Glacier Terms & Definitions
The zone of accumulation is where the snow is converted from snow to ice.
The area at the foot of the glacier is the zone of ablation; this is where ice will melt, evaporate or calve (which causes icebergs).
If accumulated snow survives a melting season, or warming period, it is called firn.
The equilibrium line is what separates the zone of accumulation and zone of ablation.
Crevasse – fractures near the top of the glacier caused by environmental stress.
The zone of plastic flow describes the fluid ice flow near the bottom of the glacier.
At the base of the glacier, basal slips – when ice slips over the surface – occur.
Glaciers depress the surface because of their weight. Once they melt, the ground rebounds, in a process called postglacial rebound.
Internal deformation occurs when the weight and mass of a glacier causes it to spread out due to gravity.
Glacial surges are when the glaciers will move up to 20 feet over a year. This rate is not typical for glacier flow.
When two alpine glaciers merge together at the base of a mountain it is called a piedmont glacier. If the piedmont flows into the sea, it is called a tidewater glacier.
Valley glaciers are formed in mountain valleys. Cirque glaciers are confined to the valley.
Ice caps glaciers cover mountain tops.
Elongated hills formed by historical glacial action are called eskers.
Moraines are mounds or ridges created by the accumulation of glacial till.
Glaciers are massive bodies of ice that slowly move across the landscape. They form by layers of snow compacted over the years to form a very thick layer of ice. Two primary types of glaciers exist: continental and alpine. Continental glaciers are large, dome-shaped sheets of ice and are vastly spread throughout the land. Alpine glaciers are found in mountain regions and in their valleys.
Under the pressure of its own weight and by the force of gravity, glaciers will flow outwards and downwards like a giant frozen river. These massive pieces of ice have a profound effect on the lay of the land as it moves the earth, breaks down rocks and creates hills. Our own landscape transformed drastically during the last Ice Age. Without this natural phenomenon, Indiana wouldn’t be as unique as it is today.
How Glaciers Shaped Indiana
Around 16,000 years ago glaciers covered Indiana. For hundreds of years, the glaciers moved about a foot a day. While moving outward and then retreating back, the glaciers carved the land. As the ice melted, the glaciers created and left behind dunes, hills, rivers and lakes.
There are basically two types of landscape present in Indiana. In the northern and central parts of the state, the land is flat plains. In the southern region, the landscape is hilly with great stands of forests. It was during the last ice age where these stark differences developed.
Glacial ice extended and retreated several times in the Midwest during the Pleistocene epoch, or the Great Ice Age. Yet every glacier that spread over Indiana never extended past the central region of the state. Once the glaciers melted the dirt, rocks and sand - or glacial till - that were picked up by the ice were all that was left behind. Any hills or valleys created by previous ice ages were filled with this till and left the land flat. Today this central area is known as Tipton Plain Till. In the northern part of the state, where glaciers retreated more quickly, moraines - or glacial till ridges - were left, but was still left relatively level.
Southern Indiana's landscape greatly differs from the rest of the state. As mentioned before, the glaciers of the last ice age did not extend past central Indiana. Instead, floods from the melted ice carved rivers and the hills that this part of the state is known. The melted glacier water also created the karst topography by eroding and shaping the limestone bedrock that was left behinds thousands of years ago. That is why our caves, sinkholes and disappearing streams are found only in the southern parts of the state.
Glaciers not only shaped the landscape of Indiana, but encouraged evolution and adaptations in the flora and fauna that exist in Indiana today. Without glaciers, who knows what Indiana’s landscape would be?
For more information on the geology of our great state, check out the Indiana Geological Survey website.
Importance of Glaciers Today
Glaciers are not a thing of the past. Although they do not cover a third of the Earth’s surface as they did almost 16,000 years ago, glaciers can be found all over the world. In fact, they can be found on every continent – though more common in Arctic locations like Alaska and Antarctica.
Today glaciers cover around 12% of the Earth’s surface and hold almost 75% of our freshwater. According to the National Snow and Ice Data Center, if the glaciers were all to melt, sea levels would rise about 230 feet. Not only would small islands and coastal areas be at risk, but a majority of our freshwater sources would be depleted or lost to salty waters. Since glaciers advance or retreat in response to changes in temperature, they can be sensitive indicators of climate change.
Climate change is a major concern when it comes to glaciers. If the climate continues to warm, then the glaciers will eventually melt away. High greenhouse gas emissions – like carbon dioxide, methane and nitrous oxide – contribute to the overall warming of the climate. These gases are by-products of every day human activities like driving our cars, heating our homes and using electricity produced in coal-burning plants. Deforestation – the mass cutting and burning of forests for agricultural purposes, manufacturing needs or land development – is another cause of global warming because fewer trees means less carbon dioxide conversion to oxygen.
They say that pictures are worth a thousand words. Well, these images may prove just how fast glaciers are melting. In 1940, this photo was taken of the Northwestern Glacier in Kenai Fjords National Park, Alaska.
In 2005, M.F. Bruce visited the Northwestern and captured this photo taken from the same location sixty-five years later.
The differences between these images are staggering. If temperatures continue to rise at the current rate, glaciers will certainly be affected. For example, it has been predicted that all glaciers in Glacier National Park of Montana will have melted away by 2030. Mt. Kilimanjaro, the highest mountain in Africa, has been topped with glaciers for the past 12,000 years. Scientists now believe that the ice cap glaciers will melt entirely by 2020. Therefore it is imperative that we are more aware of climate change and the ways to decrease our emissions of greenhouse gases. Visit the EPA's Climate Control page for tips on What You Can Do.