Mechanical weathering is the process of changing the size and shape
of rocks and minerals. No chemicals are added or removed from the
rock. Roots grow in cracks and break rock. Water freezes and
expands and cracks rocks. Heating and cooling of rocks cause them
to contract and expand, breaking them further. This typically
results in sharp, jagged edges. Water picks up pieces of broken
rock and other debris and hits the bedrock causing abrasion and
polishing both surfaces making them smooth. Water flowing faster
picks up more material. As water slows, it drops off weathered
material: biggest first and smaller pieces flowing further
downstream.
Chemical weathering is where minerals are added or taken away
from rocks. Salt dissolves and washes away. Water is added to
feldspar to make Kaolin. Calcium is dissolved by mild acid. These
chemicals are left behind when water evaporates, creating new rocks
in both locations. Oxygen reacts with rocks with iron and oxidizes
or rusts, creating a new form of mineral. Chemical weathering
typically leaves holes, pools and channels where minerals
susceptible to chemical altering have been dissolved and
removed.
About 1.5 billion years ago, the area known as the Piedmont was
in a shallow ocean and sediment was deposited. About 700 million
years ago, a continental collision between North America, Europe
and Africa occurred building at that time the largest mountain
range in the world. When the continents split, the area was once
again submerged and layers of sediment covered the ocean basin.
About 500 million years ago, the last of the collisions occurred
creating the supercontinent Pangaea and the Appalachian Mountains.
The area we call Piedmont was folded, twisted and turned over on
itself.
Imagine two cars colliding at high speed. The hoods will be
bent, twisted and folded in many unusual patterns. Most of that
folding and twisting is not reversible, just like the land we stand
upon. The flat layers that once were on the bottom of the oceans
were twisted and folded, making ridges. Over time, other sediments
filled in the ridges and metamorphosis changed the types of rocks.
Chemicals were added and removed. Dissolved salts and calcium were
left in thick layers and made calcite, stibnite and other soft,
easily weathered rock. Scientists suspect that about 200,000 years
ago, this area was once again under water and a thick layer of
sediment was deposited on the ocean bottom. Once the water receded
or the land rose, the current weathering and erosion process that
has made our landscape today started.
Plants grew in the sediments and contributed organic matter.
Thick forests grew and changed the soil. One last cold period came,
lasted 30,000 years and left about 9,000 years ago. The current
types of trees were established. The current soil began to form.
The weathering process for the current landscape was
established.
When you get to the site, you will see a waterfall flowing over
some grey rock. There are a series of pools and small falls along
this creek. Examine the rock, pools, and channels and answer the
following questions.
Logging requirements: email to the CO the answers. Do not post
your answers in your log, even encrypted.
1) The first line list Agents of Change: Resistance is Futile
GC385GX
2) Are the rock outcrops perpendicular or parallel to the flow
of water? Why do you suppose water is flowing where it is
flowing?
3) What is the main source of weathering currently: mechanical
or chemical? Why do you say so? What evidence do you see?
4) What do you suppose caused the many series of falls and pools
in this location?
5) The exposed rock is part of the original crustal material,
rich in iron and magnesium. What weathering process will take place
next?
6) Optional but recommended: take and post a picture of you and
your GPS near the falls! Makes a good profile picture!
Congrats to birchtr and rootbeer001 on the FTF
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