Alps Growing or Shrinking?
Friday, 6. November 2009, 16:36:48
A couple of months ago I wrote about a new hypothesis by Egholm et al. according to which the maximal mountain height correlate closely with climate-controlled gradients in snowline altitude rather than with tectonic activity. In Denmark this hypothesis seems to have lead to a heavy discussion about the uplift/erosion history of the Norwegian mountains between geologists at the University of Århus versus geologists at the University of Copenhagen, and I am looking forward to hear more about this dispute at the Nordic Geological Winter Meeting in Oslo in January.
But how about the Alps? A paper in the latest volume of the science magazine "Tectonophysics" (No. 474, S.236-249) seems now to prove that today's uplifting of the Alps is driven by strong climatic variations. The formation of the Alps through the collision of the two continents Africa and Europe began about 55 million years ago. By now the Alps are shrinking just as quickly in height, as they are growing. Due to the erosional work of glaciers and rivers about exactly the same amount of material is eroded from the Alps as added by uplifting.
Swiss geodesists, who have been measuring the Alps with highest accuracy for decades, have observed, that the Alp summits, as compared to low land, rise up to one millimetre per year. Over millions of years a considerable height would have to result. Researchers from the GFZ German Research Centre for Geosciences have calculated that the mountains eroded concurrently at almost exactly the same speed.
Though the Alps are constantly rising, it is no longer the plate forces but the strong climatic variations since the beginning of the so-called quaternary glacial before approximately 2.5 million years, to which mountain slopes in particular have been reacting so sensitively. To-days rise is attributed to the melting of Alpine glaciers.
Well, today it is probably just a question of isostasy, i.e. gravitational equilibrium between the earth's lithosphere and asthenosphere, meaning that the Alps "float" at an elevation which depends on their thickness and density. The burning question is, why the Alps stopped “growing”, where they did, during their collision phase. Was this only a question of isostasy or was the “snowline effect” at work?
But how about the Alps? A paper in the latest volume of the science magazine "Tectonophysics" (No. 474, S.236-249) seems now to prove that today's uplifting of the Alps is driven by strong climatic variations. The formation of the Alps through the collision of the two continents Africa and Europe began about 55 million years ago. By now the Alps are shrinking just as quickly in height, as they are growing. Due to the erosional work of glaciers and rivers about exactly the same amount of material is eroded from the Alps as added by uplifting.
Swiss geodesists, who have been measuring the Alps with highest accuracy for decades, have observed, that the Alp summits, as compared to low land, rise up to one millimetre per year. Over millions of years a considerable height would have to result. Researchers from the GFZ German Research Centre for Geosciences have calculated that the mountains eroded concurrently at almost exactly the same speed.
Though the Alps are constantly rising, it is no longer the plate forces but the strong climatic variations since the beginning of the so-called quaternary glacial before approximately 2.5 million years, to which mountain slopes in particular have been reacting so sensitively. To-days rise is attributed to the melting of Alpine glaciers.
Well, today it is probably just a question of isostasy, i.e. gravitational equilibrium between the earth's lithosphere and asthenosphere, meaning that the Alps "float" at an elevation which depends on their thickness and density. The burning question is, why the Alps stopped “growing”, where they did, during their collision phase. Was this only a question of isostasy or was the “snowline effect” at work?
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http://www.physorg.com/news176643920.html
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http://www.livescience.com/environment/091105-alps-grow-shrink.html
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http://www.eurekalert.org/pub_releases/2009-11/haog-ata110509.php
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http://www.sciencecodex.com/are_the_alps_growing_or_shrinking
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