Geo563_2 Ice and Thermal Prop!1!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!2!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!3!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!4!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!Geo563_2 Ice and Thermal Prop!5!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.!Geo563_2 Ice and Thermal Prop!6!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!Geo563_2 Ice and Thermal Prop!7!Geo 563_3. icepropthermal regime!WARM BASED GLACIERS!GLACIER BAY