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Glaciers are flowing masses of ice, created by years of snowfall and cold temperatures. Approximately one-tenth of Earth is covered by glaciers, including Antarctica and parts of Greenland, Iceland, Canada, Russia, and Alaska. Mountainous regions on every continent except Australia also contain glaciers. Glaciers have enormous powers to reshape the face of Earth. Even today, glaciers are altering how our planet looks, and they hold clues to its past and future.
How glaciers form
Glaciers are created in areas where the air temperature never gets warm enough to completely melt snow. After a snowfall, some or most of the snow may melt when it comes into contact with warmer ground temperatures. As the air temperature drops, the melted snow refreezes, turning into small ice granules called firn or névé (pronounced nay-VAY). As additional layers of snow accumulate on top, the firn underneath is compacted. When the accumulation reaches about 150 feet (46 meters) deep, the weight and pressure cause the lower layers to recrystallize into solid ice. As years pass, snow accumulates and the slab of ice grows steadily thicker. Eventually the mound of ice becomes too massive to sit still, and gravity pulls the ice downhill. Once the ice begins to move, it is considered a glacier.
Types of glaciers
Glaciers that flow down a valley from high mountainous regions usually follow paths originally formed by rivers of snowmelt in the spring and summer. These valley or mountain glaciers end in a valley or ocean, and tend to increase the sharpness and steepness of the surrounding mountains along the way. In the Alps, a mountain system in south-central Europe, there are more than 1,200 valley glaciers.
Piedmont glaciers are large, gently sloping ice mounds. Also known as lakes of ice, piedmont glaciers form when a valley glacier reaches the lowlands or plain at the foot of a mountain and spreads out. These are common in Alaska, Greenland, Iceland, and Antarctica.
Glaciers that form in small valleys on the sides of mountains are called ice caps. Found in Norway, Iceland, Greenland, and Antarctica, ice caps usually do not move out of their basinlike area.
The largest form of glacier is called a continental glacier, a huge ice sheet that moves slowly outward from its center. Ice sheets may cover hundreds of thousands of square miles, and are so heavy that they cause the rock underneath to compress into Earth. The largest continental glacier is found on Antarctica, where the ice is more than 2.5 miles (4 kilometers) thick at its center, and hides entire mountain ranges beneath its surface. It extends more than 5 million square miles (12.9 million square kilometers). The Antarctic ice sheet accounts for 90 percent of all the ice in the world, and contains more water than all of Earth's rivers and lakes put together.
Words to Know
Continental glacier: The largest form of and slowest moving glacier, covering large expanses of a continent.
Glacial till: Rock and soil scoured from Earth and transported by a glacier, then deposited along its sides or at its end.
Greenhouse effect: The warming of Earth's atmosphere due to water vapor, carbon dioxide, and other gases in the atmosphere that trap heat radiated from Earth's surface.
Ice age: Period of glacial advance.
Ice caps: Smaller glaciers that form in basinlike depressions in a mountain.
Kettle lakes: Bowl-shaped lakes created by large ice blocks, which formed depressions in Earth's surface.
Meltwater: Melted ice in the glacier's bottom layer, caused by heat that develops as a result of friction with Earth's surface.
Moraines: Large deposits of glacial till that form hills.
Piedmont glacier: Large, gently sloping glaciers found at the foot of mountains, which are fed by alpine glaciers.
Surging: A sudden increase in a glacier's movement as a result of meltwater underneath decreasing its friction.
Valley glacier: Glacier that forms at a high elevation in a mountain region and flows downhill through valleys originally created by rivers.
Glaciers' effects
Most glaciers that exist today are remnants of the last glacial period from 1,800,000 to 11,000 years ago. As glaciers advance and retreat, they plow through rock, soil, and vegetation like a huge bulldozer, altering everything they come into contact with. Ice acts like an adhesive, scooping up rocks and soil that add to the glacier's tremendous powers of erosion.
Thus, a river valley that was once V-shaped becomes U-shaped; the rocks and soil carried with the glacier, known as glacial till, are deposited in huge mounds along the sides and at the end of the glacier, creating entirely new hills, or moraines. Chunks of ice buried in this till create large depressions that later became what are known as kettle lakes.
Glaciers also scour the land to great depths, creating larger lakes such as the North American Great Lakes. During the last ice age, Earth's surface was depressed due to the weight of the glaciers. As the glaciers retreated, Earth's crust rose upward like a sponge. This crustal rebounding, as it is called, is still occurring at slow rates in parts of North America and Europe.
The valley that Eagle River flows and the place where you are standing was formed as Eagle Glacier retreats up the valley. About 3000 years ago this Valley was covered by Eagle Glacier. Over the years the glacier has retreated and formed the valley that we see today.
To claim credit, email the answers to the questions below to the owner of this cache at the link above.
1. How far up the valley does the snout of Eagle Glacier lie from the coordinates given?
2. What type of glacier is Eagle Glacier?
3. Estimate the width of the valley created by the retreat of Eagle Glacier.
A picture of yourself can no longer be required, but they are much appreciated and always nice to look at with the beautiful scenery. If you choose to take a picture, please don’t allow anyone to get the answers to the questions in your photo.
The sign you want is on Rodak trail. The sign will be obvious since they both share the same name.
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