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Wednesday, September 23, 2009

by Scoop at Unique Post: Stunning views of glaciers from space

Stunning Views of Glaciers From Space

posted by Scoop, Unique Post, September 2009

To a geologist, glaciers are among the most exciting features on Earth. Though they seem to creep along at impossibly slow speeds, in geologic time glaciers are relatively fast, powerful landscape artists that can carve out valleys and fjords in just a few thousand years.

Glaciers also provide an environmental record by trapping air bubbles in ice that reveal atmospheric conditions in the past. And because they are very sensitive to climate, growing and advancing when its cold and shrinking and retreating when its warm, they can be used as proxies for regional temperatures.

Over geologic time, they have ebbed and flowed with natural climate cycles. Today, the world’s glaciers are in retreat, sped up by relatively rapid warming of the globe. In our own Glacier National Park in Montana, only 26 named glaciers remain out of the 150 known in 1850. They are predicted to be completely gone by 2030 if current warming continues at the same rate.

Here we have collected 13 stunning images of some of the world’s most impressive and beautiful glaciers, captured from space by astronauts and satellites.

Above: Bear Glacier, Alaska

This image taken in 2005 of Bear Glacier highlights the beautiful color of many glacial lakes. The hue is caused by the silt that is finely ground away from the valley walls by the glacier and deposited in the lake. The particles in this “glacial flour” can be very reflective, turning the water into a distinctive greenish blue. The lake, eight miles up from the terminus of the glacier, was held in place by the glacier, but in 2008 it broke through and drained into Resurrection Bay in Kenai Fjords National Park.

The grey stripe down the middle of the glacier is called a medial moraine. It is formed when two glaciers flow into each other and join on their way downhill. When glaciers come together, their lateral moraines, long ridges formed along their edges as the freeze-thaw cycle of the glacier breaks off chunks of rock from the surrounding walls, meet to form a rocky ridge along the center of the joined glaciers.

Heiltskuk Ice Field, British Columbia (above)

Covering nearly 1,400 square miles, the vast Heiltskuk Ice Field lies in the southern Coast Mountains of British Columbia. Taken by an astronaut on the International Space Station, this photo captures the snow-covered mountain slopes as well as several of the ice field’s valley glaciers, which are wide swaths of slowly flowing ice and debris. As these glaciers creep downhill, they carve out large U-shaped valleys that will remain long after the glacier melts. In fact, scientists use these characteristic valleys to identify regions that were once covered in ice but are now glacier-free.

The two largest valley glaciers shown here are the Silverthrone Glacier and the Klinaklini Glacier, which merge with each other at the top of the photo. The dark lines of rock and detritus of the lateral and medial moraines along the edges and middle of the glaciers are clearly visible.

Erebus Ice Tongue, Antarctica (above)

The saw-shaped projection jutting out from this glacier is known as the Erebus Ice Tongue, a long, narrow sheet of ice almost 7 miles long and 33 feet high. This peculiar structure is formed as the Erebus glacier in Antarctica flows rapidly down Mount Erebus and into the McMurdo Sound. During the summer, when the rest of the sea ice in McMurdo melts, the ice tongue floats on the water without thawing. As waves of sea water crash over the sides of the tongue, they carve elaborate shapes and sometimes create deep caves along the edges of the ice sheet. Occasionally, sections of the ice tongue calve off to form small icebergs.

Data for this false-color landscape was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite, and the image was created by combining data in various wavelengths.

Western Greenland Valley (above)

This natural-color image captured in August shows several small glaciers spilling into a mostly dry valley in western Greenland that itself was formed by a glacier in the past. Ground up rock from past glaciations has collected in the valley, giving the pools of water at the snouts of the current glaciers a turquoise color.

The photo was aqcuired by the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite.

Grey Glacier, Chile (above)

Part of the Southern Patagonian Ice Field of Chile and Argentina, Grey Glacier covered 104 square miles when it was measured in 1996. By 2007, when this photograph was taken by astronauts from the International Space Station, the glacier had shrunk considerably, as seen in a comparative false-color image. Scientists think increased regional temperatures and changes in the amount of precipitation have led to more ice calving off as free-floating chunks, and less ice being replenished each year.

In the natural-color image above, Grey Glacier looks pale blue because ice absorbs red wavelengths of light and scatters blue. The rough surface of this part of the glacier is caused by vertical cracks in the surface called crevasses, which are formed near the ends of glaciers as the flow of ice at the bottom speeds up relative to the brittle ice on top.

Eugenie Glacier, Dobbin Bay in the Canadian Arctic (above)

This stunning shot of the Eugenie Glacier in the Canadian Arctic was taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite, which takes high-resolution images designed to detect even minute changes in the extent and features of the world’s glaciers.

This image highlights the fact that glaciers are flowing much like water but at a far slower pace. Smaller glaciers flow down valleys like river tributaries into larger glaciers. The bottom of Eugenie Glacier is floating on the surface of Dobbin Bay; a close-up of the tongue shows extensive surface cracks and calving of small icebergs into the bay.

Retreat of the Helheim Glacier, Greenland (above)

Glaciers stay intact as long as the ice thickness and water depth allow them to stay firmly attached to the ground. But when the ice becomes too thin or the water gets too deep, the tip of a glacier starts to float and rapidly cracks into icebergs, creating what’s called a “calving edge.” This photograph, captured by NASA’s Terra satellite in 2003, shows the calving edge of the Helheim Glacier in Greenland. Comparing similar images from 2001 and 2005 reveals that the solid portion of the glacier has been shrinking rapidly. Measurements from NASA reveal that in just four years, the glacier’s margin retreated 4.7 miles and its flow speed increased from 5 to 7.5 miles per year. Between 2001 and 2003, the thickness of the glacier also shrunk by about 131 feet.

Unfortunately, the entire Greenland Ice Sheet has been undergoing similar shrinkage, thinning by tens of yards in the past decade. While warmer temperatures have certainly caused some of the thinning, scientists also think that the retreat of the ice margin has played a role: With less grounded ice to slow the ice sheet down, it’s moving out to sea at a faster rate.

Ellesmere Island National Park Reserve (above)

This false-color composite image shows a tidewater glacier in the Greely Fjord that extends out over the sea water for a short distance and breaks off into icebergs, which can be seen floating away. The dark spots on the glaciers are likely melt ponds. The pond water is darker than the surface of the glacier and consequently absorbs more heat, which melts more ice and causes the ponds to grow. Sometimes, water from glacial melt ponds will flow through cracks in the glacier to the base, lubricating the surface and causing the glacier to flow more quickly.

Mt. Rainier, Washington (above)

At 14,411 feet, Mt. Rainier is the tallest volcano in the Cascade Range and has a 1,280 foot-wide summit crater. On its eastern slope, it hosts Emmons Glacier, the largest glacier in the lower 48 states. Rainier is an active volcano that is continuously monitored by the U.S. Geological Survey’s Cascade Volcano Observatory. And though it last erupted in 1840, it is considered the most hazardous volcano in the country, in part because of the risk of flooding from melting glaciers in the event of an eruption. This photo was captured on a rare clear day by astronauts on the International Space Station.

Upsala Glacier, Patagonian Argentina (above)

Upsala Glacier is the third largest glacier of the Southern Patagonian Ice Field at around 300 square miles and ends in Lake Argentino. Patagonian glaciers have been retreating rapidly in recent decades, some as much as 2.5 miles between the late 1960s and mid 1990s, making them a target for International Space Station crew observations. Upsala appears to still be retreating with visible changes between this photo taken in 2004 and another from 2000.

Byrd Glacier, Antarctica

The Byrd Glacier near McMurdo Station in Antarctica runs 100 miles through a steep 15-mile-wide valley in the Transatlantic Mountains. This fast-flowing glacier moves ice toward the Ross Ice Shelf at the rate of one half mile a year and adds more ice to the ice sheet than any other glacier. Images such as this one from the U.S. Geological Survey’s Landsat-7 satellite have been combined to form the Landsat Image Mosaic of Antarctica. The mosaic incorporates more than 1,000 images.

Pasterze Glacier, Austria (above)

European glaciers have been rapidly retreating in recent years, due to higher summer temperatures and lower winter precipitation. Pasterze Glacier has been shrinking since 1856. Satellite data such as this image is used by scientists to keep track of the movement of glaciers around the world.

Bering Glacier, Alaska (above)

Bering Glacier, combined with the ice field that feeds it, is the largest glacier in North America at 2,000 square miles, as well as the longest at 118 miles. This glacier has retreated around 7.5 miles and thinned by several hundred yards over the last century, though it is still around 2,500 feet thick in some places. Scientists think the shrinking of Alaskan glaciers such as Bering has reduced the pressure on the boundary between tectonic plates beneath them and consequently increased the number of earthquakes in the region.


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