At this point, the glacier begins to move under its own weight. Ice sheets tend to be slightly dome -shaped and spread out from their center. They behave plastically , or like a liquid.
An ice sheet flows, oozes, and slides over uneven surfaces until it covers everything in its path, including entire valleys, mountains, and plains.
Compression and geothermal energy sometimes cause the bottom of an ice sheet to be slightly warmer than the ice above it. The bottom of the ice sheet melts, causing the ice above it to move at a faster rate than the rest of the ice sheet. These fast-moving glaciers are called ice stream s. Ice streams can move as quickly as 1, meters. The slightly warmer, softer ice of the ice stream is where most of the ice sheet's crevasse s are located. The largest glacier in the world is an ice stream, the Lambert Glacier in Antarctica.
The Lambert Glacier moves as quickly as 1, meters. It is more than kilometers miles long and 2, meters 1. Continental Glaciers The Antarctic ice sheet is the largest block of ice on Earth.
It covers more than 14 million square kilometers 5. The Antarctic ice sheet is about 2 kilometers 1. If it melted, sea level would rise by about 60 meters feet. The Greenland ice sheet is much smaller than the Antarctic Ice sheet, only about 1. It is still the second-largest body of ice on the planet.
The Greenland ice sheet interacts much more dynamically with the ocean than the Antarctic ice sheet. The annual snow accumulation rate is more than double that of Antarctica. Glacial melt happens across about half of the Greenland ice sheet, whereas it is much more isolated on the far western part of Antarctica.
Greenland's ice shelves break up much faster than those surrounding Antarctica. Both the Antarctic and Greenland ice sheets have caused the land under them to sink. Eastern Antarctica is about 2. If the continental glaciers were to suddenly disappear, the landscape of Antarctica and Greenland would change drastically. Antarctica would shrink by more than a quarter as the western part shrunk into the sea. Greenland, the largest island in the world, would become an archipelago , a chain of small islands only connected by waterways.
Ice Sheets in History Antarctica has been covered by an ice sheet for 40 million years. While the ice sheet has advanced and retreated with climate change, it has been a constant feature of the landscape the entire time. This was the last glacial period, or ice age.
Ice sheets reached their greatest size about 18, years ago. It once spread as far west as the island of Great Britain and as far east as Moscow, Russia. It originated in the Jostedalsbreen area of southern Norway, where it eventually retreated. Jostedalsbreen remains the largest glacier in Europe today. As it retreated to the Barents Sea, it created shallow lakes that still dot northern Russia. Although most of what is today Chile was covered in ice, the Patagonian Ice Sheet did not spread as far west as the Argentine coast, or connect with the ice caps of the Altiplano.
The dry climate of central Argentina and the arid Atacama Desert restricted the reach of the ice sheet. In the central thickest parts, the ice flows almost vertically down toward the base, while at the edges of the glacier, it flows horizontally out toward the margins. In continental glaciers like the Antarctic and Greenland Ice Sheets, the thickest parts 4, m and 3, m thick, respectively are the areas where the rate of snowfall, and therefore of ice accumulation, are greatest.
In Antarctica, the ice sheet flows out over the ocean, forming ice shelves. Ice shelves can slow the flow of continental glaciers outward. Conversely, if ice shelves break down continental glacier flow can speed up.
Alpine glaciers aka valley glaciers originate high up in the mountains, mostly in temperate and polar regions Figure The flow of alpine glaciers is driven by gravity, and primarily controlled by the slope of the ice surface Figure Alpine glaciers grow due to accumulation of snow over time.
In the zone of accumulation , the rate of snowfall is greater than the rate of melting. In other words, not all of the snow that falls each winter melts during the following summer, and the ice surface in the zone of accumulation does not lose its annual accumulation of snow cover over the course of the year. In the zone of ablation , the rate of melting exceeds accumulation. The equilibrium line marks the boundary between the zones of accumulation above and ablation below Figure Above the equilibrium line of a glacier, winter snow will remain even after summer melting, so snow gradually accumulates on the glacier over time.
The snow layer from each year is covered and compacted by subsequent snow, and it is gradually compressed and converted to firn Figure Firn is a form of ice that forms when snowflakes lose their delicate shapes and become granules due to compression. With more compression, the granules are squeezed together, and air is forced out. Downward percolation and freezing of water from melting contributes to the process of ice formation.
The equilibrium line of a glacier near Whistler, BC, is shown in Figure Below this line is the zone of ablation. Above this line the ice is still mostly covered with snow from the previous winter.
The position of the equilibrium line changes from year to year as a function of the balance between snow accumulation in the winter, and snow and ice melt during the summer. If there is more winter snow and less summer melting, this favours the advance of the equilibrium line down the glacier and ultimately increases the size of the glacier. Cool summers promote an increase in glacier size, and thus lead to advance of the equilibrium line. Greenland and Antarctica The largest glaciers are continental ice sheets or icecaps, enormous masses greater than 50, square kilometers [12 million acres] of ice found only in Antarctica and Greenland.
Climate Change Facts Why do glaciers matter? What is a glacier? How does a glacier form? Types of Glaciers and how they behave What story does ice tell? According to Truffer, that spread depends on water temperature, too, which Willis points out will be revealed when the GRACE mission reveals its mass findings in the coming months. Air temperature probably is important, and so is snowfall, adds Willis. But we know that what we saw was caused by the ocean because the slowing and thickening is concentrated right where the ice meets the water.
The thickening gets smaller and smaller as you move inland. The interaction of warm currents eroding ocean-facing glaciers already impacts Antarctica ; 10 percent of its coastal glaciers are currently in retreat.
Between and , oceans warmed an average of 60 percent more per year than the Intergovernmental Panel on Climate Change has estimated. From mineral mining to shipping lanes, fishing and strategic claims ranging from China to Russia , the change in the ice has a myriad of ripples. A reduction of ice loss in glaciers like Jakobshavn could mean less dangerous icebergs traveling south into the Atlantic, a menace to shipping routes—or it could mean that all the underwater calving could create more ice floes.
Twenty billion tons of ice dump into the sea from Jakobshavn annually, more than anywhere besides Antarctica, with bergs scooped by the Labrador Current. Read about a massive new iceberg in Antarctica. All rights reserved. Maybe not quite the way we think. Complex interactions Glaciers like Jakobshavn extend out into the ocean, which explains how water temperature can impact their size and movement and may mean that the overall melting trend—while still happening—may be happening slower than we thought.
Share Tweet Email. Why it's so hard to treat pain in infants. This wild African cat has adapted to life in a big city. Animals Wild Cities This wild African cat has adapted to life in a big city Caracals have learned to hunt around the urban edges of Cape Town, though the predator faces many threats, such as getting hit by cars.
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