Geology is all around us, scarcely thought of as we go about our lives. Yet, it affects everything we do as a civilization, as a society and as individuals. While barely appearing to change from day to day, it works to alter the course of evolution. Preserving a record of creatures and landscapes both ancient and forgotten, the story of our past is written in stone and waiting to be read. I offer a view of how I see our world and its inhabitants, both past and present, as seen through my lens.
Saturday, January 29, 2011
Bryce Canyon: Visit It Before It's Too Late
Canyon in southern Utah is eroding quickly, almost right before our eyes at 2-4 feet every 100 years, give or take. The agent of erosion is water, mechanically scouring and abrading with its load of rocks, and chemically dissolving the bedrock, aided by the very steep gradient at Bryce. But water acts in another way to pry rocks apart, one that we seldom think of, by freezing.
In a wet environment, and especially one that has numerous freezing and thawing cycles like Bryce (over 275 per year) with its high elevation, water penetrates every available crevice, both big and small. When water freezes, it expands its volume by about 9%, and in so doing, it becomes a powerful force in the process of erosion by literally breaking rock apart, grain by grain. This is called frost wedging.
The spires and hoodoos, ridges, columns and pedestals, shear walls, and labyrinth of box canyons of Bryce have weathered into a distinctive landscape by the combined action of its rock type, geography and climate. The badlands topography of Bryce is carved into the pink, red, orange, tan and white sedimentary rocks of the Eocene Claron Formation, mainly the Pink Limestone Member. This interbedded, fine-grained limestone, calcareous mudstone and fine-grained sandstone member was deposited in a low-energy fluvial (river and stream) and lacustrine (lake) environment.
The Claron Formation is a rock structure that is weakly held together and especially susceptible to erosion. Geologists say it’s poorly lithified. As the canyon continues to erode to the west, it will eventually capture the watershed of the East Fork of the Sevier River. Once this river flows through Bryce, it will dominate the erosional pattern, replacing Bryce’s amphitheatre with a "V" shaped canyon and steep cliff walls typical of the weathering and erosional patterns created by flowing water. That will likely further serve to enhance Bryce's erosive demise!
Interestingly, the source waters that deposited the Claron Formation originated from headwaters located in the Sevier and MogollonHighlands to the south and west, formed during the Late Cretaceous to early Paleogene. These mountain ranges have since eroded away but could only have reached their destination at the inland system of adjoining basins in Utah had the Grand Canyon not yet formed, which would have acted as an impediment to northeast flow. This implies, assuming the correctness of this scenario, a later period of “drainage reversal” for this portion of the Colorado River system. It also begs the question of “how much of the modern drainage configuration could be inherited from these Paleogene drainages?” (please read Carving Grand Canyon by Wayne Ranney for an excellent presentation of this concept).
For all these reasons, Bryce may be gone before you know it, in perhaps 3,000,000 years, give or take. A very short time, geologically speaking.