As so often happens, I return to look at the raw files from a photo outing and discover a picture that I had put aside in the initial triage which on second look really appeals to me. Such was the case with this picture of the Mountain of the Sun and the Twin Brothers. The picture was taken on the road to Zion Lodge, upon our arrival at Zion NP, on a beautiful, sunny November afternoon. The sun was shining directly on the rock face of the Twin Brothers and casting shadows in the recesses of Mountain of the Sun. I like the strong contrast between the shadows and highlights and of course, the vibrant red colour of the rock.
Over 200-million years ago the area where Zion is today was a desert basin. Over vast amounts of time the mountains eroded and the material was carried by slow moving streams and rivers to be laid down in the vast basin, filling it with sand. Time passed and the sea covered the dunes as the environment changed. Calcium carbonate cemented loose grains of sand making hard sandstone. It turned the seabed to limestone and mud and clay to mudstone and shale, forming the sweeping diagonal cross-bedding that Zion National Park is famous for.
The basin lowered due to the weight of the deposits. More time passed and the earth shifted and forced the plateau up, slowly and irregularly as the sea drained away. Streams flowed over the edge of the plateau giving them the power to move debris at a great rate. This carved Zion Canyon by vertical retreat of the canyon walls. Oddly, this occurred in an area where the Navajo sandstone was only 2000 feet at its thickest. Today, the North Fork of the Virgin River continues to move debris and erode the canyon, moving an average of 5000 tons of rock fragments daily. Although consistent efforts by the river do some of the work, it is flash flooding that brings the power to make drastic changes. In fact ninety-percent of the carving is from flash floods. A large flood can result in 9000 cubic feet of water per second raging down the Virgin River. The result is that Zion Canyon is getting deeper at a rate of 600 feet per million years.
The rock formations at Zion have been changing for a very long time and are still changing today. Slowly, over vast amounts of time, the great monoliths you see will return to the great sand dunes from where they were born in ancient days. The forces of nature make their way through layers of sedimentary rock every day of our future, just as they have in our past. The largest monolith in the world, the Great White Throne, will slowly crumble into layers of sand.
-Courtesy of http://www.zionnational-park.com