There are two rocks that have rolled down the mountain and
landed close to the Bonneville Shoreline Trail. These rocks are
located at : N 40 11.080 W 111 36.027 (The North Rock) and N 40
10.822 W 111 35.731 (The South Rock).
The North
Rock
One day I was running along the BST (Bonneville Shoreline Trail)
and noticed that someone had been digging up these big holes and I
wondered why someone would do that. I ran by these holes all summer
long. Then one day on returning home from a run, I noticed the
pattern of the holes and that they led up the mountain. Then I
looked at the rock (the North rock) and realized that it had rolled
down the mountain and made these holes or impact craters. (Boy, did
I feel dumb for 1) not noticing this rock that wasn’t there the day
before, and 2) not realizing what had happened.) Later on I found
out that another rock (the South rock) had come down about the same
timeframe. Here are some things to learn about erosion and why
rocks come down the mountain.
Dictionary:
erosion (i-ro'zh?n)
n.
- The process of eroding or the condition of being eroded:
erosion of the beach; progressive erosion of confidence in our
legal system; erosion of the value of the dollar abroad.
- The group of natural processes, including weathering,
dissolution, abrasion, corrosion, and transportation, by which
material is worn away from the earth's surface.
Erosion is a broadly defined group of processes involving the
movement of soil and rock. This movement is often the result of
flowing agents, whether wind, water, or ice, which sometimes
behaves like a fluid in the large mass of a glacier. Gravitational
pull may also influence erosion. Thus, erosion, as a concept in the
earth sciences, overlaps with mass wasting or mass movement, the
transfer of earth material down slopes as a result of gravitational
force. Even more closely related to erosion is weathering, the
breakdown of rocks and minerals at or near the surface of Earth
owing to physical, chemical, or biological processes.
The first step in the process of erosion is weathering.
Weathering, as the term is used in the geologic sciences, refers
physical and chemical changes in rocks and minerals at or near the
surface of Earth. A mineral is a substance that occurs naturally
and is usually inorganic, meaning that it contains carbon in a form
other than that of an oxide or a carbonate, neither of which is
considered organic. It typically has a crystalline structure, or
one in which the constituent parts have a simple and definite
geometric arrangement repeated in all directions. Rocks are simply
aggregates or combinations of minerals or organic material or
both.
There are three kinds of weathering: physical or mechanical,
chemical, and biological. Physical or mechanical weathering takes
place as a result of such factors as gravity, friction,
temperature, and moisture. Gravity may cause a rock to drop from a
height, such that it falls to the ground and breaks into pieces,
while the friction of wind-borne sand may wear down a rock surface.
Changes in temperature and moisture cause expansion and contraction
of materials, as when water seeps into a crack in a rock and then
freezes, expanding and splitting the rock.
Minerals are chemical compounds; thus, whereas physical
weathering attacks the rock as a whole, chemical weathering effects
the breakdown of the minerals that make up the rock. This breakdown
may lead to the dissolution of the minerals, which then are washed
away by water or wind or both, or it may be merely a matter of
breaking the minerals down into simpler compounds. Reactions that
play a part in this breakdown may include oxidation, mentioned
earlier, as well as carbonation, hydrolysis (a reaction with water
that results in the separation of a compound to form a new
substance or substances), and acid reactions. For instance, if coal
has been burned in an area, sulfur impurities in the air react with
water vapor (an example of hydrolysis) to produce acid rain, which
can eat away at rocks. Rainwater itself is a weak acid, and over
the years it slowly dissolves the marble of headstones in old
cemeteries.
The product of weathering in rocks or minerals is
unconsolidated, meaning that it is in pieces, like gravel, though
much less uniform in size. This is called regolith, a general term
that describes a layer of weathered material that rests atop
bedrock. Sand and soil, including soil mixed with loose rocks, are
examples of regolith. Regolith is, in turn, a type of sediment,
material deposited at or near Earth's surface from a number of
sources, most notably preexisting rock.
Every variety of unconsolidated material has its own angle of
repose, or the maximum angle at which it can remain standing. Piles
of rocks may have an angle of repose as high as 45°, whereas dry
sand has an angle of only 34°. The addition of water can increase
the angle of repose, as anyone who has ever strengthened a sand
castle by adding water to it knows. Suppose one builds a sand
castle in the morning, sloping the sand at angles that would be
impossible if it were dry. By afternoon, as wind and sunlight dry
out the sand, the sand castle begins to fall apart, because its
angle of repose is too high for the dry sand.
There are three general processes whereby a piece of earth
material can be moved from a high out-cropping to the sea:
weathering, mass wasting, and erosion. In the present context, we
are concerned primarily with the last of these processes, of
course, and secondarily with weathering, in as much as it
contributes to erosion. A few words should be said about mass
wasting, however, which, in its slower forms (most notably, creep),
is related closely to erosion.
Mechanical or chemical processes, or a combination of the two,
acting on a rock to dislodge it from a larger sample (e.g.,
separating a rock from a boulder) is an example of weathering, as
we have seen. If the pieces of rock are swept away by a river in a
valley below the outcropping, or if small pieces of rock are worn
away by high winds, the process is erosion. Between the
out-cropping and the river below, if a rock has been broken apart
by weathering, it may be moved farther along by mass-wasting
processes, such as creep or fall.
The South
Rock
Your job is to hike to these two rocks and answer some
questions. They are about .35 miles apart, within easy walking
distance, but probably a couple of miles if you were to drive to
each of them. You can get to the North rock from a road starting at
N 40 11.529 W 111 36.739 and you can park pretty close by. You may
need a higher clearance vehicle though I have driven up in my 2wd
mini van. The South rock can be accessed by parking by N 40 10.688
W 111 35.835 and is a short, inclined hike to the rock. Once you
get to the rocks, walk around them and determine how big they are.
Then look at the trails they have made. Try and figure out where
they came from. To log a find you must email me the answers
these questions: (Logs with answers will be
deleted.)
1. Which rock is bigger? North or South
2. Which rock was closest to smashing into houses? North or
South
3. Which rock made the deepest impact crater? North or South