The Great Sand Dunes are in Alamosa County in Colorado. They are the largest sand dunes in North America…funny huh? I figured sand dunes would be around a beach, but not necessarily. They are colossal, breath taking, and terrifying all in one!
The dunes formed less than 440,000 years ago…it is unsure the exact age. They began forming when the breaking apart and movement of large plates on Earth’s surface, the Sangre de Cristo Mountains were raised in the rotation of a large plate. The San Juan Mountains were created through long and violent volcanic activity. The formation of the two mountain ranges left the San Luis Valley. Sediments from both ranges filled the deep chasm of the valley, along with water from various streams and rivers. At one time, a large lake now called “Lake Alamosa” covered the floor of the San Juan Valley. Over time and climate changes, the lake evaporated and escaped to the Rio Grande River. This left large sand deposits. The sand blew with the southwest winds toward a low curve in the Sangre de Cristo Mountains. The wind funnels toward three mountain passes, The Mosca, Medano, and Music Passes and the sand accumulates in this pocket. The winds blow from the floor of the valley, but during the storms, the wind blows back…this allows the dunes to grow vertically. They cover approximately 19,000 acres, and rise about 750ft off of the San Juan Valley floor.
The Great Sand Dunes National Park is definitely a sight to see. I went this summer and it is just breath taking to look at. However, nasty storms pass through there. The dunes are often struck by lightening so when a storm comes they urge everyone to get off. And yes, the public is allowed to go out and climb them. We were there for about an hour and 2 storms came through within that time, they are short, but violent. We were watching the lightening just strike and hit the dunes everywhere, it was neat, but it also reminds you of how powerful mother nature can be, both good an bad.