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A. Introduction

Learning outcomes - You should be able to:

• describe the components of glacial mass balance;

• explain the processes affecting glacial mass balance and equilibrium line elevation;
• discuss the impact of mass balance gradient on glacier flow rates; and
• classify glaciers based on their mass balance

Glaciers classified based on:

• morphology

• temperature

• mass balance

B. Mass Balance Classification

Classes:

• advancing, stationary, retreating

• 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

C. Calculating Mass Balance

Components accumulation ablation climatic influence precipitation mean summer temperature albedo: % reflected solar radiation 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)

equilibrium line (snow line) 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. ELA increases with: decreasing snowfall increasing temperature negative net mass balance distance from moisture source Measurements balance year; winter balance, summer balance bn = bw + bs direct measurements: stakes, snow pits remote sensing measurements

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.

D. Relationship to Glacier Flow

Flow:

provides dynamic link between accumulation and ablation subsystems

ice discharge: ice volume 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

E. Summary

Mass Balance

• accumulation, flow, ablation

• summer, winter, net

• advancing, retreating, stationary

Current Global Picture

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