The researchers also found that the ocean floor is barren of sediment where the Andes have their greatest height. Whereas in northern Peru and southern Chile, where the Andes are half as tall, the fault is much more slippery and the ocean floor is thickly covered in sediment. The pair concluded that ocean floor sediment acts like a lubricant.
"The sediment is sloppy, wet, and weak, it's like adding oil to the subduction zone," said Lamb. "In those lubricated parts you'll never get high mountains because you can't hold them up."
The amount of sediment washed to the ocean floor is controlled by how much rain and snow falls on the mountains. Wetter regions like southern Chile have large rivers that carry debris down into the ocean. No rivers gush down from the much drier central Andes.
According to Lamb, the reason the west coast of central South America is so dry is because the so-called Peru-Chile current brings up unusually cold water from Antarctica.
"This cold water mass actually plays a major role in keeping the climate along the coast dry," he said. "It suppresses formation of rain clouds, so you get almost no rain forming in this area."
This cold current is related to the general cooling of the global climate over the past 50 million years or so. According to the researchers, the rise of the Andes closely follows this cooling trend.
When the global climate began to cool about 50 million years ago, the ice sheets on Antarctica were small and the west coast of South America was at or below sea level.
By 40 million years ago, the Antarctic ice sheets had begun to grow and the Andes began to rise, said Lamb. When the ice sheets rapidly expanded about 14 million years ago, they caused the Peru-Chile current system to cool sufficiently to dry out central South America, starving the ocean floor of sediment.
"Once starved of sediment, the ocean floor became rough and sticky and suddenly you had forces available to stick up the mountains," said Lamb. "So, climate change can trigger mountain building."
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