Weathering and Erosion in the Bitterroot Mountains and my Basement
Taylor J. Hellman
Senior
Biology Education
Earth Science
February 2, 2015
1. The location and the object of weathering
For my example of weathering and erosion I chose two photos of the Bitterroot Mountains in
Western Montana. Over fall break I was able to hike in these beautiful mountains on the
Blodgett Trail.
Photo #1
Photo #2
2. Weathering and Erosion Processes
Weathering is the breakdown of rock, soil, or minerals from mechanical/physical processes or by
chemical processes. Mechanical weathering can be described as physical weathering that is done
by either water, heat, ice, or pressure. These physical factors can cause the destruction of rockmade structures. Weathering is the degradation of rock-made structures through time from the
outside environment over time. Mechanical weathering does not change the physical
composition of the rock, but it just changes its physical state. Chemical weathering is the
weathering of rock from direct effect from atmospheric chemicals or biologically produced
chemicals. Chemical weathering can be seen more in climates that are hot and wet, but chemical
weathering takes place everywhere. Chemical weathering does change the physical composition
of the rock. Also, mechanical weathering and chemical weathering work hand-in-hand. They
can help speed up the processes of each other. Mechanical weathering can break down rocks
into smaller pieces with greater surface area, and this can allow chemical weathering to be more
effective in weathering that material. Erosion is the movement of rock, soil, or sediment from
one location to another. Erosion is often confused with weathering, but the main difference is
that erosion is the removal of sediment or rock to another location while weathering is just the
breaking down of rock. Erosion can be accomplished by wind, water, or ice such as glaciers.
These erosion processes have helped sculpt many of our nation’s landmarks, and it is the reason
why most of our mountain ranges occur in the world.
3. The type of weathering and erosion processes operating at this site
Weathering is visible in both photos that were presented previously. The Bitterroot Mountains
are at a high elevation, so the weathering agents that predominantly effect this area are sheeting
and frost wedging. Deep cracks and gouges in the rock (seen in both photos) of this mountain
range are caused by frost wedging. Sheeting can be seen in the second photo as the removal of
overburden reduces the pressure on the rock that is slowly exposed.
Erosion in the Bitterroot Mountains was caused by the glaciers moving across America during
the last ice age. Precipitation or the addition of running water also contribute to erosion of the
mountains. Mass wasting can been seen in the first photo. In the valley of the mountains there
were smaller rocks, boulders, and signs of sediment flow from mass wasting. Gravity and the
angle of the slope of the mountain are important aspects of the mass wasting of this mountain
range. Wind is another environmental factor that could have caused the movement of small rock
particles as well.
4. How active/advanced is the weathering process?
The Bitterroot Mountains are a relatively old mountain range. It is made mostly of granitic rock,
but sedimentary rock can be found in the valleys or areas of lower elevation. The mechanical
weathering processes such as sheeting and frost wedging can be seen in both photos. Cracks and
broken surfaces of rock can been seen in both photos, and they are examples of how active frost
wedging can effect a mountain area. Biological factors and activities also effect the mountains
as there are caves and animal burrows in the area. Also, human activity contributes to the
weathering of the Bitterroot Mountains because of the formation of trails and hiking paths. I
consider these mountains to be aging at a relatively average rate compared to most mountains in
the United States.
5. How active/advanced is the erosion process?
The U-shaped valley (seen in picture #1) show the erosional action from the glaciers during the
last ice age. The moving glacier caused the valleys and gouges that are associated with this
mountain range. The movement of the glacier cause the smoothing out of the valleys, and it
caused weathered material to be moved to other areas. It also helped create the jagged look of
these mountains. Mass wasting is also confirmed by these photos because there were smaller
rocks and boulders at the bottom of the valleys. Rock slides or snow avalanches are active mass
wasting elements that continue to contribute to the erosion of these mountains.
6. What is the likely outcome of the above mentioned weathering and erosional processes?
The weathering processes active in these mountains are likely to continue as they have because I
do not see the climate changing in this area. Larger rock structures in this area will continue to
disintegrate from the weathering processes of sheeting and frost wedging. Once smaller rock
particles are formed the erosion in this area will continue to move sediments and smaller rocks to
the valleys and down the mountain. The mountains will eventually become low hills covered by
soil from sediments, but this process will take millions of years. The rock cycle will continue its
course as magma and plate activity will cause the formation of new rock and mountain ranges.
7. The location and the object of weathering due to human activity.
My example of weathering and erosion from human activity is a photo of when we had to put a
sump pump in our basement during the summer of 2011.
8. Weathering and Erosion Processes
The weathering that took place in this photo was from human activity, and it was mechanical
weathering. We used a jack hammer and a sledge hammer to break the concrete into smaller
rock particles. We also used wedges to help pry the concrete out from the ground. The erosional
processes that took place we a result from our hard work. We carried out concrete and four feet
of dirt from the hole in buckets in order to make an adequate sump pump area. Both the
weathering and the erosional processes were from human activity/intervention, but it was
necessary in order to solve our house’s ground water problem.