What you need to know about glacial melt – Daily Bulletin
The recent study of the Intergovernmental Panel on Climate Change report released what it calls a code red for humanity due to increasingly extreme heat waves and record temperatures.
More than 80% of Greenland – an area about three times the size of Texas – is covered by an ice cap up to 3 km thick. Satellite imagery confirms that the ice sheet is thinning due to the acceleration of glaciers and the discharge of more ice than it accumulates due to snowfall, a process known as dynamic thinning.
THE ACCELERATING FLOW OF PETERMANN: The Petermann Glacier in northwest Greenland is an outlet glacier – a tongue of ice that extends from an ice cap. Outlet glaciers flow into an open area or ocean and typically occupy a depression or irregular fjord. The Petermann drains 7% of the Greenland ice sheet and its flow increases.
The upper pelvis is a part of the ice cap 60 miles wide and up to 1.8 miles thick. Its base rests on a bedrock, much of which has been sunk below sea level by its immense weight. It is slowly sinking towards the edge of the ice cap.
The fjord is a water-filled depression in the bedrock into which the glacier flows. It is 18 miles wide at ice cap level and 9 miles as it approaches the sea. Known as the land line, the point at which the glacier’s ice begins to float is about 50 miles upstream of the fjord from its snout.
1. Internal glass: As the glacier flows faster downstream and thinner, the ice discharge inland increases dramatically, accelerating the rate of depletion of the Greenland ice sheet.
2. Side drag: Friction on the fjord walls helps stabilize the floating ice and is transmitted upstream, where it affects the flow of interior ice into the glacier. Reduced drag on the flanks results in accelerated flow of interior ice, which promotes dynamic thinning.
3. Merger: Warmer air and seawater temperatures constantly erode the floating ice pack as it moves down the fjord. Towards its end, the ice is less than 100 feet thick in places. Its stability will weaken if warmer water accelerates submarine melting.
Scientists are particularly concerned about a 6.8 mile long and 880 meter wide crack in the floating ice shelf that is approaching the glacier front. If it cracks and becomes a giant iceberg, the lateral drag will decrease for the remaining ice shelf and the interior ice flow and dynamic thinning will accelerate.
RETIRED ALPINE GLACIERS
Glaciers in mountainous regions around the world began to decline at the end of the Little Ice Age (1550-1850) and their retreat has accelerated since 1980. Although it is a minor consideration in the level rise calculations from the sea, retreating alpine glaciers affect the amount of fresh water available for human consumption, agriculture and natural ecosystems. The main types of alpine glaciers are shown below.
Piedmont glaciers from where the glaciers of the valley pour over the plains at the foot of the mountain. An ice lobe (1) extends over the adjacent plain, or piedmont area, under the valley walls of the glacier (2). Much of the glacier’s surface is at low elevation and may show signs of melting.
Valley glaciers are replenished by snowfall all year round in an accumulation zone at the top of a mountain (3). The weight of the ice, the slope, and the gravity combine to slowly push the glacier down the mountain. Sediment and boulders have been pulled into the base of the glacier from a coarse wet “sandpaper”, which carves a characteristic U-shaped valley. Debris called lateral moraine (4) settles on the slopes of the glacier and the terminal moraine (5) is left at its end, or muzzle.
The circus glaciers are the smallest of the Alpine glaciers, varying in size from a few hectares to square miles. They form in a steep amphitheater (6), or circus, and are confined there because their accumulation area (7) is not big enough to collect enough snow to feed an Ice Tongue.
Greenland’s ice loss over the centuries: If the Greenland ice sheet melted, scientists estimate the sea level would rise by about 20 feet.
A team of scientists spent weeks on the Petermann Glacier using state-of-the-art equipment to study the physical characteristics and dynamics.
1. GPS trackers: Several GPS units have been placed at various locations along the glacier. Each tracker records the coordinates of points on the ice over a period of time to measure the flow of the glacier.
2. Radar: Scientists paddled in kayaks along the largest surface meltwater stream in the floating pack ice. They used ice penetrating radar to measure the thickness of the pack ice. The data collected will help researchers determine the rate of thinning of the ice.
Time Lapse Photos: Scientists placed a camera on an adjacent cliff and took pictures of the glacier at various time intervals to record its movement.
ADCP sensor: Sonar that records underwater currents at different depths.
CTD sensor: This 3-foot-long cylindrical instrument was lowered into the icy waters of the fjord to measure the temperature, depth pressure, salinity and density of the water.
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Sources: Dr Alun Hubbard; Daily science; Google Earth and NASA and the New York Times
ILLUSTRATIONS BY JEFF GOERTZEN, AUSTRALIAN GEOGRAPHIC