July 8, 2008 -- The more it rains on some mountains the faster they grow, say geologists studying the fault-riddled, intensely rainy Eastern Cordillera of Colombia, South America.
This discovery has nothing to do with water actually growing rocks and everything to do with how mountains buoy upwards when extreme rains scour away the summits.
Using mineral and paleo-plant data, researchers have now measured high growth rates of Columbia's northeastern limb of the Andes. They show that the area which has been exposed to the heaviest rains on the planet also reveals signs of having been pushed up by tectonic forces at a much faster rate over the last few million years than surrounding areas.
"The Himalayas, the southern and central Andes, and the New Zealand Alps are premier examples of (mountain ranges) where interactions between tectonics and climate have been documented and where the interplay between them may have fundamentally influenced the evolution of individual mountain ranges...," report Potsdam University's Andrés Mora and his colleagues in the July/August issue of the Bulletin of the Geological Society of America.
"In the northern Andes, where strong precipitation gradients also exist, such relations have not been explored," Mora writes.
Strong may be an understatement for the rain there. The mountains get in the way of some very wet, easterly air. The mountains cause that wet air to rise, cool and rain out a veritable deluge.
The researchers report that the annual rainfall comes to about 275 inches (seven meters) per year -- the highest on Earth in their study area. This, plus the active upward thrusting faults, make this part of Columbia the perfect laboratory for watching how climate affects mountain growth.
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 kilometers higher up in the rainiest area. But as fast as the mountains there 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.
"The potential of climate to influence tectonics on a regional and continental scale has been widely theorized over the past 15 years, but studies that demonstrate just how this occurs have been rare," commented Earth scientist Peter Koons of the University of Maine in Orono.
"We have known that, at the large scale of the Himalayas or the Southern Alps, climate and tectonics interact in fundamental ways, but the lower limits of that interaction, where information on the mechanisms of interaction still remains, have been very elusive," Koons explained to Discovery News.
By using a broad range of methods, Mora and his colleagues have teased out how the regional growth of one of the largest mountain belts on Earth has been heavily influenced by exceptional precipitation.
"This is a real advance," said Mora.
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