Hogbacks

San Rafael Swell and Hogbacks

On the Field Studies Fall 2011 class we went to explore the geology of the San Rafael Swell in Eastern Utah. The "swell" in this geological feature refers to dome which is pictured on the right- and on the San Rafael the west side of the dome  is at a gentler slope then the eastern side. As you drive through it you pass through a lot of time, because the closer to the center of the dome you get the older the layers get - it's like traveling through time in just a few short hours!

My favorite part about the trip was seeing the hogbacks on the eastern side of the dome. Many people believe that this geological formation is from the rock layers being pushed violently into the air from forces below (like earthquakes or the like) but those who know and understand more about geology understand that hogbacks don't have such a violent and sudden past.

Rather, this is from the dome itself and it's steeper eastern side.

As shown well in the picture to the left, you can see the angle of the rocks as they slop away from the anticline. These layers, like any other exposed formation, are then subjected to weathering. This lead to softer

shape, which leads to spectacular looking triangles that we call "flat irons". layers being eroded away and the more resist layers (like sandstone, etc) sticking around a little longer. As they erode away, little streams and rivers cut them into an ^ shape.

These are one of my favorite things in geology, I think they look so impressive and striking. And then knowing just how they were formed makes them even cooler - who needs dramatic and tragic earthquakes to make these things with you have geology to back you up?

~Tauni Sutherland

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:

Beaches.

Beaches along the sides of rivers are formed by deposition of sand by the river during periods of high discharge. Discharge is amount of water flowing through a river a given point of time. Discharge is measured in cubic feet per second or "cfs" and is calculated by multiplying the width(in ft) x depth (in ft) x velocity (in ft/sec) . Discharge of a river increases during periods of snow melt and periods of heavy or prolonged rainfall. During periods of high discharge the height of the river increases. If the river is in a deep canyon like the Green River in the canyon of the Lodore, it doesn’t tend to get much wider. It just gets deeper and flows faster. This faster flow allows the river to scour (pick up) the sediment from the bottom. Also, when the river is flowing faster it can pick up and transport larger sediment like sand.

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.



Tanner Agren

Summer Geology Field Studies - Green River/Lodore Canyon

The June blogs were composed by students in the Snow College Geology Field Studies class summer of 2011. Our class studied the fascinating geology of the Green River through Dinosaur National Monument. Holiday River Expeditions made this possible with their educational discounts. The Green crosses the Uinta Arch, Mitten Park Fault and last, but not least Split Mountain Anticline. The area was made famous by John Wesley Powell in his account of his 1869 expedition: "Exploration of the Colorado River and its Canyons". Wallace Stegner said "Nearly everyone who runs any part of the canyons now .. either carries this story of Powell's in his duffelbag or has it read or recited to him around the fire while the tamed Colorado slips past." Lodore Canyon was the first real white water the expedition encountered. It was a dream for me to experience rapids that Powell's expedition named like Hell's Half Mile and Disaster Falls and the famous Canyon of the Lodore, Echo Park, Rainbow Park, Island Park and Split Mountain. I hope my students appreciated how cool it was to be there. The icing on the cake: flows that haven't been seen since 1984. Fast, big water, great guides and a great river company. Thanks to Karen, Pat, Jordan, Ferg and Tilt from Holiday. Thanks to UB Summer Component for their support. I hope my student blogs will help you to understand the geology of the river and the experience through their eyes.

Renee Faatz June 2011

Geology of the Green River

Geology blog
6-29-11
Layne Hamblin

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.

by:layne hamblin

Rapids By: Sarah and Kaylee

There are basically two different parts of the river. The rapids and the smooth lazy part; depending on what you're in the mood for, you are sure to have a good time! Everyone has heard of rapids, but what exactly is a rapid? There are four factors which either separately or in combination can create rapids: gradient, constriction, obstruction, and flow rate. Constriction happens when water flow in a river is forced into a narrower channel, the pressure causes the water to flow faster creating rapids.Obstruction is when there is a rock or steep drop in the river bed, then "obstructing" the flow of water. Rapids are a geological phenomenon that occurs when there is a fast moving body of water that is littered with rocks. Since water erodes soft land faster, these hard rocks remain where they are, making incomplete barriers. The rushing water moves around the rocks and often foams into white water. Rapids are also at points of the river where there is a relatively steep gradient, making an increased water flow and turbulence. A rapid forms due to shallowing of the river characterized by rocks exposed above the water surface. We saw most of the rapids when we were in the Lodore and Split Mountain Canyons because that was where the gradient was the highest.
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.

Sources:http://en.wikipedia.com.org/wiki/whitewaterhttp://www.diffen.com/difference/rapid-vs-waterfall

Unexpected Findings

In geology class we went on a required river rafting trip which lasted three days and two nights. At night we set up camp on a beach or sandbar. After setting camp for the second night, we decided to take a hike up a wash near our camp. We found lots of wild flowers and a variety of rocks, some with crystals, others brown and bland, but mostly chert and limestone. While hunting for interesting rocks, the advisor that was with us found a rock that we later found out contained a mineral called glauconite. Mrs. Faatz was very excited to see this and told us that this rock is glauconitic sandstone from the Lodore Formation. Glauconite is a clay that forms in shallow marine conditions. It is "typically found as rounded aggregates or 'pellets' of very fine grained scaly particles, having a blue-green to yellow-green color" (http://www.mindat.org/)

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.