• Glaciers cover 10% of all land area
• 84%-Antarctic
  • Introduction to Antarctica <http://www.glacier.rice.edu/invitation/1_introduction.html>
  • Virtual Antarctic <http://www.doc.ic.ac.uk/~kpt/terraquest/va/>
    • Snow and Ice <http://www.doc.ic.ac.uk/~kpt/terraquest/va/science/snow/snow.html#A>
    • Climate <http://www.doc.ic.ac.uk/~kpt/terraquest/va/science/climate/climate.html>
• 11%-Greenland
• 4%-other areas

  USGS Factsheets on the worldwide distribution of glaciers

  • Areal Extent of Present-Day Glaciers World Glaciers (USGS) Map
  • Estimated Present-Day Area and Volume of Glaciers and Maximum Sea level Rise Potential

 Independent variables

• Altitude: influences local temperature (Lapse rate = ±9.8-4°C/km--air cooling with decreasing pressure) and precipitation patterns
•  Latitude: Controls total annual solar radiation. The higher the latitude the lower the regional snowline
•  Relief: Glaciers need a relatively flat surface on which to develop.
  • Regions of steep variable relief generally have variable snowlines owing to steep slopes that inhibit ice formation, and snow avalanching that nourishes adjacent valley floors
•  Orientation (Aspect): Influences the amount of solar radiation and wind blown snow recieved
  • Exercise: Go to World Glacier inventory, (1) select extract selected regions and (2) choose North America Puget Sound and the Cascades (3) Choose glacial number and orientation of accumulation zone. n (4) Analyse th date. Is there a pattern? If so then explain it.
• Distance from the ocean and dominant wind pattern: Affects amount and distribution of precipitation. Coastal mountains typically have healthier glaciers.
• Dependent variables
• Temperature: The snowline lies around the 0° isotherm for most glaciers, and around -4° for ice shelves.
•  Precipitation: Glaciers cannot exist without precipitation.
  • important variables: Volume, type, timing, net annual precipitation (P-E)
  • Nivometric coefficient (snowfall effectiveness) = Annual snowfall/total annual precipitation
    • If both are high, glacial growth will occur
    • If NC is high (1) and P is low, the glacier will be stable but not very dynamic (eg. Antarctic Ice Sheet)
    • If NC is moderate and P is high, the glacier will be less stable but may be very dynamic

• *** The spacial distribution of Alpine Glaciers and snowlines Rachel Waldinger GRG 394K, University of Texas
• An Introduction to Glaciers across Space Megan O'Conner and Sara Lyle, University of Montana

The snowline marks the elevation above which snow remains all year around. The equilibrium line elevation (ELA) is the region of the glacier where the amount of input is equal to the amount of output. Typically the snowline, as observed at the end of the melting season, approximates the location of the equilibrium line. However, the zone of accumulation may contain superimposed ice, formed by the direct freezing of melt water to the glacier's surface. Where superimposed ice is present the ELA is displaced down glacier from the snowline.

Transient Snowline:

-Changes seasonally. During the winter it may extend to the snout of the glacier.

Annual snowline:

The line above which snow remains during a given year.

• Can you identify the snowline on the Trapridge Glacier? An alpine surge-type glacier in the St. Elias Mountains, Yukon Territory. Image from Dr. Barry Narod's Glaciology at UBC, University of British Colombia.

Orographic snowline:

A variable snowline caused by variations in insolation resulting from orientation and local topography (i.e. Steep, well exposed mts. vs. shaded slopes with room for accumulation) 

Regional snowline:

The change in snowline with latitude as viewed through a region.

 

Approximating the regional snowline

• Approximation of current snowline from maps using slopes having the same orientation (Flint, 1971)
  • Plot the summit elevations of lowest peaks containing glaciers
  • Plot the summit elevations of highest peaks lacking glaciers but having slopes gentle enough to support them
  • The snowline/ELA would lie somewhere in between
• Approximation of current snowline snowline/ELA e based on glacial contours
• All else being equal (e.g. slope) glacial contours tend to be concave in the down-ice direction in the zone of accumulation and concave in the up-ice direction in the zone of ablation. The snowline should be located in that region where contours are parallel.
• Approximating a past regional snowline using the elevation of cirque floors
  • Assumption:
    • The floor of a young cirque glacier approximates the 0° isotherm and local snowline
    • Once the cirque glacier develops into a valley glacier the floor is lowered below the snowline
    •  The snowline can therefore be approximated by plotting the elevation of small cirque basins 
• Approximating a past regional snowline using in the field
  • Past snowlines/ELAs can be determined my the detailed mapping of glacial features, trimlines, soils and weathered surfaces

•  Calculating equilibrium-line altitudes of former glaciers by the balance ratio method: a new computer spreadsheet, Glacial Geology and Geomorphology, 1997, Benn and Gemmell. Yet another method of estimating ELA. This method is also discussed in your text.
• The spacial distribution of alpine glaciers and snowlines: influencing factors and controls, 1999, Rachel Waldinger (student), University of Texas
• NPS introduction to glaciers
• USGS Aster Glacier Footprint Viewer
• **** USGS: Completed portions of the Satellite Image Atlas of Glaciers of the World
  • Trevor J.H. Chinn 1, 2000, Satellite image atlas of glaciers of the world, Glaciers of Irian Jaya, Indonesia, and New Zealand <http://pubs.usgs.gov/prof/p1386h/nzealand/nzealand.html >
  • Satellite image atlas of glaciers of the world, South America, http://pubs.usgs.gov/prof/p1386i/title.html
    • Lliboutry, Glaciers of Chile and Argentina
• U.S. Geological Survey Professional Paper 1386-J, Satellite Image Atlas of Glaciers of the World, North America,, Edited by Richard S. Williams, Jr., and Jane G. Ferrigno http://http://pubs.usgs.gov/prof/p1386j/