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Earth from Space – ice island poses a hazard

Satellite image of ice island PII-A

A 251-square-kilometre ice island, calved from the Petermann Glacier, is drifting off the Labrador coast in Canada.

NEARLY 11 MONTHS AFTER BREAKING OFF the northwestern coast of Greenland, a massive ice island is now caught up in ocean currents off the coast of Labrador, Canada.

The ice island was formed when a 251-square-kilometre chunk of ice calved off the Petermann Glacier on August 5, 2010. The Canadian Ice Service has since been tracking the ice island, dubbed PII-A, via satellite and radio beacon.

NASA’s Aqua satellite captured this natural-colour image of the ice island on June 25, 2011. The northeast-facing coast of Labrador is mostly obscured by thin, wispy clouds.

News agencies reported that the ice island stretched roughly 62 square kilometres in area and weighed between 3.5 and 4 billion tons.

The island has been slowly breaking up and melting on its journey—over nearly 30 degrees of latitude, or more than 3,000 kilometres—but it could eventually pose a hazard to offshore oil platforms and shipping lanes off Newfoundland.

Canadian fishermen captured a close-up video of the ice island.

Environment Canada dropped a radio beacon on PII-A on September 17, 2010. You can track the island by clicking here.

NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC. Text adapted from information issued by Michael Carlowicz.

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Greenland’s changing landscape

Petermann Glacier and iceberg

A massive iceberg broke from the Petermann Glacier in Greenland on August 5.

On August 5, 2010, the unassuming Petermann Glacier on Greenland’s northwestern coast hit the world’s headlines when a huge ice island “calved” from it and started drifting down a fjord.

Eleven days later, the island was continuing its slow migration down the fjord. The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured a natural-colour image (above) on August 16, 2010.

Although slivers of ice had loosened around its edges, the ice island had largely retained its original shape. The island, which had rotated counterclockwise since the calving, also retained the crevassed structure of the Petermann Glacier; both the glacier and the ice island sport rippled surfaces.

Thin longitudinal cracks appear on the ice island surface, and wider lateral cracks push in from the island’s sides. An uneven line of pools, medium blue in colour, runs down the length of the ice island.

Along the glacier’s new front, some smaller icebergs appear to have broken free, and ice fragments litter the water surface between the ice island and the glacier. Also visible in the image are multiple small glaciers that feed the Petermann, flowing down to the massive glacier from the northeastern side of the fjord.

See the full-size, high-resolution image here (4MB, new window).

Phytoplankton bloom off the east coast of Greenland.

Satellite image of a phytoplankton bloom off the east coast of Greenland.

Meanwhile, on Greenland’s eastern seaboard, the stark black and white landscape of provides a fine palette for the burst of colour created by a large phytoplankton bloom, spotted by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra  satellite on August 7, 2010.

The bloom blends shades of milky blue, turquoise, and green, created by different species of phytoplankton growing in the cold, nutrient-rich waters. Likely shaped by the East Greenland Current, the bloom extends along the southeast coast of Greenland.

The full length of the bloom is visible in the large image (0.7MB, new window), which shows a broader area.

The phytoplankton bloom is not the only source of colour in the scene. The brilliant white of the ice sheet fades to grey in places along the shore where old ice is exposed. Tinted faintly brown like the craggy brown rocks that channel them, glaciers seep from the ice sheet into fjords, rivers of ice draining the great ice sheet. The glaciers give way to green-blue water, milky with the fine sediment created as the ice grinds over rock.

These waters and the deep black-blue waters of the Atlantic Ocean are dotted with icebergs. No more than tiny white specks at this scale, the icebergs resemble tiny grains of salt floating on the water’s surface.

NASA images courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC; and Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team and the United States Geological Survey. Text adapted from information issued by Michon Scott and Holli Riebeek.

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Antarctic glacier retreats

Image of Crane Glacier on the Larsen B Ice Shelf on April 6, 2002

This image of Crane Glacier on the Larsen B Ice Shelf on the Antarctic Peninsula was captured on April 6, 2002. Compare with the image below.

In late Southern Hemisphere summer of 2002, the Larsen B Ice Shelf on the Antarctic Peninsula disintegrated into thousands of pieces.

The collapse appears to have been due to a series of warm summers on the Antarctic Peninsula, which culminated with an exceptionally warm summer in 2002. On the surface of the shelf, rows of melt ponds settled into natural crevasses, driving the cracks all the way through the ice shelf.

This pair of images from NASA’s Landsat 7 satellite shows the dramatic impact the collapse had on many of the glaciers that fed the Larsen B Ice Shelf. The loss of the shelf caused the flow of most of the glaciers around the bay to accelerate significantly. More rapid flow and calving of icebergs caused the margins to retreat inland.

The image above was captured on April 6, 2002, about two months after the dramatic collapse. The bay (image right) is filled with slush and icebergs from the collapsed shelf.

Autumn snows have probably already dusted the surface of the mélange of ice; snowfall and seasonal sea ice kept much of the debris frozen in place the first winter after the collapse. The terminus of the Crane Glacier extends into the bay like a fan.

Throughout the summer of 2003, remaining fragments of the shelf broke away, and the mélange of icebergs and smaller ice pieces from the previous summer’s collapse began to drift away.

Without the stabilizing presence of the ice shelf, the Crane Glacier retreated dramatically. Its fan-shaped terminus became C-shaped as the glacier’s centre crumbled more rapidly than the edges pressed against the mountain walls.

By 2003, Crane Glacier had retreated dramatically

By 2003, Crane Glacier had retreated dramatically as fragments of the ice shelf broke away.

The unusually bright blue tinge of the ice debris in the February 20 image (above) is the reflection from the pure ice on the underside of the ice shelf fragments. Many of the icebergs that crumbled from the edge of the shelf were too tall and narrow to float upright, and they toppled over.

The surface of an ice shelf gets covered by snow, but the underside is very pure ice. Pure, thick ice absorbs a small amount of red light. Photo-like satellite images such as these are made by combining the satellite’s observations of red, green, and blue wavelengths of light reflected from the Earth’s surface. When all these visible wavelengths are strongly reflected, the surface looks white; when the reddest light is absorbed, the reflection takes on a bluish tinge.

NASA images by Robert Simmon based on Landsat-7 data. Text adapted from information issued by Rebecca Lindsey.