Sunday, September 28, 2008

Slot Canyons, Canyons, Moqui Marbles, Geology Heaven - a report by Jake

I just got back from the most amazing trip to the Grand Staircase. We went hiking in the slot canyons called Peekaboo, and Spooky. While hiking down there we walked on a huge rock outcropping of sandstone, and I observed the water weathering the rock as it ran down. As we got to these canyons I was able to recognize all the steps that it would take for a natural bridge to form, starting with potholes and flood after flood. It was neat. Going through Spooky, I realized why it was so spooky it got so narrow that we had to walk sideways to fit through it. There were moqui marbles being uncovered everywhere. It was neat to see the principal of how resistant some rocks are compared to others and see that these iron based stones were more resistant so they stuck out of the walls. Sat and pointed out all the things i have learned to the class and taught them about everything from differential weathering to how the Navajo sandstone came to look the way it does, i.e. layering. On the way back up that outcrop of rock I mentioned earlier I saw recognized that the weathering that was happnening where the water was running down the rock was actually the beginning of a baby slot canyon!!! HOW COOL IS THAT?!?

Next we went to the Box of Pine Creek canyon just north of Escalante, and I started was in heaven again being able to look at all the layers, and finding all sorts of rocks. This place had only a alot of igneous rocks and Sedimentary. It was way cool to see how much I have learned from that field trip and a few weeks of class. I think my class got sick of me pointing out all of the cool facts to them. We stopped at the Devil's garden and looked at the HooDoo's there. with the natural bridges. I even taught my class the difference between them. And of course I was pouring acid on every thing:) I had my eye lens and also had my piece of glass so I could clasify.


Thursday, September 25, 2008


Springs form when water seeps through the overlying layer of sandstone (Slick Rock). Sandstone is a permeable layer of rock meaning that water can flow throughout the rock. When the water reaches a layer of shale which is non-permeable,meaning that water cannot pass through (Dewey Bridge), it follows the contact between the two layers until it escapes. While the water flows between the contacts, it is eroding the rock that it flows through. As the water flows along the contact between the Slick Rock and the Dewey bridge, the Dewey Bridge is eroded. This leaves the Slick Rock with no support underlying it. The result of this is the slick rock collapsing. Small cave-like structures are formed, much like that in the picture. Water continues to flow through the sandstone and along the contact between the two layers. As a result of the water and the loose sediment, vegetation is able to grow.  

The Entrada Formation

The Entrada Formation
The Entrada formation was deposited in the middle Jurassic and is about 175 million years old. The Entrada formation is divided into three members. The bottom layer is known as the Dewey Bridge Member. This layer is directly below the Slickrock Member and consists of brick-red silty sandstone that forms crinkly beds. The middle layer is known as the Slickrock Member. This is the first layer that is visible in the picture (uppermost layer in picture) and is characterized by red cross-bedded sandstone that is responsible for forming cliffs and the world famous arches in Arches National Park. The uppermost layer of the Entrada is the Moab Tongue, which is made up of white cross-bedded sandstone (this is not present in this picture). 

Wednesday, September 24, 2008

Differential Weathering

This is a picture of Balanced Rock in Arches National Park. We came here on day two of our field studies trip and we stopped at the view point for balanced rock. It is great picture of differential weathering. Differential weathering is the process where the harder rock is worn away less rapidly than the softer rock. With Balanced rock the big bolder that that is balanced is part of the Slick Rock layer (sandstone) and the pillar that is balancing it of the Dewey Bridge layer (shale.)The Shale erodes away faster than sandstone because of its composition of clay is easily eroded away by water. The sandstone is more resistant because of the quartz in it. That is the reason why the Dewey Bridge Shale is eroding away faster than that of the Slick rock sandstone. With Balanced Rock in this picture the Dewey Bridge is weathering faster and it breaks apart and crumbles leaving the Slick rock standing on a smaller than its self pillar. Slowly the Dewey Bridge will weather away completely and the Slick Rock bolder will fall because of gravity. Isn't amazing how weathering forces create such beautiful features?

Sunday, September 21, 2008

Formation of Fins in Salt Valley Anticline

Standing on the edge of the Salt Valley Anticline we looked at the depression that had been created by rising salt deep below the earth’s surface within the crust in the Paradox Formation. As it rises it pushes on the layers of rock and sediment above creating a dome like hill on the surface. Big cracks called Joints begin to form and allow water to drain down to the salt level and dissolve the salt. As it dissolves it leaves unsupported space below the other layers, and gravity helps to collapse parts of the upper layers. In Arches National Park, which is part of the S.V.A. We stopped at the Park Avenue Trail Head and Renee continued the story.
The picture is of the Park Avenue Trail Head courtesy of Scott Frost. As the ground collapses it falls in between these joints that were created previously, leaving these gigantic walls of rock. The rock shown here is two different layers, the top, smooth rock is calld the Slick Rock Formation, and underneath it, the more ‘bricky’ looking layer is known as the Dewey Bridge.