Geo563_2 Ice and Thermal Prop

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Geo 563_3. icepropthermal regime

Ice and Snow Facies, �Thermal Regime of glaciers

Background glaciology Geo 563_3. icepropthermal regime

What is a Glacier? :� large mass of perennial ice that originates on land by densification of snow AND it shows evidence of past or present movement.

•  Wide distribution of where glaciers occur – E.g. Antarctica -- -88oC at 3500 m elev.with

annual precip of ,10 cm/yr., low S/W temps – New Zealand Alps, low W temps but warm

humid, lots precipt of snow, get 100’s cm/yr – Other examples. …

•  Defines differences in activity -- so….

USGS Atlas Series of World’s Glaciers •  All glaciers combined = about 80 of global

sea level •  http://pubs.usgs.gov/pp/p1386 ,and then add

letter for each chapter A through K •  B Antarctica •  K Alaska •  C Greenland etc.

Geo 563_3. icepropthermal regime

Bering Glacier -- NASA Geo 563_3. icepropthermal regime

ASTER image of Glacier San Quintin, an outlet glacier on the west side of the North Patagonian Icefield. .. Univ Aberystwyth web site

Kaskawulsh Glacier, Yukon, Univ UBC

Geo563_2 Ice and Thermal Prop

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Geo 563_3. icepropthermal regime

Snow and Ice = expressed in meters (or mm) of water equivalent

•  E.g., 5 m of snow @ density of 0.4 gm/cm3

•  = to 2 m3 H20 equiv.

1m3

Geo 563_3. icepropthermal regime

Different shapes at different temperatures and humidity; higher humidity means more delicate structures.

Snowcrystals.com

Geo 563_3. icepropthermal regime

Geo 563_3. icepropthermal regime

The water molecules in ice form a hexagonal lattice as shown at right (two views of the same thing). Each red ball represents an oxygen atom, and the grey sticks represent hydrogen atoms. There are two hydrogens for each oxygen, making the usual H2O.

Geo563_2 Ice and Thermal Prop

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Geo 563_3. icepropthermal regime

Glaciers maintained by Snowfall

•  Snow -- density (ρ) 0.05g/cm3

–  Add wind -- varies 0.1 to 0.4 g/cm3

•  Firn -- transitional 0.4 - 0.83 g/cm3

–  @0.83 g/cm3 -- all air passages sealed off

–  Increase in density to 0.914 due to compression of ice bubbles

•  Glacial ice -- ρ = 0.914 g/cm3

Geo 563_3. icepropthermal regime

Processes of Metamorphism •  Equilibrium Temperature - rounding of grains;

sintering - via sublimation –  transfer of vapor to points of contact; rounds the

grains and strengthens “necks” between grains. Due to differences in saturation vapor pressure

•  Temp. gradient -- depth hoar with increase in grain size and decrease in strength – See overhead and handouts….

•  Melt-Freezing •  Compaction and settling-reduces surface area

Geo 563_3. icepropthermal regime

Raynaud, 1992 Gases within bubbles = palaeo atmospheric air Geo 563_3.

icepropthermal regime

Firn-ice transition • Depth of transition depends on surface temperature and accumulation rate • Camp Century, Greenland: ~68 m below ice sheet surface • Vostok, Antarctica: ~100 m below ice sheet surface

Low precipt and cold = long time to make ice

High precipt and warm =short time to make ice

Geo563_2 Ice and Thermal Prop

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Geo 563_3. icepropthermal regime

Gas age v ice age: Vostok, Antarctica Differences in ∆t through time are a function of changes in accumulation rate (from Barnola et al., 1991)

Geo 563_3. icepropthermal regime

Geo 563_3. icepropthermal regime

Thermal Regime of Glaciers - important! -- basal temperature & vertical gradients in ice

•  Ice velocity •  Erosion rates (landforms) •  Deposition rates (landforms) •  Hydrology and plumbing system (landforms) •  Mass balance (see page 74) •  Response time

Geo 563_3. icepropthermal regime

Geophysical Classification �(Ahlmann, 1935)�

-based on ice surface temperature and surface melting

•  1. High polar or cold based glaciers –  No surface melt, no

outwash, •  2. Subpolar Glaciers

–  Surface melt in summer •  3. Temperate or warm-

based glaciers –  Ice at the pressure melting

point thru’ the most of the year From Bill Locke

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Geo 563_3. icepropthermal regime

Pressure melting point

•  Increasing pressure with depth forces ice towards its more dense, liquid phase.  Thus, the melting point of ice decreases at about 0.7oC per vertical kilometer of ice.  If basal ice is at the PMP ("warm-based"), heat cannot escape, thus the presence of meltwater is assured.   Also, ice may locally melt in high pressure regions and freeze in low-pressure regions, leading to regelation.

Freezing temp goes down as pressure goes up at -1oC/140 bars where

~1 bar = 100 kPa = 14 lb/in2 Geo 563_3. icepropthermal regime

Basal Temperature Classification �(-based on bed temperatures

•  cold based glaciers –  Below PMP, frozen to the

bed, all movement is from internal deformation of the ice, less erosion

•  wet-based glaciers –  At or near the PMP at the

bed, water at the bed, more slip and erosion; due to geothermal heat and friction

From Bill Locke

Geo 563_3. icepropthermal regime

Truth! Many glaciers are �

polythermal •  cold based sections and

warm-based sections of same glacier

•  Transitions from one regime to another in space and over time.

From Bill Locke Geo 563_3. icepropthermal regime

Rippin, D.M., Willis, I.C. and Kohler, J. Submitted. Rapid changes in the thermal regime of the polythermal glacier Midre Lovénbreen, Svalbard in response to a changing climate. Journal of Geophysical Research.

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Geo 563_3. icepropthermal regime

Shaded surface digital elevation model (DEM; elevations in metres) of Midre Lovénbreen derived from 2005 LiDAR data. DEM resolution is 20 × 20 m. Red tracks mark the GPR survey lines collected in 2006 over the trunk of the glacier (Willis etal, 2003)

Geo 563_3. icepropthermal regime

http://www.spri.cam.ac.uk/research/projects/polythermalglaciers/

Geo 563_3. icepropthermal regime

May 1990

GPR tracks on Midre Lovenbreen Blue = cold based ; red is warm basal ice

May 1998 May 2006

http://www.spri.cam.ac.uk/research/projects/polythermalglaciers/

Geo 563_3. icepropthermal regime

Taylor Glacier and Lake Bonney - Michael Hambrey

Rhone Glacier on the flank of Taylor Valley, in the Dry Valleys of Victoria Land, Antarctica. Photo M. J. Hambrey, 2001. (WWW.SWISSEDUC.CH)

COLD BASED ICE

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Geo 563_3. icepropthermal regime

WARM BASED GLACIERS GLACIER BAY ALASKA Photo from USGS

Geo 563_3. icepropthermal regime

Equilibrium Line Altitude (ELA): The long-term average position of the highest (late summer) firn line. The ELA is where the amount of accumulated snow and ablated water are equal. • The ELA is climate and location dependent.

The ELA can be a significant indicator of glacier health. Warming will raise the elevation of the ELA. Because there is a greater area of the glacier below the ELA, a mountain glacier will retreat uphill.

• Accumulation Zone - area where snow can accumulate and is not melted in the summer• Firn Line - seasonal boundary between old ice (below) and recrystallized new snow (above)• Ablation Zone - area where snow is melted during the summer.

Glacier Facies

Geo 563_3. icepropthermal regime

Carl Benson’s zones……pg 67 in Benn and Evans fig2.2

Geo 563_3. icepropthermal regime

Brigham Young University

Carl Benson

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Geo 563_3. icepropthermal regime

Marco Tedesco Professor City College of New York, City University of New York. He is also affiliated with the NASA Goddard Space Flight Center, US, and fellow of the University of Maryland, Baltimore County

100 to 175km east from the coast of western Greenland and depicts the surface of the ice sheet as observed by synthetic-aperture radar. The left image was acquired by Japanese Earth Resources Satellite-1 "Fuyo-1" in October 1992, and the right one, by the Advanced Land Observing Satellite "Daichi" in August and in October of last year (2008). http://www.eorc.jaxa.jp/en/imgdata/topics/2009/tp090128.html Geo 563_3.

icepropthermal regime

http://nsidc.org/arcticseaicenews/ Sept 17, 2009