A glacier is a solid mass of ice formed over thousands of years. In contrast, rivers are liquid water flowing downhill. However, glaciers are not always solid. Some glaciers are composed of loose rock fragments called moraines. These rocks form where the glacier erodes the bedrock. When the glacier melts, the rocks fall out of the ice and become debris. Other glaciers consist entirely of ice.
The process of moving a glacier begins with precipitation falling as rain or snow. As the moisture freezes, it becomes ice. Ice is heavier than air, so it stays close to the ground. Over time, the weight of the ice causes it to push up against the surface of the earth. Eventually, the pressure builds up enough to force the ice outward. This movement creates a depression in the landscape. If there is no resistance, such as another mountain range, the glacier continues to spread.
As a glacier spreads, it forms a ridge along the side of the valley. This ridge is called a terminal moraine. Terminal moraines are often visible because they are usually covered with grass and shrubs. Sometimes, however, the glacier pushes far beyond the end of the valley and leaves behind a massive pile of ice called a lateral moraine. Lateral moraines are much less common than terminal moraines. They tend to occur near lakes or streams.
Once the glacier reaches the bottom of the valley, it starts to melt. Water seeps into cracks in the ice and escapes through fissures. Because water is lighter than ice, it floats upward, causing the ice to flow toward areas of low elevation. This is why glaciers flow uphill.
When the glacier stops melting, it can continue to flow even though it is surrounded by mountains. This happens because the ice is still under pressure from above. When the pressure is removed, the glacier slows down.
Glacier Advance and Retreat
The term “glacial advance” refers to the growing mass of land covered by glaciers. Glaciers grow when snow and ice accumulate on the surface of a glacier. As the accumulation continues, the weight of the ice causes it to compress into layers. When enough pressure builds up, the ice becomes denser than the surrounding rock and sinks down beneath the surface.
A glacier advances when snow and ice are added to the bottom of the glacier. A glacier retreats when snow and ice melt off the bottom of the glacier and flow away.
Motion and Movement
A glacier is a massive body of snow and ice that forms over thousands of years. A glacier is usually composed of three layers: the bottom layer is the firn; the middle layer is the silt; and the uppermost layer is the ice. As glaciers flow downhill, they are constantly gaining and losing ice. This process is known as glacial motion.
Glacier movement occurs because the weight of the ice above causes it to deform downward into the underlying rock. When the glacier reaches the bedrock, the weight of the ice becomes too great and the glacier begins to slide toward lower ground. In some cases, the ice may even detach from the bedrock and float away.
Revealed by Satellite Radar
Glaciers are massive bodies of frozen water that flow down mountain slopes over thousands of miles. They cover nearly half of Earth’s landmass. Glaciers move slowly, forming and eroding mountain ranges. But sometimes, they move much faster. When that happens, it causes avalanches and floods downstream. This process is called glacial outburst flood.
The most famous example of a glacial outburst flood is the one that occurred in 1910 near Valdez, Alaska. A huge chunk of ice broke off Mount Logan, slid into the town, and caused $30 million worth of damage. Scientists use satellites to watch glaciers like never before. By watching the movement of the ice, scientists can see what is happening beneath the surface.
They do this by flying above the glaciers with radar satellites. As the radar waves pass over the ice, they bounce back to earth. From those reflections, scientists can determine whether the ice is moving up or down.
In addition to measuring the speed of the ice, scientists also look at the colors of the reflected signal. In some cases, the color pattern represents the height of the glacier. Other times, the color pattern represents how quickly the ice is flowing.
By combining both types of data, scientists can make a 3D model of the glacier. Then they overlay maps of elevation and velocity onto the model. This allows them to see exactly where the ice is moving and how fast it is moving.
Why do some glaciers melt faster than others?
Dr Ellyn Enderlin, assistant professor of geophysics at Boise State Univeristy, studies the impact of glacier retreat on our climate and environment. She says that while many people think of glaciers as frozen mountains, they actually consist mostly of liquid water. Because of this, she explains that there are three main factors influencing the speed at which glaciers melt:
2. Water pressure
She says that temperature plays a big role because warmer air temperatures cause snow to melt faster. However, she adds that the effect isn’t linear; the amount of heat energy absorbed by each gram of snow increases exponentially with increasing temperature. This means that even small changes in temperature can lead to significant differences in melting rates.
Water pressure also affects glacier melting. When water flows over a surface, it exerts a force called hydrostatic pressure. If you imagine a column of water sitting on top of a flat surface, like a sheet of paper, then the weight of the column above it creates a downward force. In the same way, water flowing over a mountain exerts a greater downward force as it moves downslope. So, the deeper the water travels into the glacier, the stronger the downward force becomes and the easier it is for the glacier to break apart.
Snowfall also impacts melting rates. A thick layer of snow acts as insulation, keeping the ice underneath cool. But as snow accumulates, it insulates less and less, meaning that the ice beneath gets hotter. And once the base of the glacier reaches a certain depth, it starts to melt.