Asked by Murtaza
Hi Murtaza,
The easiest way to think about mass balance is to liken it to a bank account. If you consistently have more going out than coming in, over time your bank account will decrease in size. If you consistently pay in more than you spend, your bank account will grow.
It is the same with glaciers. If the mass balance is negative, the glacier will shrink; if it is positive it will grow; if it is in equilibrium (melt = accumulation), the glacier will be stable. If the size of the surfeit decreases, but accumulation is still greater than ablation, the glacier will continue to grow (although the rate of advance might slow).
The other thing to think about is that glaciers are great smoothers of climate. They respond to long-term trends rather than annual or shorter timescales. One big dump of snow will not make the glacier advance noticeably. The timescale it takes for a glacier to respond is the response time.
Finally, mass balance isn’t always the only control on glacier size. Iceberg calving in marine-terminating glaciers may strongly control glacier ablation. In addition, although glaciers might sometimes advance, this isn’t always as a result of a positive mass balance – they may be thinning or stretching (perhaps in response to calving dynamics), but still have a smaller volume of ice.
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