Download Wasatch Range and the Farrallon Plate Jeannie Miller Directions to

Wasatch Range and the Farrallon Plate Jeannie Miller
Directions to Big Cottonwood Canyon
6200 S. turn right onto Wasatch Blvd. Turn left onto Big Cottonwood Canyon Rd. at 7200 S.
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Wasatch Range and the Farrallon Plate Jeannie Miller
Wasatch Range and the Farrallon Plate
Jeannie Miller
Geology
Teacher: Robert Armstrong
December 10, 2014
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Wasatch Range and the Farrallon Plate Jeannie Miller
Wasatch Range and the Farrallon Plate.
On a clear day, anywhere from the Salt Lake Basin one can turn and look east and see the
majestic Rocky Mountains. Majestic as they are, they are relatively new compared to other mountain
ranges found throughout the world. These mountains are unique in their creation. Most mountain ranges
are created by subduction; the Rocky Mountains are no different. The difference comes in the subduction
zone lying off the coast of southern California. The Farrallon Plate began to subduct about 85 million
years ago under the west coast of California. Instead of dropping into the asthenosphere, where it would
have melted, the Farallon Plate rode directly under the Continental Lithosphere eastward, pushing the thin
continental crusts upward and crumpling them, in some cases pushing basement rocks that had been
buried since the Precambrian times, upward. (Armstrong, 2014). Because of this, we have in our Rocky
Mountains, a mixture of ancient and recent rocks, slabs that project upward, while others are tilted at
angles. These mountains are a mixture of granite, quartzite, and of course, sedimentary rock, for the
newest of formations of mountains. We also find where sediment has been worn away at the top of the
mountains, igneous rock.
Donald Forsyth, a geophysicist of Brown University, agrees with the fact that the Farrallon plate
subducted under the North American and Pacific plate. Yun Wang, a former Brown University graduate,
and Forsyth came to this conclusion from their physical research, that the plate broke off fairly deep,
leaving large parts of the plate to rise again to the surface. In researching the Baha, California area where
the subduction is believed to have gone under, they found parts of andesite deposits along Baha and
central California coastline. Andesite deposits are volcanic in nature and come from the Oceanic crust
material, thus, they used this information to substantiate their theory. ( Forsyth and Yun Wang 2013).
As the Oceanic crust subducted under the North American and Pacific Plates, it rode directly
under the lithosphere, eastward, crumpling the surface, constructing the Sierra Nevada's and the Rocky
Mountains. Now that the Farrallon Plates have pushed this far inland, acting like a spring of coils, it is
moving westward again. As it moves westward, it is putting stress on the faults that exist along the
Wasatch Front. (Armstrong, 2014).
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Wasatch Range and the Farrallon Plate Jeannie Miller
The Wasatch Fault
Earthquakes are movements along a fault. There are three different types of faults; normal, strike-slip, it
will slide past a rock headed in the opposite direction, and reverse. If the fault is always moving, it helps
to release some of the tension, instead of having a huge build-up of tension, no matter what type of fault it
is.
In the Wasatch Range area, we find the result of two of these types of faults. The North American Plate
has been pulled apart into blocks. The blocks have been tilted in the shape of slanted mountains. Reverse
faults have compressional forces; two plates pushing toward each other. So again, you have blocks that
will move upward as another move downward, creating a slanting look.
As the Farrallon Plates are now starting to move westward, the compressional effect from convergence is
now springing back and the effect is of a divergent-plate, causing crustal extensions and serious
earthquakes.
The effects from any of these earthquakes can be detrimental to those who live along the Wasatch Front.
Most of the people in the Salt Lake Valley live on what use to be Lake Bonneville. This lake bed, still
containing much ground water from the still existing Salt Lake, poses a serious threat. In an earthquake
on this lake bed, you would experience high liquefaction. (Christianson, G.E., 2006). People who live
east of 9th East have their homes built on granite. However, those who have their homes built west of 9th
East, much of the homes are built on this lake bed. When the divergent-plate slips like a spring, it will
cause earthquakes high on the Richter scale.
Earthquakes; measuring them.
A seismograph detects arrival times and records the waves caused by earthquakes. To record the motion
on the graph, the waves are amplified. The amplitude of the earthquake is the distance between the crest
and trough or arrival time of the P- and S- waves.
Intensity of an earthquake.
Mercalli Scale was a way to measure the intensity of an earthquake. It has real measurements of the effect
on people…if the books in the house fell off the shelves it was a lower measurement as compared to if the
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Wasatch Range and the Farrallon Plate Jeannie Miller
house shifted off its foundation, this would be a higher intensity earthquake. The Mercalli Scale was very
practical and user friendly. Anyone anywhere could use the Mercalli Scale. Another type of measuring an
earthquake is the Richter Scale, spoken of earlier. It uses logarithmic calculations to measure the
amplitude of an earthquake; the higher the waves, the higher the amplitude of the earthquake. The damage
is also greater. Damages produced by earthquakes are measured in two ways, primary and secondary.
Primary damages are the most lasting and permanent. Man-made structures are totaled. A secondary
damage might be a fire brought on by the earthquake.
Nature is always in motion, tearing down and building up from earthquakes to subductions, from
volcanoes to landslides; the Cottonwood Canyons are good examples of it.
We can see water getting into rocks, then freezing, cracking boulders that may weigh tons, breaking the
boulders into smaller and smaller pieces over time and then carrying those pieces downstream to be
buried under more and more pressure, until thousands of years later, it is reformed into a new rock, or
even carried out to the ocean and subducted into the athenosphere and recreated into some other kind of
rock.
Trees can grow from the smallest amount of dirt that has gotten into a cavity of a rock. As the tree
grows, so do the roots. The roots help to split the rocks as frozen water would help split it. Thus, nature is
always in motion, breaking down and building up.
Man plays a part in the evolving of nature. The canyons are used for recreational activities by the
thousands that live just in the valleys below. When man is aware and takes care, nature continues her
recycling process. But, when man over burdens her with pollutants, such as mining sludge and
contaminates, it affects the whole eco-system. It can take thousands of years to reclaim the land that has
been poisoned by so few.
Carbon monoxide has a detrimental effect on the Canyons; so many of the trees are dying that are
close to the side of the road. The trees cannot handle the carbon monoxide given off as waste from the
thousands of vehicles that traverse the canyons every day.
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Wasatch Range and the Farrallon Plate Jeannie Miller
Hope and Change for the Future.
We are starting to see a change in man as he takes care of the environment. Cars are being created
that will run off of electricity, using only a minimal amount of carbon fuel to regenerate, then it switches
back to being electric. We are seeing alternative forms of electric transportation. But, this is not enough.
We need to harness energy from the sun and wind power.
Nature cannot recyle by herself when so many contaminate. We need to leave no trace as we
enjoy nature. (Uinta- Wasatch- Cache National Forest. Leave No Trace Pamphlet, 2013). As we become
more aware of nature and her needs, more will be involved in living in our eco-system instead of
destroying it. We also need to be more aware of the changes in nature so that we can adapt. Earthquakes
are part of the earth’s movement. We need to build homes and our systems that work with nature to
survive.
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Wasatch Range and the Farrallon Plate Jeannie Miller
References:
Armstrong, R. (2014). Geology adjunct teacher at Salt Lake Community College.
Stacey, K. (2013). Under California: An ancient tectionic plate. Published in: Proceedings of the National
Academy of Sciences.
Uintah- Wasatch- Cashe National Forest pamplet; Leave no trace (2013).
Utah Geological Survey; General Hazards: Christenson, G.E., and Ashland, F.X., Compiler, 2007. A plan to
reduce losses from geological hazards in Utah-recommendations from the Governor’s Geological
Hazards Working Group 2006-2007. Utah Geological Survey Circular.
USGS Map and a hand drawn map using the USGS Map as a guide.
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Wasatch Range and the Farrallon Plate Jeannie Miller
Up the Big Cottonwood Canyon.
.
Up the Little Cottonwood Canyon.
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Wasatch Range and the Farrallon Plate Jeannie Miller
The rounding of rocks is from the
water; the squared rocks have
recently fallen off the mountain
or have been placed by someone
in the park.
Many mountains were carved by glaciers millions of years ago.
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Wasatch Range and the Farrallon Plate Jeannie Miller
The sorting of rocks, gravel, pebbles, and silt will take place as snow turns into running water.
The weatherizing of rocks on the mountain.
Water gets into the cracks then freezes. This expansion causes the rocks to break away from the
mountain. This is just part of the process that turns rocks into sediment.
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Wasatch Range and the Farrallon Plate Jeannie Miller
U.S. Geological Survey and a
hand drawn map of the
Big Cottonwood Canyon.
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Wasatch Range and the Farrallon Plate Jeannie Miller
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