Why do Glaciers Move?
One of the simplest explanations for why glaciers move is this: Glaciers are made of ice (that’s frozen water). In a way, glaciers are alive and subject to the effects of temperature, sunlight and wind, among other things. Think of a glacier as a huge frozen river. We can see the end of this river of ice where it stops.
That bit of information would explain part of the reason that glaciers have been receding all over the planet. For example, one huge glacier in New Zealand has almost disappeared in comparison to its status just 15 years ago. The river of ice is melting and becoming much smaller. And it’s doing it very quickly.
Atmospheric conditions such as sunlight and elevated temperatures aren’t the only reason glaciers are receding at alarming rates. Some of the chemical content of the air also causes ice to melt. This contributes to the loss of mass in glaciers.
But what about the movement of a glacier down the valley? Pressure and gravity have something to do with this. The huge mass of ice at the mouth of the glacier (the end we can see) is subject to a lot of pressure. Heat associated with this pressure and with warm air temperatures causing ice at the mouth of the glacier to melt. Ice from above then has room to move downward to replace the melting ice.
Glaciers move very slowly because of this process, sometimes only an inch a day or less. If there is insufficient moisture and ice at higher elevations the melting ice at the mouth of the glacier won’t be replaced. There isn’t enough ice/weight to push down and constantly renew the glacier.
Within the glacier there are ice crystals that can move rather easily due to less pressure. Internal movement of the ice mass also helps move the glacier forward. A huge glacier may move several feet on rare occasions. In fact, one glacier in the Himalayan Mountains moved a few miles in a matter of months. This is extremely rare, of course. A combination of factors caused the mass to move so far and so fast.
As mentioned earlier, if there is not enough snow at higher elevations to create new flows of moisture the glacier may be seen to retreat. Just as it is rare to see a glacier move several miles, it is rare to see glaciers recede long distances. But this has become a bit more common in recent years. Perhaps because of warmer air temperatures and other factors, some glaciers have receded consistently over the past few years.
Other glaciers have moved forward several feet in a period of days. One Alaska glacier moved several meters each day in the mid-1980s. In fact, the effect of this rapid advance was the closing off of an area that ultimately filled with water, creating a new lake. Glaciers are massive objects when viewed as a whole. Glacier movement can affect much of the surrounding area.