Weathering, also
known as rock decay or stone decay, is the breaking down of rocks
while they sit in one place. Erosion is the transport of the
weathered material. Weathering starts with joints which are cracks
that weaken the rock. The joints make it easier for the rocks to
break down physically or chemically. One of the physical rock decay
processes we see in Estes Park is frost decay or frost wedging.
Frost wedging is common on mountaintops above the treeline. Frost
wedging is the freezing and thawing of water in joints. As water
freezes in the cracks, it expands which creates force that makes the
rock split apart. Another physical decay process we can see in Estes
Park is root wedging. The roots of plants can spread into cracks and
force the cracks to expand. In some areas, we can also see domes that
have been created by pressure release. When
a large rock forms under great pressure, erosion causes slabs of
pressure release shells to pop off of the rock. The rock becomes
rounded over time when multiple pressure release shells pop off.
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The joints make it easier for weathering to take place.
In this image we can see root wedging. Seeds get into the joints and
grow after they absorb nutrients from the rock particles and water.
Trees can't grow above the tree line because the
temperatures aren't suitable. Frost wedging takes place above the
tree line. This is Longs Peak in July of 2014 and in April of 2013.
The edges on the rounded rock show where pressure
release shells popped off.
Biological weathering processes can be seen in Estes
Park. When living organisms contribute to the decay of rock, it is
considered biological weathering. Lichens are a combination of algae
and fungi and they are common in Estes Park. Lichens take minerals
from the rocks through ion exchange. The wetting and drying of
lichens can cause them to expand and contract. Lichens weather rocks
chemically by releasing acids. The loss of minerals through ion
exchange, the expansion and contraction, and the production of acids
can weaken rock and make pieces flake off.
The light green and orange substances on the rock are
lichens.
Sources:
All photos in this post were taken by me, Sylvia Jackson.
Dr. Casey Allen's lecture “Rock Decay”
McKnight's Physical Geography: A Landscape Appreciation,
Edition Eleven by Darrel Hess
http://www.earthonlinemedia.com/ebooks/tpe_3e/mass_movement_weathering/physical_weathering.html
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