Week Two – Igneous Rocks
Today my wife and I hiked half dome
located in Yosemite National Park, CA.
It is part of the Sierra Nevada mountain range. The Sierra Nevada mountain range formed from
the intrusion of magma from an arc shaped chain of volcanoes that cooled slowly
underground (USGS, n.d.). This intrusion
happened during the Mesozoic are, around 200 to 66 million years ago
(SFCollege, n.d.).
Around 20 million years ago the crust
east of the sierras began to stretch and break up creating the steep valleys
and ranges. Then around 5 million years
ago the huge batholith of mostly granite began to uplift from the Sierra block
and a down drop from the eastern side of the fault. This created a slow rising slope to on the
western face of the mountain range and steep eastern faces (USGS, n.d.). Part of this granite batholith is call
Yosemite National Park that has been formed from erosion, weathering, and
glaciers to form the granite formations such as Half Dome.
The total hike took us 11 hours. We hiked a total of 15 miles ascending about
5,000 feet above the Yosemite Valley and 8,800 feet above sea level. We began the hike at the Half Dome Village around
6 a.m. The overall hike was very
beautiful. We got to see waterfalls,
great views, and get some good exercise.
The culmination came the last 400 feet scaling the summit of Half Dome
(NPS, 2016). It was impressive as we
climbed the summit to think how long it took this rock to form. It began millions of years ago when the magma
beneath our feet slowly cooled to give the rock time to develop large crystals
becoming very hard. This crystallization
formed quartz and potassium fledspar which is the majority makeup of granite (Lutgens
& Tarbuck, 2015) (p. 97 – 98). Then we considered the amount of time it took
for the large monolith to be pushed up to the surface through the process of
plate tectonics along with how much erosion took place to get its dome like
shape. All this reflection gave us a
humbling appreciation for the power and beauty of mother nature.
References
Lutgens,
F. & Tarbuck, E. (2015). Essentials
of Geology (12th ed.). Upper Saddle River, NJ: Pearson
Education, Inc.
NPS. (2016).
Half Dome Day Hike. Retrieved from
SFCollege. (n.d.).
Geological History (Paleozoic, Mesozoic
and Cenozoic). Retrieved from
USGS. (n.d.).
Geology and National Parks. Retrieved
from https://geomaps.wr.usgs.gov/parks/province/pacifmt.html
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