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Geology 370: Glacial Geology

GLACIAL MASS BALANCE

A. Introduction

• survival of glaciers (first outline)

• current conditions

Image credit: graph and map from R.A. Rohde (2006) Global Warming Art http://www.globalwarmingart.com/wiki/Image:Glacier_Mass_Balance_png

Image credit: 2004 Bruce F. Molnia, USGS; 1941 W.O. Field, National Snow and Ice Data Center. Image composed by R.A. Rohde (2006) Global Warming Art http://www.globalwarmingart.com/wiki/Image:Muir_Glacier_jpg

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B. Components

1. Accumulation 2. Ablation processes climatic influence precipitation exposure to solar radiation mean summer temperature albedo: percent of solar radiation reflecte fresh dry snow 80-97% firn 43-69% clean ice 34-51% dirty ice 15-25% debris covered ice 10-15% (source: Benn & Evans, 1998, p. 70)

3. Equilibrium Line (snow line)

• ELA: equilibrium line altitude

Image credit: Austin S. Post (1961) Tenas Tikke Glacier. From the Online Glacier Photograph Database. Boulder, Colorado USA: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media.

Image credit: Austin S. Post (1960) Honeycomb Glacier. From the Online Glacier Photograph Database. Boulder, Colorado USA: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media.

• ELA rises with:

  • decreasing snowfall

  • increasing temperature

  • negative net mass balance

  • distance from moisture sources

4. Glacier Flow

• Provides dynamic link between accumulation and ablation subsystems

• Ice discharge: volume of ice passing through the equilibrium line during the balance year (m³/year)

• Flow rate dependent on:

  magnitude of input and output

 

net balance gradient: increase in net balance with altitude 

• the higher the gradient, the faster the flow

• gradients steeper in maritime climates than continental climates

• gradients steeper in temperate latitudes than in polar latitudes

 

 

 

 

 

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C. Net Mass Balance

1. Balance year

2. Stationary, advancing & retreating glaciers

3. Measurements

• direct measurements: stakes & snow pits

• remote sensing methods

• hydrological method

B_n = P - R - E

B_n = net mass balance
P = precipitation
R = runoff
E = evaporation

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D. Summary

Greenland thinning due to ice melting and faster ice flow to the sea.

Image credit: NASA Visible Earth; NASA GSFC Scientific Visualization Studio. http://visibleearth.nasa.gov/view_rec.php?id=655

Image credit: 2004 Bruce F. Molnia, USGS; 1909 Ulysses Sherman Grant, USGS. Image composed by R.A. Rohde (2006) Global Warming Art http://www.globalwarmingart.com/wiki/Image:McCarty_Glacier_jpg