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:
WIDGETIZE
piombaldo # 12. August 2009, 22:19
Some examples:
1. in Antarctica there are 2 very high mountain ranges, the pratically unknown Gambutseev Range (Ole, say us something about them...!!) and the transantarctic chain, wich is not an orogene but a rifting strucure, if I right remember.
2. the higher ranges are the more recent ones.
3. in this way how can be in Americas Ande and the Rocky Mountains higher than the central america Mountains?
PS: in these days I'm seeing how among the remnants of the European Ercyinian Batholith the higher elevations are reached in Corsica Island (where in winter there is snow....)
nielsol # 13. August 2009, 08:28
There are two main players: 1) uplift rate (mainly tectonic forces) and 2) erosion rate (including glacial), and their relative roles have often been discussed.
A first comment may be that correlation does not imply causation - never the less it is a refreshing thought. The models used in the study do, however, suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces.
What the new idea implies is that the glacial erosion rate will always outweigh the uplift rate, so that the maximal mountain heights depends on the local snow-line - above which glaciers form and do their erosional work. In other words - the Himalayas could not have reached its present height nearer the pole or in a much colder climate.
It is obvious that when uplift stops, the erosion will go on (peneplaning) with all possible erosional forces.
I have of course seen other explanations for the exceptional heights of the Himalayas and certain parts of the Andes - mainly based on plate tectonic processes. What I find refreshing now, is that the question is turned round from “why are the Himalayas so high?” to “why are other mountains lower?” - especially where uplift is still going on. This new idea does probably not supply all the answers, but it may be a step forward towards a better understanding of the whole complexity.
Hopefully a debate follows this publication.
As to the Gamburtsevs - in spite of recent mapping (from the air) too little (to my knowledge) is known about these mountains to draw any valuable conclusions. I have indeed sometimes thought of posting about it, but have decided to wait until I have more and better information. The age (and cause) of the orogeny seems extremely uncertain!
piombaldo # 13. August 2009, 13:31
somehow is the same problem of sedimentary basins: sediments are many kilometers tall but it's not true that sediments now laying several kilometers deep were deposited in this place, vertically speaking.
It could be that if subsidence is a common and well-known event, mountain chains suffer of some types of events (tectonic and erosional) wich we don't know today.
perhaps yesterday evening I was too much tired to understand you...