The name Glacier is derived from small formations of ice and snow that are isolated in mountain valleys as well as extensive Ice Sheets that cover Antarctica. Mid-size formations are named Ice Fields and Ice Caps. Today, glaciers cover approximately 10% of the total surface of the earth. At their greatest development during the reoccurring ice ages, glaciers covered 30% or more of the surface of the earth. Current day glaciers contain about 80% of the fresh water on earth. Today the areas of the world where we can view and study glaciers represent some of the greatest natural beauty on earth and remain an important part of the ecosystem of earth. The geological impact that glaciers have played during reoccurring ice ages provide important clues in understanding the shape and character of our landscape.
Presently the king of all Ice Sheets is the 5 million square mile, 14,000-foot thick, formation that covers Antarctica. This large mass does move and flow by the force of gravity until it reaches the ocean where it breaks up to form icebergs.
Ice Caps are similar to Ice Fields but are much smaller due to the fact that they develop in a contained area such as a mountain basin. This type of formation can be seen in many areas of northern Canada and Alaska.
Ice Fields form in mountainous regions when numerous separate glaciers connect to form a field. One distinction between a Sheet and a Field is the fact that fields form in areas where the separate glaciers connect. In the low valleys, ice fields are not high enough to cover the mountain peaks, which protrude above the ice and snow of the glacier. Sheets cover all the landmass. Large Ice Fields can be found in Alaska.
Aside from these large formations, separate smaller single glaciers can form in any region that is cold enough for a portion of the year. It must receive sufficient snowfall to accumulate beyond the subsequent melting that will occur during seasonal warming. If the conditions are proper, the snow that accumulates turns into ice as it compresses under more and more weight from successive snowfall.
Glaciers can form in mountain valleys if they are at the end of a flowing Ice Cap or they can form on their own as ice and snow accumulate and flow down the Valley. This type of formation is known as a Valley Glacier. If a mountain range contains a number of Valley Glaciers that flow together, the accumulations at the base can form a larger flatter formation known as a Piedmont Glacier.
Another type of glacier, the Alpine Glacier, is different from the Valley Glacier as it forms in basins or bowls and, if it grows large enough, flows over the edge of the basin and break up as it falls.
Glaciers can have a dramatic affect on the terrain they cover. In the last Ice Age much of North America was covered in ice and snow. One interesting result of the accumulation of weight is the resulting compression of the land under the glacier. Portions of Northern Europe and North America are still rebounding from the weight that was removed as the glaciers retreated as the climate warmed. The cycle of Ice Age formation is thought to be roughly on the order of every 100,000 years and the last Ice Age was at its peak approximately 18,000 years ago.
The last Ice Age impacted the geology of North America and also had influence on early man and other animals that lived on the land. During the height of the Ice Age much water was trapped in the Ice Fields. As the ice melted it caused the sea level to rise thus flooding much of the coastal areas. This rise in sea level also changed migration patterns in parts of the earth like the Bering Sea thus disrupting new migration from Europe to North America.
The advance and retreat of Glaciers and the constant down slope movement also has tremendous influence on the land. Erosion from the grinding pressure and erosion from the glaciers water flow dramatically shaped mountain valleys. Rock material removed from one area was deposited in another. Mountain tops that remain above the glacier are formed into sharply defined peaks commonly know as horns. As glaciers erode surface material down to the bedrock, deep grooves are worn into the bedrock from the boulders that the glacier carries along. Large deposits of stone, sand and soil are deposited near the outermost edge of glaciers and are referred to as Drumlins. Water trapped behind retreating layers of ice from glaciers form interesting terraces as they deposit remaining material. Isolated blocks of ice from retreating glaciers can melt slowly to form depressions called kettle holes.
Much of the beauty and varied terrain that we enjoy here in the Green Mountains of Vermont can be directly related to glaciations.
Today, scientists study glaciers in order to learn about the past. Layers of ice in glaciers hold clues to the past as they hold evidence of the atmosphere, weather, and geology of the age they represent. Glaciers also are helpful to scientists as they look for clues as to current trends and patterns in weather. Glaciers are sensitive to climate change and thus provide a tool to help us learn about the effects of global warming, solar influence and weather trends.