Glaciers and Ice Sheets

Glaciers and Ice Sheets

Glaciers are made up of fallen snow that, over many years, compresses into large, thickened ice masses. Glaciers form when snow remains in one location long enough to transform into ice. What makes glaciers unique is their ability to move. Due to sheer mass, glaciers flow like very slow rivers. Some glaciers are as small as football fields, while others grow to be over a hundred kilometers long.

Presently, glaciers occupy about 10 percent of the world's total land area, with most located in polar regions like Antarctica and Greenland. Glaciers can be thought as remnants from the last Ice Age, when ice covered nearly 32 percent of the land, and 30 percent of the oceans. An Ice Age occurs when cool temperature endure for extended periods of time, allowing polar ice to advance into lower latitudes. For example, during the last Ice Age, giant glacial ice sheets extended from the poles to cover most of Canada, all of New England, much of the upper Midwest, large areas of Alaska, most of Greenland, Iceland, Svalbard and other arctic islands, Scandinavia, much of Great Britain and Ireland, and the northwestern part of the former Soviet Union.

Within the past 750,000 years, scientists know that there have been eight Ice Age cycles, separated by warmer periods called interglacial periods.

Presently, 10% of land area is covered with glaciers.
Glaciers store about 75% of the world's freshwater.
Glacierized areas cover over 15,000,000 square kilometers.
Antarctic ice is over 4,200 meters thick in some areas.
In the United States, glaciers cover over 75,000 square kilometers, with most of the glaciers located in Alaska.
During the last Ice Age, glaciers covered 32% of the total land area.
If all land ice melted, sea level would rise approximately 70 meters worldwide.
Glacier ice crystals can grow to be as large as baseballs.
The land underneath parts of the West Antarctic Ice Sheet may be up to 2.5 kilometers below sea level, due to the weight of the ice.
North America's longest glacier is the Bering Glacier in Alaska, measuring 204 kilometers long.
Glacial ice often appears blue when it has become very dense. Years of compression gradually make the ice denser over time, forcing out the tiny air pockets between crystals. When glacier ice becomes extremely dense, the ice absorbs all other colors in the spectrum and reflects primarily blue, which is what we see. When glacier ice is white, that usually means that there are many tiny air bubbles still in the ice.
The Kutiah Glacier in Pakistan holds the record for the fastest glacial surge. In 1953, it raced more than 12 kilometers in three months, averaging about 112 meters per day.
In Washington state alone, glaciers provide 470 billion gallons of water each summer.
Antarctic ice shelves may calve icebergs that are over 80 kilometers long.
Almost 90% of an iceberg is below water--only about 10% shows above water.
The Antarctic ice sheet has been in existence for at least 40 million years.
From the 17th century to the late 19th century, the world experienced a "Little Ice Age," when temperatures were consistently cool enough for significant glacier advances.

Ice sheets and glaciers form the largest component of perennial ice on Earth. Over 75% of the world's fresh water is presently locked up in these frozen reservoirs.

A Glacier is any large mass of perennial ice that originates on land by the recrystallization of snow or other forms of solid precipitation and that shows evidence of past or present flow. A glacier occupying an extensive tract of relatively level land and exhibiting flow from the center outward is commonly called an ice sheet. Glaciers form when snow accumulates on a patch of land over tens to hundreds of years. The snow eventually becomes so thick that it collapses under its own weight and forms dense glacial ice. When enough of the ice is compacted together it succumbs to gravity and begins to flow downhill or spread out across flat lands. What makes glaciers unique is their ability to move. Due to sheer mass, glaciers flow like very slow rivers.

More than 90 percent of the 33 million cubic kilometers of glacier ice in the world is locked up in the gigantic Greenland and Antarctic ice sheets.

NASA: A Short Tour of the Cryosphere Video

Most of the world's glaciers are found near the Poles, but glaciers exist on all of the world's continents, even Africa. Australia doesn't have any glaciers; however, it is considered part of Oceania, which includes several Pacific island chains and the large islands of Papua New Guinea and New Zealand. Both of these islands have glaciers.

Glaciers require very specific climatic conditions. Most are found in regions of high snowfall in winter and cool temperatures in summer. These conditions ensure that the snow that accumulates in the winter isn't lost (by melt, evaporation, or calving) during the summer. Such conditions typically prevail in polar and high alpine regions. There are two main types of glaciers: valley glaciers and continental glaciers (known as ice sheets).

The amount of precipitation (whether in the form of snowfall, freezing rain, avalanches, or wind-drifted snow) is important to glacier survival. In areas such as Antarctica, where the low temperatures are ideal for glacier growth, very low annual precipitation causes the glaciers to grow very slowly.

Motion and change define a glacier's life. Glacial ice advances, then retreats. Glaciers grow and shrink in response to changing climate.

The ice cover in Greenland and Antarctica has two components – thick, grounded, inland ice that rests on a more or less solid bed, and thinner floating ice shelves and glacier tongues. An ice sheet is actually a giant glacier, and like most glaciers it is nourished by the continual accumulation of snow on its surface. As successive layers of snow build up, the layers beneath are gradually compressed into solid ice. Snow input is balanced by glacial outflow, so the height of the ice sheet stays approximately constant through time. The ice is driven by gravity to slide and to flow downhill from the highest points of the interior to the coast. There it either melts or is carried away as icebergs which also eventually melt, thus returning the water to the ocean whence it came. Outflow from the inland ice is organized into a series of drainage basins separated by ice divides that concentrate the flow of ice into either narrow mountain-bounded outlet glaciers or fast-moving ice streams surrounded by slow-moving ice rather than rock walls. In Antarctica much of this flowing ice has reached the coast and has spread over the surface of the ocean to form ice shelves that are floating on the sea but are attached to ice on land. There are ice shelves along more than half of Antarctica’s coast, but very few in Greenland.

Credit:Hugo Ahlenius, UNEP/GRID-Arendal based on material provided by K. Steffen, CIRES/Univ. of Colorado

NASA JPL Video: The Big Thaw October 01, 2007 A thick chunk of Arctic sea ice the size of two states has disappeared. Is it global warming or normal causes? A new NASA-led study found a 23-percent loss in the extent of the Arctic's thick, year-round sea ice cover during the past two winters. Between winter 2005 and winter 2007, the perennial ice shrunk by an area the size of Texas and California combined. This drastic reduction of perennial winter sea ice is the primary cause of the fastest-ever sea ice retreat on record this summer. Scientists say the rapid decline in winter perennial ice was caused by unusual winds. For more information go to: www.jpl.nasa.gov

Ice Sheets

Greenland

Credit:NASA

Greenland

Found only in Antarctica and Greenland, ice sheets are enormous masses of glacial ice and snow expanding over 50,000 square kilometers. The ice sheet on Antarctica is over 4200 meters thick in some areas, covering nearly all of the land features except the Transantarctic Mountains, which protrude above the ice.

Antarctica

According to the National Snow and Ice Data Center, the Northern Hemisphere sea ice extent, which is measured from passive microwave instruments onboard NOAA satellites, was 5.9 million square kilometers as of September 14, 2006, the second lowest on record (image to the left). This is the fifth consecutive year September sea ice extent has been below the long-term (1978-2000) mean. The September rate of sea ice decline is now almost 9 percent per decade (60,421 square kilometers per year).

Ice Shelves

Larsen Ice Shelf, Antarctica

Landsat 7 Science Team and NASA GSFC Satellite: Landsat 7 Sensor: ETM+

Ice shelves occur when ice sheets extend over the sea, floating on the water. In thickness they range from a few hundred meters to over 1000 meters. Ice shelves surround nearly all of the Antarctic continent. Retreating ice shelves may provide indications of climate change.

Credit:Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Ice Caps

Ice caps are miniature ice sheets. An ice cap covers less than 50,000 square kilometers. They form primarily in polar and sub-polar regions that are relatively flat and high in elevation.

Mountain Glaciers

Glacier Peak North Cascade Mountains

USGS Photograph

These glaciers develop in high mountainous regions, often flowing out of icefields that span several peaks or even a mountain range. The largest mountain glaciers are found in Arctic Canada, Alaska, the Andes in South America, the Himalayas in Asia, and on Antarctica.

Valley Glaciers

Commonly originating from mountain glaciers or ice fields, these glaciers spill down valleys, looking much like giant tongues. Valley glaciers may be very long, often flowing down beyond the snow line, sometimes reaching sea level.

Piedmont Glaciers

Malaspina Glacier

NASA Space Shuttle Photograph

Piedmont glaciers occur when steep valley glaciers spill into relatively flat plains, where they spread out into bulb-like lobes. The Malaspina Glacier in Alaska, covering over 5,000 square kilometers is one of the most famous examples of this type of glacier.

Cirque Glaciers

Glacier National Park

Cirque Glaciers are named for the bowl-like hollows they occupy, which are called cirques. Typically, they are found high on mountainsides and tend to be wide rather than long.

Hanging Glaciers

Also called ice aprons, these glaciers cling to steep mountainsides. Like cirque glaciers, they are wider than they are long. Hanging glaciers are common in the Alps, where they often cause avalanches due to the steep inclines they occupy.

Tidewater Glaciers

Glacier Bay Alaska

As the name implies, these are valley glaciers that flow far enough to reach out into the sea. Tidewater glaciers are responsible for calving numerous small icebergs, while not as imposing as Antarctic icebergs, can still pose problems for shipping lanes.

Greenland

Credit: NASA GSFC Scientific Visualization Studio Data Source: Airborne Topographic Mapper

A NASA study of Greenland’s ice sheet reveals that it is rapidly thinning. In an article published in the Magazine Science, Bill Krabill, project scientist at the NASA Goddard Space Flight Center’s Wallops Flight Facility, Wallops Island, VA, reports that the frozen area around Greenland is thinning, in some places, at a rate of more than three feet per year. Any change is important since a smaller ice sheet could result in higher sea levels. “A conservative estimate, based on our data, indicates a net loss of approximately 51 cubic kilometers of ice per year from the entire ice sheet, sufficient to raise global sea level by 0.005 inches per year, or approximately seven percent of the observed rise,” Krabill said. “This amount of sea level rise does not threaten coastal regions, but these results provide evidence that the margins of the ice sheet are in a process of change,” Krabill said. “The thinning cannot be accounted for by increased melting alone. It appears that ice must be flowing more quickly into the sea through glaciers.”

Polar ice reflects a great deal of the Sun's energy that falls on it back into space, helping regulate the amount of energy arriving on Earth, which drives weather and all the other atmospheric activities. Even a few percent more acres of open water absorbing energy could tip the scales of Earth's energy balance, adding more energy to the atmosphere, altering short- and long-term weather patterns.

Global Warming And The Gulf Stream-Click Here
The Arctic-Click Here
Antarctica-Click Here
Climate Change-Click Here
Global Warming-Click Here

Antarctic Ice Shelf Disintegration Underscores a Warming World-Click Here
Antarctic Ice Sheet's Hidden Lakes Speed Ice Flow Into Ocean, May Disrupt Climate-Click Here
Ice shelf breaks free in Canadian Arctic-Click Here
Polar ice sheet shrinking at alarming rate-click here
2002 Larsen B Ice Shelf Collapses in Antarctica-Click Here
ICE CAPS IN AFRICA, TROPICAL SOUTH AMERICA LIKELY TO DISAPPEAR WITHIN 15 YEARS-click here

Credit: NASA , UNEP, NSIDC,USGS