Glaciers grow through a process called accumulation and waste away through a process called wastage, or ablation. Learn about these processes and how they are used to determine the health, or mass balance, of a glacier.
Did you ever wonder what life would be like without glaciers? Well, for starters, if all of the world’s glaciers melted at once, sea level would rise about 215 feet. That means if you currently live on the beach, you would have to move to the 22nd floor of the nearest hotel just to stay afloat.Glaciers are masses of ice that form in areas of the world where snow falls more often than it melts.
This builds layers of snow that compress due to the increasing weight, eventually turning the mass into glacier ice. Glaciers are impressive to see, but they’re not just stagnant blocks of ice; they are actually dynamic structures that move, grow and recede under different conditions
When a glacier is growing, we use the term ‘accumulation,’ which means ‘the addition of snow and ice to a glacier.’ There are different processes that factor into accumulation, with a common factor being snowfall directly onto the glacier. But we also see that accumulation occurs when other forms of precipitation hit the ice mass, such as freezing rain. Snow does not have to fall directly onto the glacier. In fact, significant accumulation can be attributed to wind-blown snow that settles onto the glacier or snow that flows onto the glacier via an avalanche.
The opposite of accumulation is ablation, or wastage, which means ‘the removal of snow or ice from a glacier.’ Most ablation occurs due to melting during the warmer months of the year, but it can also be the result of wind erosion that blows snow from the glacier or sublimation, which is the direct change from a solid to a gas. In other words, with sublimation, ice can directly change into vapor, bypassing the liquid water phase.Calving is another form of ablation in which large chunks of ice break off the glacier and fall into the water. This can be a dramatic sight and can be accompanied by a loud crack. Calving gives birth to floating masses of ice called icebergs.
You can recall this term by remembering that cows give birth to calves and glaciers ‘calve’ icebergs.
Glacier Mass Balance
As we mentioned, glaciers are dynamic structures, and they change throughout their lifetime. They are said to be retreating if the leading edge of the glacier does not travel as far as it previously did because ablation exceeded accumulation. On the other hand, a glacier is said to be advancing if the leading edge of the glacier moves forward faster than the rate of ablation. Scientists determine if a glacier is retreating or advancing by measuring where the terminus, or leading edge of the glacier, is located.
The terminus is sometimes called the snout of the glacier, as if the glacier is being led by its nose.Knowing the location of the terminus helps scientists determine the glacier mass balance, which is simply the balance between accumulation and ablation. If there is equal balance between these two factors, then a glacier is said to be in equilibrium and it does not change in size.
It might help you to think of the mass balance as the health of the glacier.For example, if there is more growth than melting, then the glacier is gaining mass and looking healthy. These growing glaciers are said to have a positive mass balance, and they will advance. Consequently, if there is a loss of mass due to faster wasting than growth, the glacier will be sick; there is a negative mass balance and the glacier will retreat.
Let’s review. When a glacier is growing, we use the term ‘accumulation,’ which means ‘the addition of snow and ice to a glacier.
‘ This happens due to different processes, including snowfall or freezing rain directly hitting the glacier. Accumulation can also be attributed to wind-blown snow or avalanche snow that settles onto the glacier.The opposite of accumulation is ablation, or wastage, which means ‘the removal of snow or ice from a glacier.’ Ablation occurs due to melting, wind erosion and calving, which is when large chunks of ice break off the glacier and fall into the water. The floating masses of ice are called icebergs. Sublimation is the direct change from a solid to a gas.
The glacier’s terminus, or snout, is defined as the leading edge of the glacier. By knowing the location of the terminus, scientists can determine if a glacier is retreating or advancing. ‘Retreating’ means the leading edge of the glacier does not travel as far as it previously did because ablation exceeded accumulation. ‘Advancing’ means the leading edge of the glacier moves forward faster than the rate of ablation.The glacier mass balance is the balance between accumulation and ablation. If there is equal balance, then a glacier is said to be in equilibrium and it does not change in size. If there is more growth than melting, then there is a positive mass balance and the glacier will advance.
If there is a loss of mass due to faster wasting than growth, then there is a negative mass balance and the glacier will retreat.
After this lesson, you should be able to:
- Differentiate between accumulation and ablation and explain how each occurs
- Define calving and sublimation
- Recall what knowing the location of a glacier’s terminus can tell scientists
- Explain what glacier mass balance is