THE MASS BALANCE CONCEPT

A reminder of the Glacial Budget System:

The balance betweeen accumulation and ablation over time is what controls the development of a glacier system over time. This relationship is known as the glacial budget (or mass balance).

Positive Mass Balance - this occurs where accumulation is greater than ablation - resulting in an increase in the ice mass and the ice front advances (usually the case in winter.

Negative Mass Balance - this occurs where ablation is greater than accumulation - this results in a decrease in the mass of ice and the ice front retreats (usually the case in summer)

Equilibrium - occurs where accumulation is equal to ablation

Over the course of a year, glaciers expand and contract due to seasonal changes in the mass balance. The net mass balance - which is calculated from the time of minimum mass in one year to the time of minimum mass in the next year (usually autumn - end of summer melting) will determine whether a glacier has advanced ('grown') or retreated ('shrunk').

Click here for an animation of an advancing glacier.

Lesson Resources (Handouts and Extra Links)

Handouts / Lesson Resources:

Read: Yates and Palmer (2005) "Advanced Geography" p.324-325 and Waugh (2000) "An Integrated Approach (3rd ed)" p.106

Suggested Background Reading:

An animation: A positive mass balance and advancing glaciers (external link)

An animation: Demonstrating the annual glacial budget (external link)

Glacial Budget (external link)

The Glacial Budget (A summary) (external link)

Alaskan Glaciers Melting Faster (BBC News Article - July 2002)

An Introduction to Glacial Systems – including overview of Mass Balance (and reference to glacier movement) (external link)

Mountain Glacier Fluctuations – changes in mass balance (external link)

Advance and Retreat of Glaciers (Animation - External Link)