The upper layers of glaciers are more brittle, and often form deep cracks known as crevasses or bergschrunds as they move.
Glacial erratics are rounded boulders that were left by a melting glacier and are often seen perched precariously on exposed rock faces after glacial retreat.
Arкtes can also be produced by the collision of two parallel glaciers.
The smallest alpine glaciers form in mountain valleys and are referred to as valley glaciers.
Glaciers are also responsible for the creation of fjords (deep coves or inlets) and escarpments that are found at high latitudes.
Rocks and sediments are added to glaciers through various processes.
Glacial moraines are formed by the deposition of material from a glacier and are exposed after the glacier has retreated.
Both of these features are left on the surfaces of stationary rock that were once under a glacier and were formed when loose rocks and boulders in the ice were transported over the rock surface.
The Hubbard Glacier is the longest tidewater glacier in Alaska and has a calving face over ten kilometers long.
On the opposite end of the glacier, at its foot or terminal, is the deposition or ablation zone, where more ice is lost through melting than gained from snowfall and sediment is deposited.
Transport of fine-grained material within a glacier can smooth or polish the surface of rocks, leading to glacial polish.
Sub-polar glaciers have a seasonal zone of melting near the surface and have some internal drainage, but little to no basal melt.
Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
The word glacier comes from French via the Vulgar Latin glacia, and ultimately from Latin glacies meaning ice.
The geothermal heat flux becomes more important the thicker a glacier becomes.
After the glacier melts, these corries are usually occupied by small mountain lakes called tarns.
Terminal or end moraines are formed at the foot or terminal end of a glacier.
which makes the ice at the bottom of the glacier move slower than the upper portion.
Due to erosive forces at the edges of the moving ice, glaciers turn V-shaped river-carved valleys into U-shaped glacial valleys.
A glacier is a large, slow-moving river of ice formed from compacted and crystallized layers of snow.
Ice caps feed outlet glaciers, tongues of ice that extend into valleys below, far from the margins of those larger ice masses.
Yakutat Bay and Glacier Bay are both popular with cruise ship passengers because of the huge glaciers descending hundreds of feet to the water.
When directly measured this is glacier mass balance.
Crevasses form due to internal differences in glacier velocity between two quasi-rigid parts above the deeper more plastic substrate far below.
The ice of polar glaciers is always below the freezing point, so most of their mass loss is due to sublimation.
A glacier slowly deforms and flows in response to gravity.
Lateral moraines are formed on the sides of the glacier.
Most tidewater glaciers calve above sea level, which often results in a tremendous splash as the iceberg strikes the water.
An elongated, rounded, asymmetrical, bedrock knob can be produced by glacier erosion.
Tidewater glaciers are alpine glaciers that flow into the sea.
In both mechanisms the radiation imbalance of the earth is thought to play a large role in the build-up and melt of glaciers.
Stoss-and-lee erosional features are formed by glaciers and show the direction of their movement.
The snow that forms temperate glaciers is subject to repeated freezing and thawing, which changes it into a form of granular ice called nйvй.
When the glacier moves through irregular terrain, cracks form in the fracture zone.
Plateau glaciers resemble ice sheets, but on a smaller scale.
Other features formed by glacial deposition include long snake-like ridges formed by streambeds under glaciers, known as eskers, and distinctive streamlined hills, known as drumlins.
The Pleistocene had periods when the glaciers retreated (interglacial) because of mild temperatures, and advanced because of colder temperatures (glacial).
A glacier may also erode its environment through katabatic winds.
Glacial meltwaters contain rock flour, an extremely fine powder ground from the underlying rock by the glacier's movement.
The higher altitude part of a glacier that receives most of the snowfall is called the accumulation zone.
The top 50 meters of the glacier are more rigid.
At the 'start' of a classic valley glacier is the cirque, which has a bowl shape with escarped walls on three sides, but open on the side that descends into the valley.
The glacier abrades the smooth slope that it flows along, while rock is torn loose from the downstream side and carried away in ice, a process known as "plucking."
In alpine glaciers, friction generated at the valley's side walls also slows the edges relative to the center.
Glaciers erode the terrain principally through two methods: abrasion and plucking.
The largest glaciers are continental ice sheets, enormous masses of ice that not visibly affected by the landscape and covering the entire surface beneath them, except possibly on the margins where they are thinnest.
Glacier retreat has accelerated since about 1980 and is correlated with global warming.
A large mass, such as an ice sheet/glacier, depresses the crust of the Earth and displaces the mantle below.
The extent of the glacier ice during the Pleistocene, however, was not static.
The place where the glacier thins to nothing is called the ice front.
Glaciers cover vast areas of the polar regions but in the tropics are restricted to the highest mountains.
Materials that become incorporated in a glacier are typically carried as far as the zone of ablation before being deposited.
Africa has glaciers on Mount Kilimanjaro, Mount Kenya and in the Ruwenzori Range.
Glaciers occur on every continent and in approximately 47 of the world's countries.
Larger glaciers can cover an entire mountain, mountain chain or even a volcano; this type is known as an ice cap.
Long linear rock scratches (that follow the glacier's direction of movement) are called glacial striations, and divots in the rock are called chatter marks.
The "heartland," Central Thailand, is a natural self-contained basin often termed "the rice bowl of Asia."
After the glacier melts the mantle begins to flow back to its original position pushing the crust back to its original position.
Below its top 10-20 meters (33-66 feet), a temperate glacier is at the pressure melting point of ice throughout the year, which permits the glacier to deform in response to gravitational force.
Craftsmen in Lahore produce almost every type of hand-made carpet using popular motifs such as medallions, paisleys, traceries, and geometric designs.
Some rock formations in the path of a glacier are sculpted into small hills with a shape known as roche moutonnйe or sheepback.
The water that rises from the ablation zone moves away from the glacier and carries with it fine eroded sediments.
The lower layers of glacial ice flow and deform plastically under the pressure, allowing the glacier as a whole to move slowly like a viscous fluid.
Isostatic rebound is a rise of a part of the crust due to an isostatic adjustment after a glacier recedes.
Outlet glaciers are formed by the movement of ice from a polar ice cap, or an ice cap from mountainous regions, to the sea.
When a glacier reduces in size to a critical point, its flow stops, and the ice becomes stationary.
During these surges, the glacier may reach velocities up to 100 times greater than normal.
Less apparent is the ground moraine, also called glacial drift, which often blankets the surface underneath much of the glacier downslope from the equilibrium line.
Glacial meltwaters flow throughout and underneath glaciers, carving channels in the ice (called moulins) similar to cave formation through rock and also helping to lubricate the glacier's movement.
Many glaciers deepen their valleys more than their smaller tributaries.
Medial moraines are formed when two different glaciers, flowing in the same direction, coalesce and the lateral moraines of each combine to form a moraine in the middle of the merged glacier.
Many glaciers have periods of very rapid advancement called surges.
After the glacier is gone, this often leaves a bowl or amphitheater-shaped isostatic depression called a cirque.
Most of the concepts in this article apply equally to alpine glaciers and continental glaciers.