Why are Some Mountains so Low?
Wednesday, 12. August 2009, 19:33:40
There are indications that the general height of mountain ranges is directly influenced by the extent of glaciation through an efficient denudation mechanism. A global analysis of topography shows that variations in maximum mountain height correlate closely with climate-controlled gradients in snowline altitude rather than with tectonic activity.
A new study, published in the journal Nature of 13 August 2009, used radar images of Earth's surface (taken during a NASA space shuttle mission several years ago) and computer models to show that glacial action, governed by climate, is responsible for the height differences in many of Earth's mountain ranges. Glaciers carve mountains down near the poles, while in the tropics, mountains are able to rise much higher in the air.
If the snowline altitude is very high, the glacial buildup will be limited and so little of the mountain will be ground down. On the other hand, if the snow-line altitude is much lower, as is the case nearer Earth's poles, the glaciers will effectively grind the mountain away. So in order to get really high mountains you need a high snowline altitude, otherwise glaciers will basically destroy the mountain at elevations below that.
In the Himalayas the snow-line is nearly at a height of 6.000 metres. In the Alps the snow-line lies at around 3.500 metres, and in Norway the snow-line is at 1.500 metres.
The authors don’t think that it is a coincidence that the high mountains exist around the equator, where the snowline is high. The forces of plate tectonics are still pushing up the crust under high-latitude ranges, but the mountain tops just get removed as quickly by glaciers as they accumulate by plate tectonics.
This way the glacial action explains why in a range like the Andes, which runs north to south, the northern mountains are higher than the southern — glacial action has worn down the southern peaks (because they are at higher latitudes in the southern hemisphere).
If the climate stays warmer for many thousands of years, mountains might become slightly higher.
Reference:
Egholm et al.
Glacial effects limiting mountain height
Nature 460, 884-887 (13 August 2009)
doi:10.1038/nature08263
In Danish:
A new study, published in the journal Nature of 13 August 2009, used radar images of Earth's surface (taken during a NASA space shuttle mission several years ago) and computer models to show that glacial action, governed by climate, is responsible for the height differences in many of Earth's mountain ranges. Glaciers carve mountains down near the poles, while in the tropics, mountains are able to rise much higher in the air.
If the snowline altitude is very high, the glacial buildup will be limited and so little of the mountain will be ground down. On the other hand, if the snow-line altitude is much lower, as is the case nearer Earth's poles, the glaciers will effectively grind the mountain away. So in order to get really high mountains you need a high snowline altitude, otherwise glaciers will basically destroy the mountain at elevations below that.
In the Himalayas the snow-line is nearly at a height of 6.000 metres. In the Alps the snow-line lies at around 3.500 metres, and in Norway the snow-line is at 1.500 metres.
The authors don’t think that it is a coincidence that the high mountains exist around the equator, where the snowline is high. The forces of plate tectonics are still pushing up the crust under high-latitude ranges, but the mountain tops just get removed as quickly by glaciers as they accumulate by plate tectonics.
This way the glacial action explains why in a range like the Andes, which runs north to south, the northern mountains are higher than the southern — glacial action has worn down the southern peaks (because they are at higher latitudes in the southern hemisphere).
If the climate stays warmer for many thousands of years, mountains might become slightly higher.
Reference:
Egholm et al.
Glacial effects limiting mountain height
Nature 460, 884-887 (13 August 2009)
doi:10.1038/nature08263
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http://www.nature.com/nature/journal/v460/n7257/full/nature08263.html
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http://www.livescience.com/environment/090812-climate-mountain-height.html
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http://news.yahoo.com/s/livescience/20090812/sc_livescience/climatecontrolsmountainheightsnewstudyshows
In Danish:
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