Entrenched Meanders at Dead Horse Point

Approximately 10 million years ago, the area now known as the Colorado Plateau was uplifted. It was uplifted by tectonic activity which lifted the area approximately 10 thousand feet in 10 million years. This is a significant amount of uplift in a short period of time. At that time (10 million years ago) the Colorado River was near its base level. Being near its base level, it began to meander. When the Colorado Plateau was uplifted, it caused the river to begin cutting through the underlying rock. As the river attempted to reach its base level, the land was continuously being uplifted. This caused the Colorado River to scour deep trenches into the underlying rock. As the river continued to cut down further into the rock, they became entrenched by the rock. As you can see in the picture, the Colorado River is meandering, and also notice the rock face on each side of the river hundreds of feet high. 

Formation of Arches

For arches to form, there needs to be three main criteria present.

1. first a thin wall of sandstone (as seen in picture) need

 to be present. These thin "walls" of sandstone are called fins (see fin formation on blog). These fins allow for the arch to open up all the way through the wall.

2. The next criteria that must be present is that the overlying layer of sandstone must have an underlying layer of shale. Having the less resistant rock underlying the more resistant layer causes the underlying shale to be eroded beneath the sandstone. When the underlying shale is eroded away, there is no support under the sandstone. This causes the sandstone to slowly collapse. 

3. The contact between the sandstone and the shale is the third criteria necessary for arch formation (arches form at a contact between overlying sandstone and underlying shale). The second picture shows the contact between the two layers very well along with the early stages of arch formation.

 

                          

 

This picture shows the contact between the sandstone

 and the shale very well. You can also see, in the 

center of the photo the beginning formation of an arch. 

Different Types of Arches

According to Wikapedia "The choice of "bridge" vs "arch" is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed. By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion." http://en.wikipedia.org/wiki/Natural_arch#Weather-eroded_arches
While a bridge is one form of an arch, there are actually places in the world where the arch is so big that it is an actually highway on top making it a literal bridge. Carter Caves State Park is a cave eroded arch (made of limestone that has a paved road on top of it.
There are also Coastal Arches that form in two ways, Discordant Coastlines Which form at a 90 degree angle to the water, and Concordant which form parallel to the coast line.
The ones we are all most familiar with are the Natural Arches that from in Arches National Park. There is a cool Description of how they form in this blog, but also at this link. http://en.wikipedia.org/wiki/Image:Arch_form.gif

Dead Horse Point

Dead Horse Point

By: Tania Tolbert

On the last day of our trip we stopped at Dead Horse Point. This lookout is located at the end of a thin peninsula that overlooks many neat things. We learned and observed what entrenched meanders looked like and how they formed. The river in the picture above is the Colorado River and is responsible for creating and cutting the entrenched meanders. We also were able to see the evaporation ponds of a potash mine. This mine is located in the Paradox Formation and creates potassium chloride evaporites. These evaporites are used a crop fertilizers. 

Behind me is an anticline (not very visible) and in the distance are the La Sal Mountains. 

The Fiery Furnace

The Fiery Furnace

Day #2

By: Tania Tolbert

On day #2 we went into Arches National Park to the Fiery Furnace. We went on a guided hike with Ranger Matt. While in the Fiery Furnace we were able to get up close and personal with the fins and joints. As you can see in the picture below, we hiked along parallel to the fins. We were also able to see where erosion had taken place along the joints and how it eventually resulted in the formation of fins. Ranger Matt was also very kind to show us the different arches found in the Fiery Furnace (Skull Arch, Surprise Arch, and Pothole Arch), some natural bridges and some plant (Mormon Tea and Junipers) and wildlife (toads, lizards, and ravens). We all had a great time on the hike.....even though Scott had to stay on the trail.

 Pictured above is Surprise Arch                               Nice Fins!!!!!

Flat Irons of the San Rafael

The San Rafael Swell

Flat Irons

By: Tania Tolbert

Picture taken off of I-70 heading East towards Green River

That's ME!!!!!

The San Rafael Swell is found within the Colorado Plateau and it formed about 60 million years ago due to the Laramide orogeny. During this mountain building event the crust in Utah was warped and formed multiple domes and basins. The San Rafael Swell is one of the domes that formed at that time. Over millions of years differential erosion has occurred and resulted in the formation of many unique land forms. Flat Irons are some of the most popular found on the San Rafael Swell. Flat Irons form from water eroding away at the folded rock layers. As it erodes it forms a "V" shape is created in the resistant rock layers as you can see in the picture. The part of the resistant layer that remains after the erosion process forms a flat iron. It is called a flat iron because it looks like a iron that you iron your clothes with. 

Aerial View of the San Rafael Swell

 

Cretaceous layers in Moab Utah

The Cretaceous Period (145-65 million years ago)

Through most of the Cretaceous Period, the Eastern half of Utah was covered by an ocean.In the Moab area mainly shales were deposited,  resulting in the famous, (infamous) gray, Mancos Shale. If anybody has ever been to Green River Utah, you know what I'm talking about. This area is a reflection of the conditions during this time, an ocean floor basically.
In the earlier strata layers of the Cretaceous period one can find rocks replete with dinosaur fossils.  (For a look at the dinosaurs living at this time see: http://geology.utah.gov/utahgeo/dinofossil/dinecret.htm). This layer is also know for it's uranium and vanadium deposits. In the Late Cretaceous the ocean covering Eastern Utah began to recede as the Western part of the continent started to uplift. In the Arches area, as the salt dome of today's Salt Valley Anticline started to uplift, these layers were eroded away. The Cretaceous Period was one of high temperatures, accounting for the rise of the shallow oceans. Flowering plants like the magnolia also began to thrive. For a more in depth look at the climate and more info. on the subject see: http://en.wikipedia.org/wiki/Cretaceous#Climate. The Photo above is a depiction of how the Earth looked during the middle Cretaceous Period.

Stratigraphy and Geological History---Pennsylvanian

Before this field trip the first thing we had to learn about so we could understand the rest of the geology was the stratigraphy and geological history of the parks we were going to see. Stratigraphy is a part of geology that studies the layers and layering of sedimentary rocks. For more information on what statigraphy is and how it came about check out http://en.wikipedia.org/wiki/Stratigraphy. Lets talk about the lowest layers seen in these parks. They come from the Pennsylvanian Period which is about 310 million years ago. During this time there was a restricted inland sea. This sea left layers of potash, dolomite, gypsum, salt as it went through different evaporative cycles. The salts form the Paradox Formation (see earlier blog entry about this ) .  These salts easily deform plastically which is responsible for the salt tectonism of this area.  The other formation in this period is the Honaker Trail. This formation has fossiliferous limesone, sandstone, and shale. The Honaker Trail was deposited in a shallow sea and delta.  These two formations make up the Hermosa Group. Wow that was a lot of geology and isn't amazing that we had part of the ocean in Moab, UT.  Crazy what a couple hundred million year difference makes. This is a picture of the Colorado River and it cut down to the Pennsylvanian period rock.

Upheaval Dome

Day 3 of your trip we were in Canyonland National Park. We went to Upheaval Dome. What is Upheaval Dome? Salt dome or is it a meteorite crater? One hypothesis geologists have says that it is a salt dome that was created when the salts from the Paradox Formation moved upward. The other hypothesis is a meteorite hit 60 million years ago and when it his it made a depression and then rebound flow made the dome in the middle. Erosion has long since eroded the upper part of the impact crater and its debris.  Geologists decided to try and prove which hypothesis was correct. They mapped the rocks of the entire area very carefully. While they were mapping they were looking for faults normal or thrust. If there were normal faults it would be a salt dome, but if they found thrust faults then it would be meteorite caused. They geologist found as they mapped the area that it was all thrust faults. That means that it was meteorite created. Then new proof was found. They found the presence of shocked quartz (quartz fractured in a special way) which is created by a meteorite. Answer to our question of salt dome or meteorite crater...it is a meteorite creator. Check out this site, http://en.wikipedia.org/wiki/Upheaval_Dome, for some more pictures and and a summary of what we talked about.

Soft Sediment Deformation

On day two of our trip in Moab, as we were headed to The Fiery Furnace in Arches National Park we stopped along the road and took this picture. Can you see how the smooth looking upper layer called Slickrock is dipping down into the brick- looking Dewey Bridge layer? What you are seeing is what geologists call soft sediment deformation. Soft sediment deformation is the process of the lower layers of sediments being deposited wet and the weight of the overlying layer of sediments deforming the lower layer of sediments. Isn't that neat? Now you won't look at the picture the same again!

Potash Mine:

The Potash Mine near Moab Utah is a mine where the evaporate KCl and other salts are mined. The Paradox Formation contains evaporates such as halite (NaCl), potash (KCl 0 and other salts.  The Paradox is intensely deformed due to the salt tectonism in the area. So, underground mining is impossible.   Instead they drill holes down into the ground and pump water into these holes. They then pump the water to the surface and put it in the evaporation ponds you see in the picture.    The water with the dissolved salt in it evaporates and voila! Potash.  The evaporation ponds are a really obvious feature from Dead Horst Point.