Friday, March 15, 2013

View from Angel's Landing, Zion National Park (Utah)

A strenuous, 8 kilometer hike will take you to this stunning view overlooking Zion Canyon atop Angel's Landing in Zion National Park. Towering canyon cliffs stand around the valley, as the Virgin River winds itself through the canyon floor.

The genesis of these cliffs lies in the deposition of sand 240 million years ago. Zion was originally adesert basin, but as surrounding mountains underwent natural erosion, sand was produced. Rivers around the basin transported the sediment, depositing it into layers. Sedimentation occurred, and sand eventually overtook the water-covered basin, turning it into a basin of not water, but sand. Stratum upon stratum of sand layered atop one another over millions of years.

This resultant sand began to undergo lithification and compaction into rock via the filtration of mineral-rich water. Aqueous iron oxide, calcium carbonate, silica, and other minerals helped to turn sediment into sandstone, limestone, and other rocks. Uplift caused the rock to rise further out of the ground, raising these large piles to an elevation of 3000 meters, and still rising today.

Then how are these canyons and steep cliffs formed? Erosion! The Virgin River in Zion is the chief waterway responsible for this erosion. 90% of erosion comes from flash flooding, rather than normal water flow. This erosion carved the preliminary, historic canyon walls of Zion, continuously widening it.

The wide canyon and steep cliffs you see in this image are results of this historic process - sedimentation, lithification, uplift, and erosion. Today, over 4,500 metric tons of rock are stripped of the canyon walls by the Virgin River every day! In combination with the more significant flash flooding, the depth of the Zion Canyon is expected to decrease by 183m (600 feet) in a million years, or 0.18 millimeters per year.


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