Glacier BasicsA glacier is essentially a huge mass of ice resting on land or floating in the sea next to land. Moving extremely slowly, a glacier acts similarly to an immense river of ice, often merging with other glaciers in a stream-like manner.
Regions with continuous snowfall and constant freezing temperatures foster the development of these frozen rivers. It is so cold in these regions that when a snowflake hits the ground it does not melt, but instead combines with other snowflakes to form larger grains of ice. As more and more snow accumulates, mounting weight and pressure squeeze these grains of ice together to form a glacier.
A glacier cannot form unless is it above the snowline, the lowest elevation at which snow can survive year round. Most glaciers form in high mountain regions such as the Himalayas of Southern Asia or the Alps of Western Europe where regular snow and extremely cold temperatures are present. Glaciers are also found in Antarctica, Greenland, Iceland, Canada, Alaska, and even South America (the Andes), California (the Sierra Nevada), and Mount Kilimanjaro in Tanzania.
As tiny air bubbles are eventually forced out by the increasing pressure the glacier appears blue, a sign of highly dense, airless ice.
Glaciers may be retreating worldwide due to global warming, but they still cover about 10% of earth’s land and hold about 77% of earth's freshwater (29,180,000 cubic kilometers ).
Types of GlaciersGlaciers can be characterized in two ways based on their formation: alpine and continental.
Alpine Glacier - Most glaciers that form in a mountain are known as alpine glaciers. There are several subtypes of alpine glaciers:
- Cirque: a cirque is a bowl shaped hollow at the head of a valley. Within a cirque lies a snowfield, the place where snow accumulates to form a cirque glacier.
- Valley: any glacier that resides in an area eroded by stream action is called a valley glacier. These types of glaciers tend to be very long and often times pass below the snowline.
- Piedmont: when multiple valley glaciers come together as one at a large stretch of flat line, the resulting mass is a piedmont glacier.
- Tidewater: a glacier that meets the sea is known as a tidewater glacier. Usually a process called calving occurs, when a piece of the glacier breaks off in to the sea, forming a large mass of floating ice known as an iceberg.
Continental Glacier – An expansive, continuous mass of ice considerably bigger than an alpine glacier is known as a continental glacier. There are three primary subtypes:
- Ice Sheet: the largest of any glacier type, extending over 50,000 square kilometers. The only places on earth that have these frozen monsters are Antarctica and Greenland. Antarctica alone is home to 92% of all glacial ice worldwide. Ice sheets are so massive and heavy that they literally bend the continental crust on which they sit, a phenomena known as isostatic depression.
- Ice Cap: similar to an ice sheet, though smaller and forming a roughly circular, dome-like structure that completely blankets the landscape underneath.
- Ice Field: a smaller version on an ice cap that fails to cover the land and is elongated relative to the underlying topography.
Glacial MovementThere are two types of glacial movement: sliders and creepers. Sliders travel along a thin film of water located on the bottom of the glacier. Creepers, on the other hand, form internal layers of ice crystals that move past one another based on the surrounding conditions (e.g. weight, pressure, temperature). The top and middle layers of a glacier tend to move faster than the rest. Most glaciers are both creepers and sliders, plodding along in both fashions.
Glacier speed can vary from virtually at rest to a kilometer or more per year. On average, though, glaciers move at the laggardly pace of a couple hundred feet per year. In general, a heavier glacier moves quicker than a lighter one, a steep glacier quicker than a less steep one, a warmer glacier quicker than a cooler one.
Glaciers Shaping the LandBecause glaciers are so massive, the land they dominate is carved and shaped in significant and long lasting ways through glacial erosion. As a glacier moves it grinds, crushes, and envelopes rocks of all shapes and sizes, wielding the ability to alter any landform in its path, a process known as abrasion.
A simple analogy when thinking about how glaciers shape the land is to envision the large rocks it carries as chisels, gashing and scraping out new formations in the ground below.
Typical formations that result from the passing of a glacier include U-shape valleys (sometimes forming fjords when the sea fills them), long oval hills called drumlins, narrow ridges of sand and gravel called eskers, and hanging waterfalls, among many others.
The most common landform left by a glacier is known as a moraine. There are a variety of these depositional hills, but all are characterized by unstratified (a fancy word for unorganized) material including boulders, gravel, sand, and clay.
Why are Glaciers Important?Glaciers have shaped much of the earth as we know it through the processes described above and are just as intimately connected with the earth's current condition.
The common fear is that with temperatures rising worldwide, glaciers will begin to melt, releasing some or all of the huge amounts of water held inside. As a result, the oceanic processes and structures we have adapted to will abruptly change, with unknown consequences.
To find out more, scientists are turning to paleoclimatology, a field of study that uses glacial deposits, fossils, and sediments to determine the history of earth's climate. Ice cores from Greenland and Antarctica are currently being used to this end.