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Alaska glaciers melt faster than thought

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  • npat1
    Alaska glaciers melt faster than thought By MATT VOLZ Associated Press writer Sunday, September 24, 2006 JUNEAU, Alaska -- Less than 10 minutes after lifting
    Message 1 of 1 , Sep 25, 2006
      Alaska glaciers melt faster than thought
      By MATT VOLZ
      Associated Press writer Sunday, September 24, 2006

      JUNEAU, Alaska -- Less than 10 minutes after lifting off from the
      airport, the helicopter entered the frozen world suspended above
      Alaska's capital.

      Snowcapped mountains rose on either side as the small team of
      scientists and students peered down at a jagged blue carpet of ice
      below. The pilot turned up one arm of Mendenhall Glacier only to find
      the way blocked by a wall of fog. The storm was moving in; the work
      would have to be done quickly.

      Hydrologist Eran Hood used a handheld global positioning system to
      guide the pilot higher up the ice field on a clearer path. Circling
      low, the scientists spotted what they were after: A tiny pyramid of
      wire nearly invisible in the field of white.

      In this lonely corner of an ice field larger than Rhode Island, the
      packed snow crunching under their boots, the group set up shop. They
      were about to find out just how much this part of the glacier had
      melted over the summer and how fast it was moving.
      Hood and physicist Matt Heavner, his colleague at the University of
      Alaska Southeast, measured at least 10 feet of ice loss since May
      there and at two other spots on the glacier.

      Rain was beating down on the tourists at the glacier's terminus below.
      The year's consistently bad weather has been dreary for the visitors,
      but something of a reprieve for the melting Mendenhall Glacier.

      "It's a good summer to be a glacier," Hood said.

      There haven't been too many, judging by the rate at which Southeast
      Alaska's rivers of ice are melting.

      Most of the glaciers stretching from Yakutat Bay to the Stikine
      Icefield, which goes into northwestern British Columbia, are thinning
      at twice the rate that was previously estimated, according to a new
      study co-authored by Hood's mentor, glaciologist Roman Motyka of the
      University of Alaska Fairbanks' Geophysical Institute.

      Comparing radar mapping data from a space shuttle mission six years
      ago with air photos taken between 1948 and 1979, Motyka, UAF colleague
      Chris Larsen and three other scientists pinpointed the extent of the
      glaciers' volume change.

      They found that 95 percent of Southeast Alaska's glaciers are
      thinning. Some glacier surface elevations had dropped as much as 2,100
      feet since 1948, such as the Muir Glacier in the popular Glacier Bay
      National Park and Preserve.

      With the more precise data, they figured the rate of thinning was
      greatly underestimated from the last study done in 2002.

      The scientists calculated that an average of 3.5 cubic miles of
      glacier ice melts each year in the region due to a combination of
      climate change and glacier dynamics. They say even that may be an
      understatement of the actual rate of melting.

      Mendenhall Glacier is a relatively small river of ice compared to the
      rest of Southeast Alaska's extensive network, but it stands out. It is
      Alaska's most visited glacier, drawing 367,000 people to the U.S.
      Forest Service's visitor center last year.

      The glacier is rapidly shrinking up the mountainside -- as rapidly as
      glaciers can, anyway. Visitors who have observed the glacier see the
      change themselves. Motyka estimated that the glacier's terminus will
      pull out of Mendenhall Lake entirely within 10 years.

      Hikers can trek up the side of the glacier along craggy rock that was
      under a deep layer of ice just two years ago. They can poke around in
      ice caves that weren't there at the beginning of the summer -- and
      which will be gone by the season's end.

      "We don't want to spend too much time underneath," Hood said in one
      such cave, as water from the blue roof dripped all around. "These are
      all pretty ephemeral."

      Southeast Alaska's glaciers are very sensitive to climate change
      because of their large surface areas at low elevations. In Juneau, the
      winters have been getting warmer and rainier -- 6.8 degrees warmer
      compared to 50 years ago, according to Laurie Craig, a naturalist for
      the Tongass National Forest.

      Those warmer temperatures can disrupt a glacier's surface mass
      balance, the balance achieved between the melting period of summer and
      accumulation period of winter.

      For many Alaska glaciers at lower elevations, warmer temperatures are
      causing the equilibrium line that separates the accumulation zone from
      the melting zone to rise. Yakutat Glacier, for example, has lost
      nearly all of its accumulation zone.

      "This icefield will likely disappear completely under current
      conditions," the authors of the new study wrote.

      While climate change causes equilibrium shifts and thinning, it isn't
      the only reason Alaska's tidewater glaciers are retreating from lakes
      and the sea. The retreat may be triggered by warmer temperatures, but
      then the dynamic cycle of a tidewater glacier takes over.

      The speed of the glacier increases, drawing down the ice from above at
      a faster rate and increasing calving below. In Southeast Alaska, the
      ice loss at their terminus can cause tidewater glaciers to retreat
      more than half a mile a year -- and that loss can't be directly
      attributed to climate change, the scientists say.

      "Once initiated, these calving losses are largely independent of
      climate change and can be an order of magnitude greater than ice
      losses driven solely by climate change," they wrote.

      Then there are the anomalies. Five percent of the glaciers studied,
      such as the Taku in the Juneau Ice Field, are expanding and thickening.

      Many of these glaciers extend higher in elevation, giving them a
      larger zone where snow can accumulate.

      Glacier dynamics have the opposite effect with these glaciers. Their
      accumulation zones are expanding and their melting zones are
      shrinking. The result is a different kind of imbalance, one that
      causes the glaciers to advance.

      Motyka said scientists will have a better understanding of what has
      happened to the glaciers since the 2000 space shuttle data once new
      photos taken this summer are analyzed. With the last analysis showing
      glaciers melting at twice the rate previously thought, he said he
      expects more of the same.

      "Presumably, things have accelerated," he said.
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