. et al. (2017) Geographical Res. Letters 43(2), 719-0750

High precipitation from strong Westerlies

Ice-age Patagonia

Ice Age ice sheet

Modern ice caps

Mendelova, M. et al. (2017) Geographical Res. Letters 43(2), 719-0750

Big glaciers excavated the

modern Argentine

lakes

Antarctica leaves the Ice Age• Larger West Antarctic Ice Sheet (WAIS) at 20ka BP. • Embayments with floating ice shelves today may have had

thick, grounded ice.

• East Antarctica probably saw minor change, • It could not expand very far, because of narrow continental shelf.

• West Antarctic grounding-line retreat may have been near-continuous ever since ~8 ka BP, and it is likely to continue to shrink.

Documents

ESS 203 -Glaciers and Global Change · On a rocky bed: •Higher water pressure "floats" ice. •Higher pressure reduces friction with the bedrock. •If bed is "rough", high pressure