Thursday, June 30, 2011
The Green River is very strange. Unlike most rivers, the Green goes straight though the Uinta Mountains instead of going around this enormous obstacle. The process that created this phenomenon began about thirty million years ago. At the time there was a Northern Green River that flowed east from the Uinta Mountains, and a Southern Green River that flowed south. Over the course of a few million years the Uinta Mountains were eroded creating what is called the Gilbert Peak Erosional Surface. On this erosional surface layers of sediment were deposited that are today called the Bishop Conglomerate and the Brown’s Park Formation. At the same time the southern Green River drainage was eroding faster than the northern Green River. The flat surface of the eroded and covered Uintas and the steeper gradient of the Southern Green river made it possible for the southern Green River to capture the northern Green River. The two rivers combined and began to flow over the eroded Uintas. Then about 10 million years ago a geological phenomenon called uplift raised the Uinta Mountains. This renewed uplift in the Rocky Mountains caused the Green River to cut right into the folds of the Uinta Mountains, thus creating the present landscape. This is called superimposed drainage. Without our knowledge of geological history it would have seemed impossible for the Green River to have its current course. The diagram below shows the changes in the Green River’s drainage north and south of the Uintas over this period of time:
Wednesday, June 29, 2011
As the discharge decreases, the velocity will decrease too. This will cause the river to drop its sediment load – the larger and heavier particles first (like sand) on the sides of the stream forming what river-runners call a beach. The diagram below shows how beaches were built from an artificial flood in the Grand Canyon in 1996.
The diagram shows the river before the flood (March 28) and after the flood (April 1). Notice that after the flood the channel is deeper because the faster moving water scoured the sediment away. This scoured sediment is then left on the side of the river in the area labels deposition – VOILA! A beach…like the one you see in the picture below.
Riverine beaches will erode over time and the sand will end back in the river channel. New floods (periods of high discharge) will scour the channel again and re-deposit sand on the sides.
The discharge level of the Green River was unusually high this year. There was a lot of precipitation this year. The snow that fell even late this season was melting making the river’s discharge extra high. This high discharge may be restoring some beaches. We'll have to see after the discharge decreases later in the season.
I think that beaches are a cool way to see what the river really did. It’s cool that the river is able to pick up and carry that much sediment. I also think it is cool that in a number of years down the line, that the beach you stand on one day could be gone. A new beach might take its place, but it would be all new sediment.
On our first night of our river trip we stayed on a beach. It was fun to walk around with no shoes on because you don’t have to worry about stickers or pointy objects cutting your feet. You could lie down and feel the warmth of the sediment. We also could dig down and bury each other in the warm sand. And that is why I like beaches.
Tuesday, June 28, 2011
Renee Faatz June 2011
The geological history of the Green River is quite interesting. It all started about 1 billion years ago, in the Precambrian era. I will point out some of the highlights of the geologic history of the area.
1. The Uinta Mountain Group was deposited about 1000 million (or 1 billion) years ago
2. The Uinta Mountain Group was tilted and eroded away to make an angular unconformity.
3. The Cambrian period (about 550 million years ago) came next where the Lodore Formation was deposited into a shallow sea
4. Erosion occured and wiped away almost 200 million years of history. This is called a disconformity.
5. Magma intruded into the crust to form a dike about 483 million years ago.
6. The Mississippian Madison limestone was deposited on the eroded Lodore formation (about 350 million years ago).
7. Sand dunes formed the Pennsylvanian Weber sandstone.
8. A shallow tropical sea formed the limestone and phosphorite of the Permian Park City formation.
9. Streams deposited the upper Triassic Chinle formation on a eroded Moenkopi.
10. The Glen Canyon sandstone formed from sand dunes in the Jurassic era (about 180 million years ago).
11. Rivers and lakes deposited the Morrison formation which includes dinosaurs in the Jurassic. This layer contains the dinosaur fossils that make Vernal famous.
12. The Cretaceous period ended about 65 million years ago. The interior seaway that reached the area in this era flooded, which led to the depositing of the Dakota, Mancos, and other layers. These layers were all deposited before the Uintas were formed.
13. The Uinta Mountains formed as part of the Laramide Orogeny which built the Rocky Mountains between about 60 and 30 million years ago. All the rocks previously mentioned were arched up and faulted. The Uinta Arch, Mitten Park Fault, Island Park Syncline, Split Mountain Anticline formed at this time. (Although, Split Mountain was not a split yet).
14. About 30 million years ago the Uinta Mountains were almost completely eroded away. This is called the Gilbert Peak Erosion surface.
15. Between 28 and 12 million years ago streams deposited the Bishop Conglomerate and Browns Park Formation. These sit on an angular unconformity.
16. About 10 million years ago, uplift of the Colorado Plateau and Rockies began to elevate the area. This caused the Green River and its tributaries cut down into the rock causing rejuvenation.
17. Pleistocene glaciers created the landscape of the high Uintas. Higher stream flows deposited gravel terraces like the ones we saw at Island Park.
18. The Green River and its tributaries eroded to create the landscape we see today.
As number 18 says erosion and deposition created the amazing landscape we saw on the trip. The landscape along Green and Yampa Rivers are great examples of geologic processes. This is a very cool thing to look at. I really recommend going on a river trip and looking at the mountains and other formations and seeing first hand what they look like. The rapids are a blast, they feed you well and even just floating down the river is nice and relaxing.
Topography also plays a major factor determining where rapids are formed. It is generally consistent over time. Increased flow that happens during heavy rain fall or flood season can alter the stream bed permanently by depositing rocks in different places or by creating new channels for flowing water. Along the Green River we went along many Rapids. Some of them were: Disaster Falls, Hells Half-Mile, and Triplet Falls. The rapids along the Green River area are classified based on the magnitude of the rapids. The ones we encountered ranged from Class 1-4. If you're in need of a good time, visit the rapids of the Green River in the canyons of the Lodore . You might want to visit during late May and early June, because that is when the best flow is.
Wednesday, June 22, 2011
After seeing the glauconite and other interesting rocks, Mrs. Faatz decided she wanted to hike back up there and see what she could find. While up there for the second time, we made the discovery. Amanda saw a boulder that she wanted to test to find out what it was. Right before putting acid on it she realized that there were fossils that looked like clam and snail shells. They weren't what we thought though. These fossils were brachiopods and crinoids. Relative dating using the fossils allows us to say this rock is Mississippian in age (about 350 million years ago). These animals lived shallow tropical seas. This limestone is part of the Madison Formation and was found in the wash because it had been eroded from the cliffs above us. After the brachiopods and crinoids died, sediment slowly started to build up and eventually enough sediment was deposited over them to compress them into the boulder that we saw. Although we didn't plan on finding fossils on this trip, it was fun, interesting, and fit for a geology trip.
Monday, June 20, 2011
During the hike we were fortunate enough to view the Lodore Formation and Madison Limestone layers more closely. The Lodore Formation is a very distinct layer of rock which was formed during the Cambrian Period. It resembles pink pancakes stacked upon each other. The Madison Limestone alternated between gray and sandy red colors within the layer. (Both of these differed from the darker colored lower layer of the Uinta Mountain Group.) Large chunks of the Madison Limestone surrounded the trail and we saw sections of it where the chert hadn’t eroded as fast as the limestone. The hike was a lot of fun and when we reached the top we enjoyed a vigorous shower due to the waterfall. We all enjoyed it and the opportunity to learn more about the layers close up.
Sunday, June 19, 2011
Saturday, June 18, 2011
saw numerous fascinating geological
features. As we rafted down the river, we couldn't help but notice the cool rock walls on either side of us. The further we traveled the more layers we saw. Some layers were flat, or rather parallel to the river, while others (like the Lodore Formation shown here in the picture) are angled into the ground. Some of the layers would seem to completely disappear and show up later on down the canyon. We wondered why this happens this way. The answer is - folding and faulting during the formaio of the Uinta Moutains between 60 and 30 million years ago. When the Uinta Mountains formed a huge upfold or anticline formed. This is called the Uinta Arch
This convex fault was especially cool for us because the Green River cuts perpendicular to this huge fold. How could the river do this? It seems it should go around it. But here is the part of the story that was left out: The Uintas were eroded and covered between about 30 and 12 million years ago. The Green River established its course on this flat landscape. Then the land began to uplift again. This time it didn't fold, just slowly elevated. This uplift caused the Green River to erode downward. It was able to cut through the Uinta Arch because its course was already established across it. This is called superimposed drainage.
One of our favorite layers that we saw came near the meeting of the Yampa and Green Rivers. The rock looked like a giant steam boat. In fact, they called it Steamboat Rock. The rock looked cool, but there was in fact some geological significance to it too. It was an entrenched meander, which means there was a bend in the river that curved back around til it was very near to the place where it turned, only separated by a peninsula of land. Other than the joy of rafting, this was our favorite part of the trip. We really enjoyed all the cool geology we saw. We enjoyed watching and learning about the different layers and how they formed to create the shapes they do today. Plus, we got to go river rafting! It was one of the best trips ever!
Wednesday, June 15, 2011
By Tyrell Crane, Layne Hamblin, and Haden McAfee
What happens when you add three days, thirty miles of river, great friends, exceptional food, and some of the most breathtaking country in the world? You get a whitewater rafting trip! Boo-Ya! But not just any river trip, this river trip is classified by three things: geology that even a dummy can appreciate (trust us, we did), phenomenal memories, and food that puts even Wendy’s to shame!
By far one of the most remarkable geological marvels on this trip was Split Mountain. This was one formation that looked amazing even before you knew what you were looking at, and the story behind it is so unique it is literally world-renowned. The rock layers that compose the Uinta Mountains underwent radical changes throughout their history. Millions of years of deposition, erosion, folding, and faulting shaped the mountain into what it is today.
One of the greatest memories we all came home with occurred at the Pot Creek campsite on our first night on the river. Years of deposition from the fluxuating river levels had created a really comfortable campsite—fully equipped with a downy soft beach that served as the ideal location for beach volleyball, sand art, and turning our freshman comrade into a total sand babe. This beach was an exceptional part of the river trip.
Last, but certainly not least, was our guides contribution to the adventure. As you can imagine, managing over twenty teenage youth and their physical and emotional luggage confined to four seven foot by eighteen foot rafts can be quite a task, but despite it all, our guides consistently cranked out muy delicioso gourmet food. From boiling hot chocolate, to shore-side salads, a distended belly was a commonplace on this trip! In addition to the food, they were highly sociable and engaged themselves in our conversations. A special thanks to you Jordan (Raft Goddess), Tilt (Pancake God), Pat (Muffin God), and Ferg (Fergalicious)! You made the trip amazing!
Professor Faatz' Geology Class, Summer 2011 06/27/11