Do Glaciers Actually Move?

Guest

I like what you are teaching / researching. Please help me better understand this idea.

What is happening to the glacier you are researching? Is it moving? If so, at what rate and in which direction?

Joined: 23 Mar 2004 Posts: 64

Great question Candy!

The movement of glaciers has been studied for many years and it is an exciting phenomena. The Linne Glacier near Isfjord Radio at Kapp Linne in Svalbard Norway is a focus of research for some of the student researchers in this project. Here are some terms that might be useful. Ablation refers to a reduction in the total mass of a glacier. Accumulation refers to an increase in a glacier's mass. The Linne Glacier is currently receding, meaning its rate of ablation is currently greater than the rate of accumulation.

So, how does a glacier move? Glaciers move by processes referred to as basal sliding and/or internal deformation (plastic flow). Glacier movement is a dynamic process. Perhaps a collection of processes might be a better way of describing it! The movement of glaciers is a powerful force that carves out landforms by eroding rock materials and depositing these, essentially altering the landscape in dramatic ways.

Glaciers move from high elevations to lower elevations with the help of gravity. The movement of the glacier depends on several factors. These include such factors as day-to-day weather conditions including temperature, wind conditions, precipitation, and solar radiation, the seasonal climate changes, the mass and density of the glacier, the degree of slope (steepness) of the area on which the glacier resides, the slope of the upper surface of the ice, and the amount of debris the glacier is carrying . Glaciers are fed by snowfall. The thickness, temperature, and pressure of the ice are all characteristics that affect the rate the glacier will flow. In general, the thicker the ice is, the faster the flow, due to internal deformation. The higher the temperature of the ice is, the faster the movement. The greater the pressure is, the faster the movement.

There are certain basic processes that contribute to the movement of glaciers. One process is internal deformation, also known as plastic flow. It occurs when the ice particles continuously deform and reform, changing shape due to the pressure of the overlying snow and ice and the force of gravity. As a result of this continual change, the particles of ice slip past each other to create a forward movement. This type of movement characterizes the glaciers seen in the Svalbard area where we are researching. The glacier freezes and adheres to the land beneath it. Movement due to internal deformation is a slower process than movement due to basil sliding as described below.

When the movement of a glacier is due to basil sliding (sometimes called basil slip), the movement occurs at its base. The ice does not adhere to the land below it. The weight of the glacier sliding over the surface results in some of the ice partially melting at the base of the glacier. The high pressure reduces the temperature at which ice will melt. If you think about what you know about water freezing, you might think that ice will only melt if the temperature is above °C. Actually, the thicker the ice, the lower the temperature at which it will melt resulting in more water that is available at the base of the glacier to make movement easier. This meltwater mixes with sand and gravel and creates a slush that reduces friction and surface tension and allows the glacier to easily slide over the watery layer. This thin layer of water beneath the glacier may be due to the pressure referred to above, or it may be due to rain or surface meltwater that has worked its way through the cracks in the ice, or even from melting that is occurring at higher elevations of the glacier that is flowing towards the terminus or end of the glacier. Glaciers that move by basil sliding are much faster than those moving by internal deformation.

Deforming substrate sometimes contributes to the flow or movement of a glacier due to the nature of the sediments or rock debris under the ice sheet. If the glacier is on a bed consisting of soft sediments with some water available, the sediments can move and carry the ice along with them.

A glacier begins moving once it accumulates enough mass to start the process. Basically, a glacier is always moving forward, due to the force of gravity. This is true whether it is advancing, retreating, or relatively stationary. However, if the rate at which the glacier is melting is equal to the rate of movement, it is considered to be stationary. If the rate of melting is greater than the rate of movement, the glacier is receding. If the rate of movement exceeds the rate of melting, it is considered to be advancing.

Quite common in Svalbard is the situation where the snowline of the glacier is close to sea level. Great blocks of ice break off, becoming icebergs. When a block of ice breaks off to form an iceberg, the process is called calving.

Glaciers in Svalbard are mostly moving by internal deformation. Even while we are here during the late summer, ice dominates Svalbard, covering 60% of the landscape. If you look at the photographs I have posted in the album, you may see large areas of land not covered by ice, but remember, this area is closer to sea level in elevation and quite near the shoreline. In north eastern Svalbard, there are huge ice caps that totally cover the underlying bedrock, often reaching all the way to the sea and forming a high ice wall. The glaciers most prevalent in the area where we are researching are large, but not quite so large as in the north east! They cover large areas with the mountain peaks projecting above them. The glaciers in Svalbard have mostly been considered to be retreating glaciers during this century. This has been determined by taking measurements over time, comparing photographs taken over extended periods of time, and by examining the resulting landforms such as the moraines that have formed far beyond the glaciers in evidence at this point in time.

That does not mean that the Svalbard glaciers will always be retreating. Glacier movement tends to fluctuate between periods where they are advancing and those when they are retreating. The greatest surge of movement known for a Svalbard glacier occurred in 1935-1936 at the Nigribreen glacier. It moved more than 12 kilometers during the year, meaning it moved about 35 meters per day, on average, sometimes at far greater speeds on a day-to-day basis!

A glacier moves as a solid. The center of the glacier moves more rapidly than the sides and the surface moves more rapidly than the bottom. This is largely due to the bottom and the sides being held back by friction.

So, Candy, you can imagine that as a glacier moves, its ice and debris sculpt the landscape. Materials are removed from one location and carried to another. In this way, a glacier leaves a mark on the landscape to record its presence.

Thank you for posting your question!