Final Project Phy103
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7-2 Final Project Milestone: Geologic Analysis.
PHY-103 Earth System Science
Southern New Hampshire University
2
I.
Executive Summary
This report will detail the geology, climate, and landscape findings regarding the proposed
subdivision in the area of Walterville, Oregon. The area of the proposed subdivision is in an area
with many features. These include geologic features, possible tectonic activity, volcanic activity,
flooding, and heavy precipitation.
First, I will detail the geologic features in the area, including soil stratigraphy and soil
profiles. This information will help to decide where would be the best location for the
subdivision. The topographical features in the project area have the potential to cause flooding
and erosion in the proposed subdivision. This report will detail the creation of these features and
how they will affect the project area. There is evidence of tectonic activity within the project
area, which may cause concerns in the future. Finally, I will discuss the climate and weather in
the area. The project site is located in an area prone to heavy precipitation, which can cause
flooding. This information must be considered when deciding where the subdivision should be
placed in the project area.
II.
Geology
The rock types present in the project areas stratigraphy and cross-section in order from the
surface down are limestone (A), sandstone (B), granite (I), limestone (C), coal (D), siltstone (E),
coal (F), sandstone (G), and schist (H) (Bergmann, 2011). The first layer, limestone, is a
biochemical sedimentary rock and is mostly comprised of calcite (C
a
CO
3
) (King n.d-a.).
Sandstone is a clastic sedimentary rock and is made up of mainly quartz and clay (GeoKansas,
n.d.). Granite is an intrusive igneous rock, meaning that it is formed deep within the earth from
3
cooled magma rock (Lutgens et al., n.d). Like limestone, coal is also a sedimentary rock. Unlike
limestone, it is an organic sedimentary rock made up of once-living organisms that have been
compressed rock (Lutgens et al., n.d). Schist is the last of the rock types that are present within
the project area. Schist is a foliated metamorphic rock that has shale as a parent rock (King, n.d-
b.).
Sediment is usually deposited in layers, with the bottom layers being the oldest and the top
layers being the youngest. There are exceptions to this rule in the form of dikes and sills. Dikes
are incongruous areas that form in the rock layers from magma that is forced upwards through
the sediment layers (Lutgens et al., n.d). Sills are horizontal areas, the result of magma that finds
weak spots in rock structures (Lutgens et al., n.d). The oldest sediment layer is schist. The schist
layer is at the bottom of the stratigraphy, located underneath the other layers. Even though
granite is underneath the schist, it is a younger rock due to its presence throughout the layers and
into the sandstone layer B (Bergmann, 2011). The next oldest layer is sandstone, then coal,
siltstone, coal again, limestone, and sandstone, as they are located above the bottom layer. Layer
A is limestone and the youngest layer due to its location at the top of the other layers (Bergmann,
2011).
Limestone is usually formed in warm, shallow saltwater but can be formed in lakes and hot
springs as well (Basics-Depositional Environments, n.d.). Sandstone generally forms in basins
both near and far from water after minerals are washed down and compacted over time
(GeoKansas, n.d.). Limestone and sandstone are layered together in the stratigraphy, meaning
that they were formed in or around water. Siltstone is found near rivers and streams that weave
through floodplains. Schists are formed when shales and sandstones are subjected to heat and
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compression (King, n.d-b.) Coal is found in areas that are damp and abundant in plant debris
(Lutgens et al., n.d).
The included soil profiles give insight into the potential for erosion (
Final Project Soil
Profiles
, n.d). Soil profile A has four horizons. The first horizon, O, is made up of organic matter.
Horizon A is next and is made up of topsoil, B is subsoil, and C is the substratum, which is
weathered or poorly weathered rock (
Soil Horizons - Soil Ecology Wiki
, n.d.). Horizon O is not
always present in soil profiles. The occurrence of this horizon means that at some point, organic
matter covered the topsoil. Soil profiles B and C do not have an O horizon. This could be due to
glacial movement or changes in the boundaries of streams and rivers (
how parent material
affects soil profile development
, n.d). The project area is in the Cascade Range. Soil and
sediment have been moved from higher in the Cascades down to the project area, causing
different profiles (
How parent material affects soil profile development,
n.d). The topological
map of the project area shows many streams and rivers, creating the possibility of flooding. The
stratigraphy shows two layers of limestone, which indicates that the area has flooded before
(Basics-Depositional Environments, n.d.). In years with high precipitation, the likelihood of
flooding increases exponentially.
The project area is located within an area with a known thrust fault as well as a volcano. The
thrust fault is visible on the site stratigraphy and cross-section as well as on the topographical
map (
Final Project Stratigraphy and Cross Section,
n.d). Thrust faults are found in subduction
zones, meaning areas where the lithosphere (crust and upper mantle) is sinking back into the
mantle. Earthquakes at thrust faults occur due to severe compressional stress (Lutgens et al., n.d).
The presence of a fault in the project area opens the possibility of earthquakes. These
earthquakes may be small, but there is a chance for a larger earthquake to happen. There is a
5
volcano in the vicinity as well (
Final Project Walterville Topographical Map
, n.d-d). While it is
unlikely that the volcano itself will erupt, it is possible that an earthquake could cause magma to
be forced to the surface, causing fires or destruction of the subdivision. The project is also in a
floodplain, surrounded by rivers and streams. This can bring the possibility of flooding.
III.
Streams and Tectonics
There are multiple topographical features seen on the map of Walterville (
Final Project
Walterville Topographical Map
, n.d-d.). These features are all related to the stream processes that
have occurred in the region and include drainage basins, divides, stream channels, valleys,
floodplains, and oxbow lakes (Lutgens et al., 2021). Drainage basins, also known as watersheds,
are formed when surface water from precipitation is moved downward into low-lying areas
(Lutgens et al., 2021). Drainage basins are bounded by imaginary lines called divides. In some
instances, a divide can be seen as a ridge above a drainage basin. In other instances, the divide
may be harder to see due to smoother topography (Lutgens et al., 2021). The water that collects
at the bottom of drainage basins joins with other bodies of water to create streams and rivers.
Drainage basins are seen in multiple areas of the project site topographical map (
Final Project
Walterville Topographical Map
, n.d-c
)
, the most relevant being where the proposed project site is
located. Streams either create alluvial channels or bedrock channels depending on the type of
material the stream is flowing through (Lutgens et al., 2021). Alluvial channels are created when
streams flow through loose sediment. These channels are capable of changing considerably, as it
is easier for the stream to erode, move, and deposit sediment. Oxbow lakes are formed when an
alluvial channel meanders over time and eventually encounters hard material, causing erosion to
slow (Lutgens et al., 2021). An oxbow lake is seen on the Walterville topographical map, just
south of Camp Creek Road (
Final Project Walterville Topographical Map,
n.d-c). This causes
6
the upstream meanders to catch up with the downstream meanders. As this occurs, the land that
is between the meanders erodes until a portion of the river is cut off (Lutgens et al., 2021).
Bedrock channels are formed when a stream or river flows through solid rock, transporting
coarse sediment. As channels flow through the landscape, they create valleys through erosion
(Lutgens et al., 2021). Depending on the age of a river, valleys are either U-shaped or V-shaped.
Younger rivers are found in V-shaped valleys like the one on the topographical map near Mount
Washington (Lutgens et al., 2021). V-shaped valleys are created from the channel downcutting as
it moves toward base level. Older rivers are found in U-shaped valleys. U-shaped valleys are
formed when a river or stream can no longer downcut. Once the channel reaches base level, it
starts to erode the valley walls, making the valley wider until it creates a floodplain (Lutgens et
al., 2021). Floodplains are areas that are flooded when a river overflows during a flood.
Floodplains are seen in proximity to the proposed project site (Lutgens et al., 2021).
The proposed project site is situated in an area at risk of flooding, mudslides, and erosion.
The development is in a mountainous area with a history of heavy precipitation and overflow
from streams (Southern New Hampshire University, n.d.-a). It is extremely likely that the homes
within project sites A and B will be subject to flooding during times of high precipitation. When
looking at historical data, six out of the top ten record rainfall events have occurred in the last 20
years (Southern New Hampshire University, n.d.-b). Erosion is likely to occur due to the amount
of water moving through the area. As the stream located near site A starts to meander, it is likely
to erode the land underneath any homes in the area. Site C is located near the edge of a drainage
basin, which will cause that site to be prone to mudslides and rockslides during periods of heavy
rain both in the area and at higher elevations (Southern New Hampshire University, n.d.-a).
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The proposed project site is near a fault line and a dormant volcano, Mount Jefferson. This
indicates the potential for tectonic activity. Faults are fissures in the earth’s crust that allow
blocks of rock to slide past one another to relieve built-up pressure (Lutgens et al., 2021). The
fault seen on the topographical map looks to be a convergent plate boundary (
Final Project
Walterville Topographical Map,
n.d-c). Convergent plate boundaries are areas where two
tectonic plates move toward each other, causing one plate to be forced under the other. The area
where two convergent plates meet is also called a subduction zone due to the sinking
(subducting) of one plate into the earth's mantle (Lutgens et al., 2021). The Cascade Range,
where the project site is located, was formed from the Juan de Fuca plate subducting under the
North American plate (
Mount Jefferson | U.S. Geological Survey
, n.d.).
Earthquakes occur on average every 70-90 years (
Final Project Historical Data,
n.d-c).
Earthquakes in the area average a magnitude of 6.8. According to the historical data, the last
earthquake along the fault occurred 85 years ago and had a magnitude of 6.9, meaning that it is
probable that another earthquake will occur in the next 5-10 years, causing heavy damage in the
area (
Final Project Historical Data,
n.d-c). Site C is in a very vulnerable area if an earthquake
occurs due to its proximity to the mountains. The buildings in the project area are likely to be
damaged by landslides and debris falling from the mountains. Sites A, B, and C are likely to have
damage from an earthquake due to their proximity to the various creeks and waterways in the
area. The ground near the water is likely saturated, causing the ground to move in a fluid-like
motion called liquefaction (Lutgens et al., 2021).
The volcano in the vicinity, Mount Jefferson, is a stratovolcano located in the Cascade
Range. (NASA Earth Observatory, n.d.). It is composed of andesite and dacite (
Mount Jefferson |
U.S. Geological Survey
, n.d.).
8
If Mount Jefferson were to erupt, it could cause devasting consequences. Lava is likely to flow
through river valleys toward the project site, and ash and pyroclastic materials will reach areas
hundreds of miles away (
Mount Jefferson | U.S. Geological Survey
, n.d.). Mount Jefferson has a
history of small eruptions every 600-700 years. The last small eruption occurred roughly 630
years ago (
Final Project Historical Data,
n.d-c). The last major eruption occurred approximately
15,000 years ago (NASA Earth Observatory, n.d.). Since Mount Jefferson erupts every 600-700
years, a small eruption may occur in the next 50 years. If an eruption does occur, the project site
will be vulnerable to falling ash, pyroclastic materials, and lava flows (
Mount Jefferson | U.S.
Geological Survey
, n.d.).
IV.
Weather Analysis
The Walterville project site has an annual average temperature of 51°F and an annual
precipitation rate of approximately 2.78”. July and August are the months with the highest
temperatures and average 68°F. November and December both have the highest precipitation
rates, averaging 5.7” inches a month (
Final Project Walterville Climograph,
n.d-e.). The
temperatures and precipitation in the area are indicative of a polar front. Polar fronts are located
over jet streams that are positioned between the 50° and 60° latitudes in the northern and
southern hemispheres (
The Jet Stream
, n.d.). The polar front is an area that separates polar air
from subtropical air (Lutgens et al., 2021). The collision of warm and cool air can cause mid-
latitude cyclones to develop, which causes unstable weather patterns with heavy precipitation
(Lutgens et al., 2021).
The project area will see intense storms due to its location within the polar front. In the
winter months, precipitation will be heavy, with November having the majority of record
9
precipitation events (
Final Project Historical Data,
n.d-c). Heavy rainstorms occur in the winter
months due to the convergence of cold fronts with warm subtropical air. The spring months
receive moderate rainfall. Snowstorms, rainstorms, and thunderstorms are all possible in the
region (Lutgens et al., 2021). High winds, hail, heavy precipitation, and even a tornado is
possible due to the presence of the polar front (Lutgens et al., 2021). The summer months are the
driest, with minimal precipitation and higher temperatures.
On November 02
nd
, 1917, the region received 12.09 inches of rain, and 10.02 inches fell on
November 16
th
, 1966. When looking at the historical data, I can calculate that there are events
with excessive rainfall about every ten years by using the recurrence interval calculation (
Final
Project Historical Data,
n.d-c). The recurrence interval is the probability that an event will occur
within a certain period (Young, n.d.). By using the recurrence interval formula of the number of
years in the record (N) divided by the number of events (n) (Baer, 2021.), I calculated that there
were ten extreme rainfall events within a 96-year period. By dividing the ten events by the 96
years of data, I am able to calculate that extreme rainfall occurs approximately every 9.6 years
(
Final Project Historical Data
, n.d-c).
Within the project area, it is likely that extreme precipitation events will occur, leading to the
flooding of creeks and streams in the area. Erosion is another factor that needs to be addressed.
With the high amounts of precipitation and the fact that the project site is within the vicinity of
multiple drainage basins and within a floodplain, there are likely to be areas of heavy erosion
along streambanks and under buildings. There are mountains near the project site that are likely
to have landslides occur during heavy precipitation events as well (
Final Project Walterville
Topographical Map
, n.d-d.). These extreme events happen with enough frequency, along with
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high amounts of annual precipitation, that it will be difficult to repair any damage caused by
flooding and erosion.
V.
Analysis of Findings
Due to the findings of this report, I would advise not to build within the project area. The
project area is prone to flooding, landslides, and erosion, and there is a likelihood of volcanic
activity or earthquakes. The historical data shows that heavy precipitation events happen
approximately every ten years, which will severely impact any homes that may be built in the
project area. I advise against building in this area and suggest finding a more suitable area for a
subdivision.
11
References
Baer, E. M., (February 09th, 2021), Teaching Recurrence Intervals, Carlton.edu,
https://serc.carleton.edu/quantskills/methods/quantlit/RInt.html
Basics--Depositional environments
. (n.d.).
https://commons.wvc.edu/rdawes/g101ocl/basics/depoenvirons.html#:~:text=A
%20depositional%20environment%20is%20a,are%20sometimes%20called
%20sedimentary%20environments.
Bergmann, J. (2011, February 6).
How to read a geologic map (3/3)
[Video]. YouTube.
https://www.youtube.com/watch?v=5EZbHCxv0NY
King, H. M. (n.d.-a).
Limestone: Rock uses, formation, composition, pictures
.
https://geology.com/rocks/limestone.shtml
King, H. M. (n.d.-b).
Schist: Metamorphic Rock - Pictures, definition & more
.
https://geology.com/rocks/schist.shtml
Lutgens, F. K., Tarbuck, E. J., & Tasa, D. G. (2021). Foundations of Earth Science (9th ed.).
Pearson Education (U.S.).
https://bookshelf.vitalsource.com/books/9780135851609
Mount Jefferson | U.S. Geological Survey
. (n.d.).
https://www.usgs.gov/volcanoes/mount-
jefferson
NASA Earth Observatory. (n.d.).
Mount Jefferson
.
https://earthobservatory.nasa.gov/images/82396/mount-
jefferson#:~:text=Mount
%20Jefferson%20is%20a%20stratovolcano,including%20lava%20flows%20and
%20lahars.
Sandstone | GeoKansas
. (n.d.).
https://geokansas.ku.edu/sandstone
12
3.6 - How Parent Material Affects Soil Profile Development | Soil Genesis and Development,
Lesson 3 - Soil Forming Factors - passel
. (n.d.).
https://passel2.unl.edu/view/lesson/2b7d02fa1538/6
Soil Horizons - Soil Ecology Wiki
. (n.d.).
https://soil.evs.buffalo.edu/index.php/Soil_Horizons
Southern New Hampshire University. (n.d.-a). 1-2 Final Project Milestone One: Geologic
Analysis.
Final Project Soil Profiles
.
Southern New Hampshire University. (n.d.-b). 1-2 Final Project Milestone One: Geologic
Analysis.
Final Project Stratigraphy and Cross Section
.
Southern New Hampshire University. (n.d.-c). 4-2 Final Project Milestone Two: Streams and
Tectonics Analysis.
Final Project Historical Data
.
Southern New Hampshire University. (n.d.-d). 4-2 Final Project Milestone Two: Streams and
Tectonic Analysis.
Final Project Walterville Topographical Map
.
Southern New Hampshire University. (n.d-e.). 6-2 Final Project Milestone Three: Weather
Analysis.
Final Project Walterville Climograph
.
The jet stream
. (n.d.). National Oceanic and Atmospheric Administration.
https://www.noaa.gov/jetstream/global/jet-stream
Young, J. B. R. W. F. H. a. W. S. (n.d.).
FS-036-98: What is a Recurrence Interval?
https://pubs.usgs.gov/fs/FS-036-98/text/what.html
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