For Mountains to Grow, Just Add Water


Image from little byte of luck

It's not exactly what you might think. While adding water will speed up the mountains' growth, it's not because the rocks themselves are growing -- rather, it's because extreme rain events help buoy the mountains upwards. As Discovery's Larry O'Hanlon reports, a team of researchers, led by Potsdam University's Andrés Mora, has published a new study examining the impact of rain on Colombia's Eastern Cordillera mountains.
Image from gbaku
How rain events may have influenced the Eastern Cordillera's evolution
Looking through the Andes' mineral and paleo-plant record, the scientists were able to estimate their growth rates over the last few million years. Colombia's mountains, which are characterized by annual rainfall of around 7 meters per year and strong tectonic activity, provided an ideal environment to study the rain-growth relation.

Isostatic rebound
They found that extreme rain events correlated strongly with instances of high growth -- in essence, that the areas exposed to rain were pushed up by tectonic forces at a much faster rate than surrounding ones. O'Hanlon describes the tectonic principle behind it, isostatic rebound, thusly:

Some of the signs of more mountain growth in the wettest area are geological. The lowest layer of rocks - what are often called basement rocks - are a full two kilometres higher up in the rainiest area.

But as fast as the mountains rise, the lashing rains soak and dissolve minerals in the rocks and wash the remains away.

The tectonic principle behind the mountain growth is referred to as isostatic rebound. It is analogous to how a canoe rises up higher when a person steps out of it.

Mountain ranges can rebound upwards in the same way when a load is lifted from their tops.

This, according to Mora, may have influenced the individual mountains' evolution over the past few millions years. Other mountain ranges that may have displayed this climate-tectonics interaction include the Himalayas and the New Zealand Alps.

Mountain growth spurts
This follows an earlier study we reported on, published in Science, in which scientists found that mountains tend to grow in fits and spurts due to a geological process known as delamination:

Conventional theory says that movement of the fluid mantle deep in the Earth slowly erodes this heavy root, allowing mountains to rise gradually . . . She argues that instead of eroding slowly away, the root heats up and oozes downward like a drop of thick syrup, abruptly breaking free and sinking into the hot mantle. The mountains above, suddenly free of the root, then spring up.

Via ::ABC Science: Extreme rain causes mountains to grow (news website)

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