Hydrology of Great Sand Dunes National Park
Without an active water cycle within the park, the sand dunes would have vanished long ago.
Without an active water cycle within the park, the sand dunes would have vanished long ago. In addition to recycling windblown sand off the mountains back into the dune system, water acts as the glue holding the entire ecosystem together. Just under the sandy surface, a large aquifer extends throughout the whole park. In fact, streams like Medano Creek and many of the lower wetlands are visible parts of the top of the aquifer. This is possible because there is a layer of clay-sized sediments, called a perched layer, with a permeability low enough that water cannot flow through it. Without this layer, the water table would be so much lower that much of the vegetation in the park would not be able to survive. Throughout the year, the aquifer rises and falls due to the runoff from the mountains and the high permeability surface sand layer. The water runoff eventually filters through the ground into the aquifer which means that it never reaches a body of water that can take it to the ocean. This closed hydrologic system, also known as an internal drainage system, keep the aquifer stable through dry points of the year and keeps the sand above it full of moisture. This moisture acts as an adhesive for the sand making it stick together instead of continuously blowing away in the wind, and is a source of nutrient-rich water for plants that call the sand fields home. To see this for yourself, dig underneath the first few inches of sand and you will quickly find cold, damp sand lying underneath the sun-baked top layer.
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