Icebergs and Glaciers

Factors involved: Geography, geological forces, gravitational forces, ice, snow, temperature, weather conditions, wind

Regions affected: Coasts, forests, lakes, mountains, oceans, rivers, towns, valleys

Definition

Glaciers are gigantic ice masses flowing down and over land, whereas icebergs, which originate from glaciers, are ice masses that typically float in oceans. Over the centuries, glaciers and especially icebergs have caused much destruction of human property and lives.

Science

Glaciers, which cover about 10 percent of the earth’s surface, are large masses of freshwater ice formed by the compacting and recrystallization of snow in polar regions and in other regions’ high mountains. When the aggregated ice is large and thick enough, it generally starts flowing downhill by gravity and spreading outward because of its increasing volume. Moving glaciers may terminate on land, where their melting ice turns into a river of water, or they may end in a lake or ocean. Various scientists estimate the number of glaciers at 70,000 to 200,000, depending on how their sizes are defined. Glaciers can vary from an area of about one-third of a square mile to nearly 5 million square miles (12.5 million square kilometers), the size of the great Antarctic ice sheet. About three-quarters of the world’s freshwater exists as glacial ice.

Climate and topography cause differences in a glacier’s size, shape, and physical characteristics. When an ice mass grows so large that it covers an area of about 19,300 square miles (50,000 square kilometers), glaciologists call it an ice sheet, and it usually spreads over vast plateaus, flowing from its center outward. The Antarctic and Greenland ice sheets are the only ones now existing, but during the ice ages of the Pleistocene epoch (1.8 million to 10,000 years ago) ice sheets covered the northern parts of Europe and North America.

If the area covered is less than 19,300 square miles, the glacier is called an ice cap, a flattened, dome-shaped glacier covering both mountains and valleys. In Arctic regions ice caps occur at fairly low altitudes, whereas in such temperate regions as Iceland they occur on high plateaus. In valley glaciers, the flow of ice is confined between a valley’s hillsides or mountainsides. These glaciers may originate from ice sheets or ice caps, but they may also flow out of cirque glaciers nestled in the steep-walled hollows of mountain flanks.

Because a glacier is essentially a flowing ice river, it has a tendency to move from its initial high altitude toward sea level. When glaciers are unconfined by geological barriers, they are able to flow to the sea, where, because of erosive action of changing tides and winds, large chunks of ice split from glacial tongues and ice shelves. These floating masses of freshwater ice are called icebergs, and calving is the process of making them by fracture from a glacier’s seaward end. Icebergs can be white, blue, green, or even black (from the rock materials they contain).

Scientists have categorized icebergs by their sizes and shapes. Tabular (table-shaped) icebergs, also called “ice islands,” are large blocks of ice that protrude several feet above sea level and average 1,640 feet (500 meters) in diameter. Tabular icebergs are rare in the Arctic but common in the Antarctic. Pinnacled icebergs, also called castellated after their castlelike shape, are characteristic of northern polar oceans. Whether tabular or pinnacled, an iceberg has only one-ninth of its mass projecting above the water’s surface, though the ratio of an iceberg’s vertical height above water to its height below varies because of icebergs’ irregular shapes.

Icebergs form mostly during the spring and summer, when warm weather increases the rate of calving. In the Northern Hemisphere glaciers in west Greenland produce about ten thousand icebergs. An average Greenland-born iceberg weighs approximately 2 billion pounds (1 million metric tons) and lasts from two to five years. The West Greenland Current carries these icebergs northward and westward, until eventually many of them are captured by the cold Labrador Current as it moves south to encounter the warm Gulf Stream. They then drift into the region of the Grand Banks, a submarine plateau extending from the Newfoundland coast. Canadian scientists have found a nearly linear decrease in the numbers of icebergs as they wander from northern to southern latitudes. Nevertheless, sufficient numbers survive to populate the North Atlantic shipping lanes with potential hazards to navigation.

Geography

Glaciers develop in geographical regions of the earth where such precipitation as snow and hail exceeds the aggregated frozen precipitation that melts during the summer. This growing glacial accumulation occurs in polar regions where summers are cool and short, but glaciers are also found in temperate zones on high mountains, such as the Alps in Switzerland, and even in the tropics on very high mountains, such as Mount Kilimanjaro in Tanzania. Glaciers occur on all the earth’s continents, except Australia, and on all the world’s great mountain ranges. Whether a glacier develops in a certain geographical region depends on both its latitude and its altitude. Approximately 91 percent of the volume of the earth’s glacial ice (85 percent of its area) is concentrated in Antarctica, whereas 8 percent of its volume (12 percent of its area) is in Greenland. This means that only 1 percent of the total volume of the earth’s glacial ice exists in the world’s mountain ranges.

Arctic icebergs are the products of glaciers in Greenland, Canada, Alaska, and Russia, but western Greenland is by far the major source of icebergs in the Northern Hemisphere. Icebergs are rare in the north Pacific Ocean because those that are calved from Alaskan glaciers generally drift northward, whereas in the north Atlantic Ocean icebergs generally drift southward (icebergs have been reported as far south as Bermuda).

Another geographical source of icebergs is the Antarctic. Because the immense weight of the Antarctic’s ice sheet has depressed its underlying landmass, most Antarctic ice tends to remain inland rather than flow to the coast. Nevertheless, the sloping coastal edges of the Antarctic ice sheet constantly calve icebergs. For example, in 1927 a section about eight times the size of the state of Rhode Island broke from the Antarctic shore and floated north along the coast of Argentina.

Prevention and Preparations

Because glaciers move slowly and because they are located in sparsely populated regions, they do not pose the same threat to human life and property that icebergs do, but they are not devoid of hazard. Glaciers are capable of overrunning buildings or small settlements, as they did in seventeenth century Switzerland during the start of what came to be called the “Little Ice Age.” Glacial movements can block streams, and when these ice dams fail, human structures and lives are at risk. Today, remote-sensing mapping techniques are able to identify glacial areas of potential dangers to human communities.

Throughout the period of sailing ships and even during the period of steamships, icebergs caused massive loss of life and property. Because of the tragedy precipitated by Titanic’s collision with an iceberg in 1912, an international conference was held in London in 1913 to determine what needed to be done to prevent such disasters in the future. The International Ice Patrol (IIP) began its service in 1914, and through aerial surveillance of icebergs supplemented by observations from commercial ships, the IIP tracked dangerous icebergs, alerted ships to their presence, and prevented collisions. After World War II, radar and sonar techniques were developed to precisely monitor iceberg movements. Canadians were particularly successful in developing airborne ice-mapping sensors, including side-looking airborne radar (SLAR). Scientists from the United States and Canada have also used satellite images to study the loss of glacier mass by calving, and these quantitative data have proved more accurate than estimates based on iceberg reports from ships. A measure of the success of the IIP’s efforts is the fact that, since its inception, not a single reported loss of life or property has occurred from a cooperating vessel’s collision with an iceberg.

Rescue and Relief Efforts

Glacier-related disasters are generally neither as dramatic nor as catastrophic as major earthquakes, but their cumulative costs in property loss and human fatalities mean that survival and rescue become important after such disasters occur. When the lobe of a glacier blocks a stream or an iceberg threatens a seabed oil installation off Labrador, sufficient time exists to evacuate people from a potential glacial surge or to lift workers by helicopter from an oil rig.

During the days of sailing ships, rescues were largely matters of chance. When John Rutledge, traveling from Liverpool to New York, collided with an iceberg off the Newfoundland banks on February 20, 1856, its 120 passengers and 16 crew members tried to survive in five lifeboats (with one compass among them), but by the time Germania picked up one of the lifeboats eight days later, only one young boy remained alive. During the time of the great steamships, the most dramatic rescue of passengers and crew from an iceberg-sunk ship was Titanic. Its 705 survivors owed their lives to the wireless telegraph, for the Cunard liner Carpathia heard Titanic’s SOS messages and sped to the disaster site.

Modern technology has improved survival rates and rescues at sea. Training and drills on ships, emergency alarms, and detailed evacuation systems, as well as superior lifeboats, life rafts, life jackets, and immersion suits, have all facilitated rescues and lessened the loss of life. Because of hypothermia, only 14 people who went down with Titanic were pulled alive out of the water, and only half of those survived. Thermal protective suits now enhance the chances that rescue ships will pull survivors rather than corpses out of cold ocean waters.

Impact

In the early twenty-first century, only a small number of glaciers existed near inhabited areas, minimizing their impact on humans. Icebergs cause disasters on a short time scale, such as collisions with ships, but glacier-related hazards can also be serious when considered on a long-term basis. Variations in the amount of glacial ice are crucial to human populations. Throughout geological history, particularly during the ice ages, glaciers have had a powerful effect on humans and their environment, as they forced our species to adapt or migrate. At the height of the last ice age, about twenty thousand years ago, much more ice existed on continents than exists today, preventing humans from using much valuable land in North America and northern Europe. Some scientists predict that the earth will eventually experience another ice age that might last 50,000 years and that this would have devastating effects on human beings.

On the other hand, many scientists are worried about the effects of future global warming on the earth’s glacial ice. If all this ice were to melt, the resulting rise in sea level of about 200 feet (60 meters) would submerge every major coastal city. Glaciers are sensitive indicators of climate change, expanding and contracting in response to temperature fluctuations. During the lifetime of our species, humans have adapted to immense expansions and contractions of gigantic polar ice sheets, and if the present understanding of glaciologists about the periodic nature of these fluctuations is correct, humans will need to continue their adaptations well into the future.

Bibliography

Benn, Douglas I., and David J. A. Evans. Glaciers and Glaciation. New York: Arnold, 1998. The authors create a contemporary synthesis of “all important aspects of glaciers and their effects.” Particularly valuable is an extensive set of references.

Hoyle, Fred. Ice: The Ultimate Human Catastrophe. New York: Continuum, 1981. In this popular account Hoyle presents the arguments of those scientists who believe that an ice age is imminent, while offering practical suggestions about what needs to be done to avoid its catastrophic consequences.

McCall, G. J. H., D. J. C. Laming, and S. C. Scott. Geohazards: Natural and Man-Made. New York: Chapman and Hall, 1992. This book, written by geoscientists experienced in the practical problems of natural disasters, enlightens readers through descriptions of geohazards (including glaciers and icebergs), their assessment and prediction, and the mitigation of their effects.

Simon, Seymour. Icebergs and Glaciers. New York: HarperTrophy, 1999. Intended for young people. Discusses the formation, movement, and types of glaciers and icebergs. Describes their effect on their surroundings.

Tufnell, L. Glacier Hazards. New York: Longman, 1984. The dangers to human life and property posed by ice sheets in glacierized regions can be significant, and the author shows how to identify such high-risk areas and to reduce their dangers.