Glacial Morphology

Glaciers consist of snow that has accumulated year after year. Glaciers have a positive mass balance: The accumulation of precipitation (usually in the form of snow) is greater over a year's time than the melting, leaving the glacier with a net increase in mass. As the snow deposit increases in thickness, the heavy snow burden presses down on the layers of snow accumulated beneath it. The extreme compression forces the snow to recrystallize. The grains of ice become similar in size and shape to table sugar. Over time, the grains grow larger. The pressure forces the air pockets within the mass to shrink. This process increases the ice's density and eventually compresses the lower levels into large, thick ice masses.

After approximately two years, the snow turns into a state called "firn," an intermediate state between snow and glacier ice. As the years pass, the ice crystals become so compressed and dense that any air pockets that are left are minuscule. The ice crystals in extremely old ice can grow to several inches in length. Once the snow undergoes this metamorphosis into ice, a process that can take a century or more, it becomes a glacier. This extreme density and compression is what gives glacial ice its distinctive pale blue color.

Because glaciers are a collection of a formidable, enormous mass of ice, when they form in a canyon on an inclined slope, they have the ability to move. Glaciers can vary in size from small alpine glaciers smaller that a football field to mammoth ones stretching across the terrain for almost 100 miles (160 km).

Glaciers cover roughly 10 percent of Earth's surface. As a testament to the last ice age, most of the world's glaciers are located in the polar environments of Antarctica and Greenland. Each year, these two locations attract research scientists eager to unlock the climatic secrets from the world's past. For instance, the University of Nebraska-Lincoln sent seven people to Antarctica to join a team of world-class international geoscientists for a three-month expedition to investigate the continent's role in global climate change. They are part of the ANDRILL geological drilling project, organized to recover rock-core samples from the McMurdo Sound region to study the history of the Ross Sea area's ice sheets. As the edges of the ice sheet break free and fall into the ocean, it opens the way for the interior glaciers to flow faster toward the edges of the continent.

The USGS is currently involved in mapping the changes in area and volume of the polar ice sheets in both Antarctica and Greenland and relating the impact of recent melting to worldwide rising sea levels. In other studies, NASA is busy measuring the shape of the ice sheets and determining whether they are getting thicker or thinner in different areas and what they may mean for the short- and long-term, such as advancement or retreat. They are trying to model the interior glacial "mass balances."

In Greenland and the Arctic, scientists are also trying to understand the mass balance of glacial ice. Konrad Steffen, a glaciologist from the University of Colorado, has camped on Greenland's ice sheet every year since 1990. His goal is to determine the way that meltwater affects ice movement. He lowered a camera 330 feet (100 m) into an ice crevasse to determine if the huge waterways under the ice could be seen. He discovered that as more water channels through these underground tunnels, the glacier can shift more rapidly.

The U.S. National Science Foundation (NSF) is particularly heavily involved in Greenland and the Greenland Ice Sheet Project Two (GISP2). This scientific endeavor is to understand environmental change in the Arctic in order to help current science better predict future situations and needs. Meanwhile, a new study, led by Son Nghiem of NASA's Jet Propulsion Laboratory, has used buoys and satellite imagery to prove winds since 2000 have pushed huge amounts of thick ice out of the Arctic basin past Greenland.

The National Snow and Ice Data Center at the University of Colorado, funded by NASA, has been involved in monitoring the extent of Arctic sea ice at the end of each summer. Josefino Comiso, who is a senior researcher for NASA's Goddard Space Flight Center announced that the ice is melting at an accelerated rate. The seasons when sea ice melts, between early spring and late fall, have become much longer and warmer each decade.

One of a glacier's unique characteristics is that it can move. Movement occurs as soon as a glacier becomes about 60 feet (18 m) thick. Under the imposing mass of the ice, coupled with Earth's gravity, glaciers move as an extremely slow river of ice. They can move down canyons, across flat areas, and out to sea. According to the climatic conditions, glaciers can rapidly or slowly advance or retreat, providing an indication of climatic trends. Typically, movement occurs over a long period of time, but occasionally, glaciers have been known to surge forward up to 33 feet (10 m) per day over a short interval of time.

Global warming, however, is causing many of Earth's glaciers to retreat. Rapid glacial retreat can be visible over just a few months or years. When glaciers are traveling down mountain canyons, they can join together where canyon junctions merge. As the mass of the glacier grinds over the ground, it breaks up pieces of rock and soil and carries the debris

This mountain glacier is located in the East Coast Mountains of Baffin Island, Nunavut, Canada. This river of ice flows downhill at several feet per year. Glaciers begin in high mountain peaks and flow down steep mountain valleys, where they eventually merge into one another and flow as a giant river of ice, eroding the mountainsides and valley bottom as they grind their way downhill. (John T. Andrews. NOAA Paleoclimatology Program/Department of Commerce; INSTAAR and Department of Geological Sciences, University of Colorado, Boulder)

This mountain glacier is located in the East Coast Mountains of Baffin Island, Nunavut, Canada. This river of ice flows downhill at several feet per year. Glaciers begin in high mountain peaks and flow down steep mountain valleys, where they eventually merge into one another and flow as a giant river of ice, eroding the mountainsides and valley bottom as they grind their way downhill. (John T. Andrews. NOAA Paleoclimatology Program/Department of Commerce; INSTAAR and Department of Geological Sciences, University of Colorado, Boulder)

Tidewater glaciers are the glaciers that calve icebergs into the ocean. They can pose a problem for ships that navigate nearby ocean waters.

along the bottom and sides of the glacier. This debris being carried along takes on a banded appearance running the length of the glacier.

The bulk of the world's glaciers are in Antarctica and Greenland, but they also occur on other continents. Because they must meet specific geographic and physiographic criteria in order to survive, they only occur in specific areas. Glaciers form above the snow line on mountains because these are areas that receive large amounts of snowfall during the winter season and experience cool temperatures in the summer. These conditions must exist so that the snow and ice do not melt from one season to another.

There are several types of glaciers: mountain glaciers, hanging glaciers, piedmont glaciers, tidewater glaciers, cirque glaciers, and valley glaciers. Mountain glaciers are those that develop high in mountainous areas. They can occupy a single mountain peak or be spread across an

Types of Glaciers

GLACIER TYPE

CHARACTERISTICS

Hanging glacier

• Attached to steep mountainsides

• Looks wider than they are long

• Forms in steep, mountainous areas, such as the Alps in Europe

Piedmont glacier

• Forms when a steep valley glacier flows out onto a broad, flat area where it spreads out into a wide fan shape

Tidewater glacier

• Flows across land until it reaches the ocean

• Calves icebergs that are common in Arctic waters

Cirque glacier

• Forms in a bowl-shaped hollow on a mountainside

Valley glacier

• Originates from mountain glaciers that flow downhill and are channeled into valleys

• Can extend for many miles

• Often flows far enough to reach coastal areas, where it empties into the ocean

entire mountain range. The most common areas to find mountain glaciers are in the Arctic regions of Canada and Alaska, the Himalayas in Asia, the Alps in Europe, Antarctica, and the Andes in South America.

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