Скачать или смотреть Sedona, Arizona, Why Are The Rocks Red?

In this video, Dr Robin Weeks, whose background is in geophysics, continues his fascinating playlist about the landscape of Sedona, Arizona, one of the most visited sacred spots in the world.

Sedona is located in the Upper Sonoran Desert of Northern Arizona, and is located just at the base of the Mogollon Rim, as escarpment that runs through the middle of Arizona for around 200 miles. It is the forces of erosion at work in this area that gives Sedona is spectacular rock formations.

Robin has found over his years hiking in this beautiful place that one way of entering deeper into a relationship with it is to become informed about the processes that formed it. Given his training as a geophysicist, he is ideally placed to offer us a brief guide to that well-worn question: why are the rocks red?

The answer to that lies back in the Permian Period when this area was a shallow, warm sea near the equator. Over many millions of year, the bed of this sea formed sedimentary layer after layer. Later, the grains of quartz crystals that compose sand were washed in deposits of iron oxide, hematite, and thus Sedona’s red rocks became red. This crimson sandstone is known as the Schnebly Hill Formation and is 800 to a 1000 feet thick.

One of the most striking features of this landscape the effect is how layers of cream sandstone contrast with layers of red sandstone. Standing in front of a fine example of this, Robin describes how the cream layers were formed later, and under different circumstances during the Aoelian Era. At that point, as the Pedregosa Sea finally retreated, 265 million years ago, a 500 to a 1000 foot layer of cream sandstone was formed from sand dunes. Slightly larger grain size allowed for a freer passage of water through the sand, washing it clean, and leaving it with the colouration it has now.

Robin makes the point that one of the great, defining features of this landscape is the impact of hundreds of millions of years of geologic time. In Sedona, the relationship between time, rock and desert inhabitants is clear in a way that urban or manmade environments often obscure. Allowing ourselves to contemplate the great sweep of Earth’s history that is laid bare here is yet another way in which we can deepen and strengthen our relationship with the land.