Sea And Sand 720p
LINK ::: https://bytlly.com/2trgDF
The dunes were formed by the right combinations of wind, water, and sediment. Creeks and streams brought in large amounts of sediment and sand into the valley. Wind then blew the sand toward the bend in the Sangre de Cristo Mountains, where opposing storm winds helped squeeze the sand into the tall dunes you see today. While this explanation does answer in the question above, the story of how the Great Sand Dunes were formed is much more complex, and as new research discoveries occur each year, is continually evolving. Below is a summary of what most geologists currently understand to be the broad series of events that took place in the formation of these massive dunes.
After Lake Alamosa drained away, smaller lakes still covered the valley floor, including two broad lakes in the northeastern side of the valley. Large amounts of sediment from the volcanic San Juan Mountains continued to wash down into these lakes, along with some sand from the Sangre de Cristo Mountains. The sediment filling these lakes became the main source of sand for the dunes. Dramatic natural climate change later significantly reduced these lakes, leaving behind the sand sheet. Remnants of these lakes are still found today, in the form of sabkha (alkali flat) wetlands and playa lakes.
As time went on, the wetlands and playa lakes (lakes that grow and shrink periodically with water availability) played an important role in the formation of the dunes. Much of the sediment that had been brought into the valley from the mountains was unsorted, having a mixture of grain sizes and materials, including muds, silts, clays, and most importantly sands. These smaller bodies of water and seasonal lakes helped sort the sand from the rest of the sediment. When the lakes and wetlands are full, sand is deposited near the edges forming little sandy beaches. As water levels lower, the sand is then exposed to wind, allowing the aeolian processes to take over. This created a continual sand source for the growing dunes for quite some time, allowing the dunes to accumulate enough sand to reach their current massive size.
Even with the opposing storm winds, most sand is still blown toward the mountain ranges. Here, two seasonal mountain streams, Medano Creek and Sand Creek, capture sand from the mountain side of the dunefield and carry it around the dunes and back to the valley floor. The creeks then disappear into the sand sheet, and the sand blows back into the dunefield. Barchan and transverse dunes form near these creeks. Water from these creeks then reappear in near the southwestern edge of the park, feeding into the wetland and playa lake systems. Learn more about the hydrology of Great Sand Dunes.
This combination of opposing winds, a huge supply of sand from the valley floor, and the sand recycling action of the creeks, are all part of the reason that these are the tallest dunes in North America. There are other dunes in Colorado, and in most western states in the US, but none as tall (741feet/ 226 meters) and none as dramatic. Here giant dunes rise in front of the alpine Sangre de Cristo Mountains, while streams flow across the sand seasonally, making for an unusual and unexpected sight. 1e1e36bf2d