Colorado Sand Dunes
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Wind is one of the great shapers of landscape, and one of the best places to appreciate that is at the Great Sand Dunes National Monument in southern Colorado.

Hi, I'm Dave Thurlow, and this is the Weather Notebook. It's unusual to find sand dunes in the mountains, but Colorado boasts some of the tallest "aeolian," or wind-formed dunes in North America- some rise more than 700 feet above the valley floor. Most of the sand in the dunes was blown there from the other side of the San Luis valley -about fifty miles away. And, as geologist Andrew Valdez explains, the dunes are a result of the way wind interacts with the Sangre de Cristo mountain range:

"Out in the valley there's basically one wind direction sw, so the sand out there migrates towards the NE. But there's a zone a few miles from the mountain front where the wind pattern changes and we get more complex wind directions. We get winds coming over the mountains from the NE and the turbulent flow makes the wind direction vary in just about every direction. Once the sand gets into this complicated zone of wind, then the sand stops migrating because it's not always blown in the same direction, it's blown back and forth in lots of different directions, so that's why these dunes have gotten so big. They've grown vertically instead of migrating."

Valdez says the dunes have been here at least since the end of the last ice age- about 10,000 years. But no one really knows how old they are or how long it took the winds to make them. To find out, scientists will soon take grains of quartz from deep within the dunes into a laboratory to figure out when they were last exposed to light.

We sent producer Becky Rumsey to the Great Sand Dundes National Monument and you'll be hearing more about wind and dunes from her in the coming weeks on the Weather Notebook. Our show is funded by Subaru and by the National Science Foundation.