Tuesday, September 25, 2018

Utah- the land of cowboys and fairy chimneys

A road trip that's called the Grand Circle and promises cliffs, canyons, and mountains, all bathed in a kaleidoscope of colors. Sounds too good to be true? That's Utah. Describing five national parks and one Navajo Reservation in a ten minute read is a bit much. Therefore, this blog is dedicated to Monument Valley and Bryce Canyon National Park.

Monument Valley is immediately recognizable to most moviegoers. Forrest Gump ran through it, the Transformers stomped their way across, and of course the valley was immortalized by the Western movies where cowboys rode off into the sunset. The valley lies within the Navajo Nation Reservation, the largest land area that is retained by a Native American tribe. 

Nothing like a sunset picture to act as clickbait.
Buttes in Monument valley. Buttes are isolated hills that are characterized by steep sides and a flat top. The red color is due to iron oxide (that also causes rust).

Monument Valley was once covered by sandstone, rocks characterized by sand-sized fragments and minerals. The different rock layers, which were deposited several hundred million years ago, were subjected to erosion by wind, water, and varying temperature. The resulting structures show a large variation because the hard rocks eroded more slowly compared to the soft ones.  

This variation is particularly prominent in the buttes that are peppered around the valley. The lower most layer, Organ Rock Shale, forms "erosion skirts". This easily eroded layer was formed from river sediments carried down from the Rocky Mountains. Above this layer is the erosion-resistant de Chelly Sandstone, formed by windblown sand. The sandstone protects the Organ Rock Shale from eroding further. The top most layer and the steep vertical sides of the buttes are covered by a highly resistant conglomerate of coarse-grained sandstone and pebbles. 

                              
Different rock layers in Mitten Buttes.

Travel 440 kilometers north-west of Monument Valley and you will notice that the theme of erosion manifests itself differently in Bryce Canyon National Park. Here, the unique rock formations are carved by a collaboration of water, ice, and gravity. A vast seaway deposited sediments in Bryce Canyon 144 million years ago. The repeated cycles of invasion and withdrawal of this seaway resulted in sediments of varying composition. Continuous erosion for another 20 million years formed shallow, broad basins which contained iron-rich sediments. 

Hoodoos in the basin. What are hoodoos you ask? Read on..

The distinguishing feature of Bryce Canyon is that it has the largest concentration of hoodoos in the world. Also known as fairy chimneys, hoodoos are thin, tall pieces of rock that protrude from an arid basin. Hoodoos consist of soft mudstone or poorly cemented sandstone topped by hardier, less eroded stone such as compact sandstone or limestone. Furthermore, the erosion-resistant hoodoo cap presses downwards giving the base the strength to resist erosion. 

Unlike buttes, which are predominantly carved by wind, hoodoos are sculpted by water and ice. In the summers the slightly acidic rain dissolves the overlying limestone, giving hoodoos their lumpy outlines. The cracks in the resistant layer also allow the underlying soft rock to be washed away. In the winter the melting snow seeps into the cracks and freezes at night slowly making them wider. The result: a totem pole-shaped body of variable thickness. 

How do hoodoo? 

The landscape of Utah is a breathtaking lesson in erosion. The arid backdrop serves as the perfect background to the imposing rock formations that have been steadily created over a hundred million years. I highly recommend heading over if you want to see Nature working its Michelangelo. 

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