Erosional Landforms

A number of landforms result from the movement of glaciers across Earth's surface. Such features in present-day glaciers range from rock polish and glacial grooves on smaller scales to hanging valleys and drumlins on larger ones. Most recently during the Pleistocene Epoch (about 2.6 million to 11,700 years ago), vast continental ice sheets reached into the middle latitudes. Most scientists maintain that these ice sheets carved out many of the world's present-day freshwater basins. Small-Scale...

Rtver Tce Modification

There are a variety of means of modifying ice in rivers. Icebreaking vessels are used to clear paths for other vessels and occasionally to assist in relieving jams on large rivers. Icebreakers are used extensively in northern Europe and to some extent on the Great Lakes and St. Lawrence River of North America. Dusting the ice cover with a dark material such as coal dust or sand can increase the absorption of solar radiation and thus create areas of weakness that aid in an orderly breakup....

The OrigiN of Arctic Icebergs

Iceberg Type

Most Arctic icebergs originate from the fast-flowing glaciers that descend from the Greenland Ice Sheet. Many glaciers are funneled through gaps in the chain of coastal mountains. The irregularity of the bedrock and valley wall topography both slows and accelerates the progress of glaciers. These stresses cause crevasses to form, which are then incorporated into the structure of the icebergs. Arctic bergs tend to be smaller and more randomly shaped than Antarctic bergs and also contain inherent...

The Arctic Ocean

Smallest of the world's oceans, centring approximately on the North Pole, the Arctic Ocean and its marginal seas (the Chukchi, East Siberian, Laptev, Kara, Barents, White, Greenland, and Beaufort some oceanographers also include the Bering and Norwegian seas) are the least-known basins and bodies of water in the world ocean. This lack of knowledge about them results from their remoteness, hostile weather, and perennial or seasonal ice cover. This is changing, however, because the Arctic may...

General Considerations

In order to gain a solid understanding of the different landforms produced by glaciers and their meltwater, it is helpful to discuss the glacial environment and the processes responsible for the formation of such structures. There are numerous types of glaciers, but it is sufficient here to focus on Eskers, narrow ridges of gravel and sand left by a retreating glacier, wind through western Nunavut, Canada, near the Thelon River. Richard Alexander Cooke III two broad classes mountain, or valley,...

Ice Formation In Rivers

The formation of ice in rivers is more complex than in lakes, largely because of the effects of water velocity and turbulence. As in lakes, the surface temperature drops in response to cooling by the air above. Unlike lakes, however, the turbulent mixing in rivers causes the entire water depth to cool uniformly even after its temperature has fallen below the temperature of maximum density (4 C, or 39 F). The general pattern is one in which the water temperature fairly closely follows the...

Depostttonal Landforms

The movement of glaciers across terrestrial environments disturbs the underlying layers of soil and rock, eventually delivering and depositing the collected material to the end, or margin, of the glacier. As a glacier moves along a valley, it picks up rock debris from the valley walls and floor, transporting it in, on, or under the ice. This scouring process also occurs in continental glaciers. When the material reaches the lower parts of the glacier where ablation is dominant, it is...

Decay And Ice Jams

In late winter, as air temperatures rise above the freezing point, river ice begins to melt owing to heat transfer from above and to the action of the slightly warm water flowing beneath. As occurs in lake ice, river ice also may deteriorate and rot because of absorption of solar radiation. On the undersurface, the action of the turbulent flowing water causes a melt pattern in the form of a wavy relief, with the waves oriented crosswise to the current direction. Eventually, if the ice cover is...

Iceberg Scour and SeDiMeNT Transport

When an iceberg runs aground, it can plow a furrow several metres deep in the seabed that may extend for tens of kilometres. Iceberg scour marks have been known from the Labrador Sea and Grand Banks since the early i970s. In the Arctic, many marks are found at depths of more than 400 metres (1,300 feet), whereas the deepest known sill, or submerged ridge, within Greenland fjords is 220 metres (about 725 feet) deep. This unsolved anomaly suggests that icebergs were much deeper in the past or...

Ice Formation Tn Lakes

The setting for the development of ice cover in lakes is the annual evolution of the temperature structure of lake water. In most lakes during the summer, a layer of warm water of lower density lies above colder water below. In late summer, as air temperatures fall, this top layer begins to cool. After it has cooled and has reached the same density as the water below, the water column becomes isothermal (i.e., there is a uniform temperature at all depths). With further cooling, the top water...

Active Wedges Inactive Wedges And Icewedge Casts

Ice wedges may be classified as active, inactive, and ice-wedge casts. Active ice wedges are those that are actively growing. The wedge may not crack every year, but during many or most years cracking does occur, and an increment of ice is added. Ice wedges require a much more rigorous climate to grow than does permafrost. The permafrost table must be chilled to -15 to -20 C (5 to -4 F) for contraction cracks to form. On the average, it is assumed that ice wedges generally grow in a climate...