Glacial surges

Glacial movement occurs at two points in the glacier: at the base and inside. Surging glaciers have left an indelible mark on the landscape in the past and will continue to do so.

Ice-Flow Mechanisms

The surging of glaciers, or spontaneous ice-flooding, began with the inception of the Ice Age. As a field of study, however, it was a long time before glaciologists gave this phenomenon the notoriety that it deserves. Glacial surges have not received much attention because they occur in remote areas and, as a rule, have not been reported. In those cases where the surges have been reported, they are usually completed by the time the scientists arrive. In addition, surges are such infrequent occurrences and of such scattered distribution and short duration that glaciologists have had few opportunities to observe them directly.

As a result, glaciologists do not agree on the specific cause of glacier movements. Glaciers at the foot of precipitous slopes may surge due to avalanches of snow, but that explanation could not account for all surges. The climatic factor cannot be proven to cause glacial surge either, although climate is the primary regulator of a glacier's changing rate of “speed.” While some glaciologists have attempted to show that earthquakes cause glacial surges, most surges occur without the assistance of a big earthquake.

Because the central zone of ice flow is hidden inside the glacier, glaciologists have had to speculate on the mechanism that causes the ice to flow by examining the surface and bottom of the glacier and the degree of deformation in the ice at the snout of the glacier. As a result of these investigations, glaciologists have identified two primary components of movement. The first is basal slip, which involves ice sliding over the floor. The primary mechanism in this process is regelation, which is produced by tiny irregularities on the rock surface. The freezing point is lowered by any increase in the pressure of the ice mass and is raised by any release of pressure; therefore, when the high-pressure side of the irregularity melts the ice, the meltwater flows around the protuberance and refreezes on the downstream, and low-pressure side. This process occurs in a thin zone of ice only 1 or 2 centimeters thick, and the constant displacement in this layer carries the ice along. Although 0.5 millimeters of water is required for this sliding phenomenon, the glacier will move faster if more meltwater is available. Thus, the velocity of a glacier increases during the warm summer months and decreases in the cold winter months. Basal slip is absent in very cold glaciers, where regelation cannot occur.

There is also internal flow inside the glacier, which is much slower and more challenging to study. When snowflakes are buried and pushed together, they become rounded in form. Meltwater that forms at the pressure points between crystals refreezes and is added only to certain crystals. As a result, some crystals grow at the expense of others. A glacier is formed as the deepening of the snow and the continued refreezing of meltwater force out the air. It converts the individual crystals into a single mass of interlocking crystals. When subjected to steadily applied pressure, which may result from the weight of the ice or the pull of gravity, the tiny atomic layers that compose each crystal begin to slide over each other. Recrystallization occurs as the pressure causes the crystals to orient themselves so that their atoms are parallel to the glacier's surface. After billions of crystals rearrange themselves in this favorable direction, the glacier begins to move.

Rates and Types of Movement

During a glacial surge, different parts of the glacier move at different rates. There are two basic zones of ice movement. The zone of fracture, which is an upper zone between 30 and 60 meters thick, consists of brittle ice that breaks sharply. In contrast, pressure exerted by the upper layer of ice causes the lower layers to behave like plastic in the zone of flow. The plastic deformation of the ice mass allows the ice to flow in the lower zone, which carries the overlying rigid ice along with it.

A less important mode of flow is a shearing type of motion that some glaciers exhibit. This phenomenon occurs because the zone of flow does not proceed at a uniform rate. The more plastic ice can adjust to this differential flow, but the brittle ice cannot and starts to crack and splinter. This breakdown usually happens near the glacier's snout.

Although surge rates of up to 20 meters per day have been recorded, most glaciers move only about 1 meter per day. Some overly energetic glaciers have been known to “gallop” or advance at phenomenal speed rates. Whenever there are clusters of glaciers, one or more occasionally starts racing ahead of the others. Canada's Steele Glacier, for example, is a galloping glacier that flows at about 0.6 meters per hour. The Alps, Iceland, and Scandinavia have supplied hundreds of reports over the years of glaciers that snaked into valleys, knocked down orchards, blanketed fields and pastures, and demolished roads and buildings.

Study of Glacial Surges

During the nineteenth century, naturalist Louis Agassiz proved that ice motion is fastest in the center and decreases toward the sides by driving stakes across glaciers. More recently, glaciologists have drilled vertical holes in glaciers and inserted pipes into the holes. After taking careful measurements, they found that the glacier bent the pipes as time passed. By measuring the bending of the pipes, they found that the deeper the ice below the surface, the slower it flows. Glaciologists also study the movement of glaciers by examining the deposits left behind. These deposits, called drift, are either heterogeneous collections of stony material or uniformly graded material. Drift layers can be distinguished by their composition, color, and degree of weathering. Glaciologists assume that the earliest ones followed a growth pattern similar to the last ones, of which scientists have the clearest picture. Because drift layers overlap one another and have similar shapes, scientists believe that recurring ice sheets grew out of the same source regions and moved in approximately the same directions.

Glaciologists employ several methods to study the direction of ice movement. A composite picture of movement can be formed by studying the striations cut into the bedrock by large, sharp rocks embedded in the base of the moving ice. These striations, some of which are a few meters deep and up to hundreds of meters long, are more pronounced on hillsides and outcrops that face the glacier. One of the best indicators of the direction of travel is erratic boulders, the largest objects deposited by glaciers. Because glaciers cannot move backward, their location leaves no doubt about which way the ice went. The distinctive characteristics of a rock can tell a geologist where it came from. For example, if a rock can be identified as coming from an area in the northeast, the geologist knows that the ice moved in a southwesterly direction. Airplanes are also used to ascertain the ice's direction of travel. Viewed from the air, the paths of the glacier can be clearly seen. In central Canada, for example, elongated hills and valleys and long, narrow lakes have been smoothed in lines parallel to the glacier's path.

Landforms built by the ice illustrate how the ice made its retreat. The manner and direction of the ice's withdrawal are revealed by the composition and arrangement of the drift. They show the ice sheet shape and where the glacier halted during its retreat. In addition to studying the movement of ice, glaciologists have applied scientific methods to determine the date of these glacier advances. In 1879, Swedish geologist Baron Gerard de Geer began his study of varves, the sediment layers in the exposed beds of glacial lakes. Because the lowest varve is laid down when the glacier retreats, Geer was able to count the years since it disappeared. However, this method is not entirely accurate because some varves have been scattered over a wide range.

Radiocarbon dating, developed in 1947 by American physical chemist Willard F. Libby, is a much more reliable method of dating glaciers. This method takes advantage of the fact that the radioactive isotope of carbon, known as carbon-14, changes at a constant rate. By measuring the amount of radioactivity in the remains of a dead plant or animal deposited by a glacier, geologists have been able to extend the glacial calendar backward for nearly 70,000 years. The pollen grains embedded in peat bogs, many of which are the remnants of shallow glacial lakes, have enabled scientists using carbon-14 dating to determine the times when various forests covered the landscapes.

Using a related method of dating, chemist and Nobel laureate Harold C. Urey discovered a method of finding the temperature at which a shelled creature lived by analyzing another isotope: oxygen-18. The greater the proportion of oxygen-18, the higher the water temperature. Oxygen isotopes tell scientists the sediment temperature when they were deposited, which reflects what was happening in the frozen world on land.

Environmental Impacts

In many ways, glaciers are almost as important as air, soil, and water in their effect on humankind's future. According to the US Geological Survey, in 2024, 68.7 percent of all the earth's freshwater was stored in glacial ice, while 30 percent was found in groundwater. In North America, the volume of freshwater stored in glaciers is far greater than that held in all the continent's rivers, ponds, and lakes combined. Melting mountain glaciers produce fresh water for irrigation in many parts of the world. Glaciers provide much of the water for the world's great river systems. Thus, the availability of this water to humans depends on the condition of the glacier. As glaciers advance, more water is locked up in the ice. However, when glaciers shrink and retreat, the water is released from storage. As one can see, the retreat or advance of a glacier tremendously affects the water resources that depend on it.

Glacier movement also has important implications for mining because it aids geologists and prospectors in tracking down the source of valuable erratics such as diamonds. Because diamonds can withstand tremendous grinding and travel great distances without disintegrating, the volcanic source from which they came may be many miles from where they were found. Nevertheless, many geologists and prospectors have hunted for the source of diamonds, such as those found in the drift of Wisconsin, Indiana, Ohio, and Michigan.

Many scientists believe that vast ice sheets will again spread over North America and Europe. Taking thousands of years, this process will transform large-scale agriculture into small-scale subsistence farms. As the ice advances, Chicago, for example, without moving an inch, will become a city of the subarctic within ten thousand years. Even if glaciers did not affect the Earth, they would be of value simply because of their beauty and majesty. Massive glaciers that dominate the land in many parts of the world have attracted nature lovers and explorers for years. This beauty could be lost forever if mining operations are conducted underneath the glaciers, as some people have suggested.

Although scientists cannot precisely predict where and when the great ice masses will move, they believe humankind is hastening their movement. The gradual warming of the Earth is being accelerated by the increasing amounts of carbon dioxide created due to the burning of mineral fuels, such as coal, oil, and gas. This warming trend could not only result in excessive melting of the ice sheets and produce a dangerous rise in sea level but also enable air masses to carry more snow on the glaciers’ feeding grounds and cause them to grow.

As anthropogenic climate change continues in the twenty-first century, understanding the mechanics behind glacial surges has become increasingly important. Researchers at Dartmouth University and the Massachusetts Institute of Technology have developed a physics-based model that adapts earthquake and landslide mechanics to glaciers. This method studies the surface beneath the glacier's bottom and the hydraulic system within and beneath the glacier. The use of this system may make glacial surge predictions more straightforward and accurate, mitigating the effects of catastrophic sea level rise. 

Principal Terms

basal slip: glacier movement that is caused when the glacier slides over its floor

drift: an all-inclusive term for any kind of material that is deposited by glaciers and their meltwater

erratic: a glacier-transported rock fragment resting on bedrock unlike that from which the fragment was derived

glaciation: the effects of a glacier upon the landscape

glaciologists: scientists who specialize in the study of glaciers and ice

internal flow: movement that occurs as the individual ice crystals are slowly deformed; this motion enables the glacier to flow over irregular surfaces and around curves

meltwater: water from the melting of ice and snow

regelation: the freezing and thawing of ice as the result of changes in pressure

snout: the terminal end of a glacier

striation: parallel scratches cut in bedrock over which the glacier has passed

till: unsorted, unconsolidated glacier-deposited material that was let down directly from the ice and does not include material deposited by meltwater

varve: a pair of contrasting layers of sediment deposited over one year; the summer layer is light, and the winter layer is dark

Bibliography

Bendle, Jacob. "Surging Glacier Landsystem." Antarctic Glaciers, 2020, www.antarcticglaciers.org/glacial-geology/glacial-landsystems/surging-glacier-landsystem. Accessed 15 Apr. 2023.

Bennett, Matthew M., and Neil F. Glassner, editors. Glacial Geology: Ice Sheets and Landforms. 2d ed., Hoboken, Wiley-Blackwell, 2013.

Binder, Andrew. “Glacier Surges: Scientists Lift the Hood on a Natural Disaster.” National Association of Science Writers, 2020, www.nasw.org/article/glacier-surges-scientists-lift-hood-natural-disaster. Accessed 21 July 2024.

Bloom, Arthur G. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. 3rd ed., Waveland Press, 2004.

Copland, Luke, et al. “The Distribution and Flow Characteristics of Surge-Type Glaciers in the Canadian High Arctic.” Annals of Glaciology, vol. 36, 2003, pp. 73–81., doi.org/10.3189/172756403781816301. Accessed 15 Apr. 2023.

Dolgoff, Anatole. Physical Geology. Houghton Mifflin Harcourt, 1999.

“Earth's Fresh Water.” National Geographic Society, 26 Jan. 2024, education.nationalgeographic.org/resource/earths-fresh-water. Accessed 21 July 2024.

“Glacier Quick Facts.” National Snow and Ice Data Center, nsidc.org/learn/parts-cryosphere/glaciers/glacier-quick-facts. Accessed 21 July 2024.

Hambrey, Michael, and Jurg Alean. Glaciers. 2d ed., Cambridge UP, 2004.

Imbrie, John, and Katherine Imbrie. Ice Ages: Solving the Mystery. Reprint. Enslow, 2000.

Jiskoot, H., and D. T. Juhlin. “Surge of a Small East Greenland Glacier, 2001–2007, Suggests Svalbard-Type Surge Mechanism.” Journal of Glaciology, vol. 55, no. 191, 2009, pp. 567–570, doi.org/0.3189/002214309788816605. Accessed 15 Apr. 2023.

Kurtén, Bjorn. Dance of the Tiger: A Novel of the Ice Age. U of California P, 1995.

Mathews, William H. The Story of Glaciers and the Ice Age. Irvington, Harvey House, 1974.

Menzies, M., editor. Modern Glacial Environments: Processes, Dynamics, and Sediments. Butterworth-Heinemann, 1996.

Moore, John, and Louise Lerner. “Scientists Call for 'Major Initiative' to Study whether Geoengineering Should be Used on Glaciers.” ScienceDaily, 11 July 2024, www.sciencedaily.com/releases/2024/07/240711111528.htm. Accessed 21 July 2024.

Schultz, Gwen. Ice Age Lost. Garden City, Doubleday, 1974.

Sparks, John. Planet Earth. Garden City, Doubleday, 1977.