Great Sand Dunes National Park
Sand dunes of this size are usually associated with hot arid climates, but the temperature here in the Rockies hardly ever gets above 80degrees, and these dunes receive more than 40” of snow per year. From a distance the dunes seem tiny compared to the towering Sangre de Cristo Mountains behind them, but up close these mounds of sand might as well be mountains themselves. Dunes can reach up to 750ft. above the valley floor and the park contains three mountain peaks that stand over thirteen thousand feet tall.
The dune field contains an estimated 1.2 cubic miles of sand. That’s enough sand to fill over 2.8million Olympic swimming pools.
The San Luis Valley, bordered by the Sangre de Cristo Mountains to the East and the San Juan Mountains to the West is nearly the size of Connecticut. Massive amounts of snow and glacial melt water washed sediment into the valley, and created a large lake that covered most of the valley floor. The lake disappeared after a volcanic dam on the south end of the valley gave way and the lake drained via the Rio Grande, which is the likely cause of the Rio Grande del Norte Gorge. Sands left behind on the ancient lakebed were blown northward by the prevailing southerly winds to the base of the Sangre de Cristo Mountains. It is quite unordinary for a dune field like this to form in a setting like the Rocky Mountains. Sand grains are easily washed down stream, and eventually toward the ocean, so a dead end for water-carrying sediments is needed for sand to stick around. Despite a large amount of runoff coming from the Sangre de Cristo Mountains and the Rio Grande River running through the middle of the San Juan Valley, the two don’t meet and sand carried away by Medano Creek is blown back to the dunes by winds.
