Glaciers are large masses of moving ice that are often called rivers of ice. They form slowly and some take hundreds and perhaps thousands of years to reach their maximum size. Glaciers form because the annual snowfall in an area does not melt completely in the summer, and accumulates over time. As the snow accumulates, it slowly compresses under its own weight into a huge mass of ice. When a glaciers size reaches about 18 meters thick, its weight and the pull of gravity cause it to move slowly over land changing the lands surface features. Valley glaciers are found on land that slopes and flow downhill, while continental glaciers are on flat land and move out from their edges.
are usually found at higher elevations and latitudes. They are found
areas, on islands, near the equator, and along some coastlines. Glaciers
can become natural hazards if they melt during the warmer season and
cause flooding in surrounding areas. Glaciers cut into headwalls and
valley walls making the slopes unstable, often resulting in rockslides.
On unusually hot or rainy days, cavities within the glacier may suddenly
release water, causing glacial outburst floods. Outburst floods often
roar rapidly along carrying rocks and debris (debris flow) and
may suddenly and without warning cause a rapid rise in water level in
Tidal glaciers along coastlines can break off into icebergs during a process called calving. Often massive in size, icebergs can float into shipping channels and endanger ships. The U.S. Coast Guard has, since 1913, worked with the International Ice Patrol to monitor iceberg danger in the North Atlantic Ocean. The dangerous mix of icebergs, fog, severe storms, fishing vessels and busy trans-Atlantic shipping lanes could result in tragedy. The Titanic disaster in 1912, which resulted in 1517 deaths, and the loss of the S.S. Hanshedtoft in 1959 are proof of the danger of icebergs.
Since 1974, scientists at the Vostok Station in Russia have examined ice core samples from Antarctica. Scientists have identified trapped bacteria, fungi, pollen grains, and algae that are almost 4,000 years old. Glaciers have also preserved fossil remains, such as those of whales, in the state of Maine. The 5,000-year-old “ice man” found in the Austrian/Italian Alps and a 550-year-old Canadian are providing information about human evolutionary and cultural history.
Throughout the history of the Earth glaciers have increased and decreased in size. Analyzing glacial changes helps us better understand the complex relationships between climate, the environment, and living things.