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Earth Science

Glaciers Protect Alpine Peaks From Erosion 29

Posted by Soulskill
from the just-put-a-tarp-over-it dept.
Hugh Pickens DOT Com writes "BBC reports that French scientists studying erosion on Mont Blanc have discovered that glaciers shield summits from erosion, acting as a protective lid and playing little part in erosion. In contrast, water and rain eroded glacier-free areas 10 times faster than areas protected by the glacier. These results may explain the high altitude of the Alps. Driven by the tectonic collision of Europe with Africa, the high alpine bedrock is rising about one millimeter each year. Glacier-free areas of the Alps erode at a similar rate but where the mountains are protected by ice, the peaks wear away at one tenth that rate. A long-term effect of this might be a rise in the maximum altitude of the Alps. 'However, mountains don't grow to infinity, so there must be another mechanism which has lowered the summit of Europe,' says Fritz Schlunegger. 'According to (Dr) Godon's findings, this erosion is not related to glaciers, so we still have to think about other possibilities.' Around the globe, mountain glaciers — especially those at low latitudes — are retreating in response to climate change. The glaciers around Mount Everest have lost more than one-eighth of their area in the past 50 years, and the snowline had retreated 180 meters up the mountain sides. The results suggest that changes like these could change the shapes of the world's highest mountains, and that climate and mountain landscape are intimately linked."
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Glaciers Protect Alpine Peaks From Erosion

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  • Surprising (Score:4, Insightful)

    by timeOday (582209) on Saturday August 03, 2013 @02:02PM (#44466083)
    I have always been told the jaggy, sawtooth peaks in glacier areas were caused by the continual cutting action of glaciers sliding downhill. (Then again, maybe that is still true, just 10x slower than being exposed to the elements).
    • Re:Surprising (Score:5, Informative)

      by PPH (736903) on Saturday August 03, 2013 @02:36PM (#44466219)

      Most of the weight of a glacier sits on the flanks of the mountain. That would be the area scrubbed by the movement of the glacier*. The ice/snow on the peaks is thinner and relatively stable. So the effect of a glacier-covered mountain is to have its flanks carved away, making it 'pointier'. This will continue until the slopes become so steep that the shape is no longer structurally stable. An ice-free mountain would probably erode uniformly from top to bottom and its resulting shape would be different (probably rounder on top).

      *Increased melting rates causes glaciers to move faster, also accelerating the rate of mountain flank erosion.

    • by icebike (68054)

      Except you have lots of jaggy sawtooth peaks where there are NO glaciers [wikimedia.org] and U shaped valleys where there are glaciers [thinkquest.org].

      As for mountains eroding at a millimeter per, I'd like to know how they calculated that. If they simply measure the sediment in melt water and extrapolate that to cubit meters of rock and spread it over the entire watershed they would find that glaciated areas drop a lot more sediment [ingentaconnect.com] than non-glaciated areas.

      On the other hand if they are doing actual height measurements, how do they arriv

  • by symbolset (646467) * on Saturday August 03, 2013 @02:15PM (#44466129) Journal
    Most of the area of these glaciers is less than 13,000 years old. On the level of erosion of mountains, not significant. The glacier cover is quite new on this scale of time.
    • by swillden (191260)

      Most of the area of these glaciers is less than 13,000 years old. On the level of erosion of mountains, not significant. The glacier cover is quite new on this scale of time.

      Just what I was going to say. The summary is conflating massively different time scales. Just because both of them are far longer than our lives doesn't mean they're the same.

    • by khallow (566160)
      Ok, the article says that peaks covered by glaciers eroded ten times as slow. If a peak is uncovered by interglacial periods a tenth of the time, then it still receives roughly just as much erosion from the interglacial periods as it does during the glacial periods and erodes about twice as fast as a mountain that is always covered by glaciers. That is significant on the time scale of millions of years.
    • by riverat1 (1048260)

      Most of the area of these glaciers is less than 13,000 years old.

      I'm trying to understand where you get that statement from. Are you saying those areas were not glaciated during the last ice age (from ~100,000 years ago to ~13,000) years ago? I'm pretty sure they've had glaciers there during all of that time. It may be that the oldest ice in some of them is only 13,000 years old but that is simply a function of the fact that glaciers flow, they get new snow which becomes ice at the top and as it reaches the bottom it melts out.

    • Sorry to rain on your parade, but the mountains are way older than 13000 years. Maybe you are referring to the ice that's on them? There has been ice on them much longer as well. It's just the current layer of ice that isn't that old, due to the fact that it erodes and slides down the mountain. I doubt the age of the current bits of frozen water is relevant to how much it protects the mountain side from wind and sun erosion, it will be the fact that it's covered that matters.
    • by hawkfish (8978)

      Most of the area of these glaciers is less than 13,000 years old. On the level of erosion of mountains, not significant. The glacier cover is quite new on this scale of time.

      Cite? Otherwise, I have no clue why this is modded +4 Insightful...

  • FTFA - "Glacier-free areas of the Alps erode at a similar rate but where the mountains are protected by ice, the peaks wear away at one tenth that rate."

    "Protected by ice" != "glacier"

    Former glacial valleys, like in the UK looking down the A5 from Llyn Ogwen north-west towards Bethesda, are clearly far more eroded than the adjacent ridges. The valley is a huge U-shaped gouge, straight through the surrounding mountains,.
  • Cause the Alps to crumble away? Are humans to blame for destroying them?

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