The science of geology has
several principles that are basic to understanding the complex physical world
that we call home. Among the fundamental
doctrines is one geologists term uniformitarianism—“the view that the
interpretations of earth history can be based on the present-day evidence of
natural processes.” From this comes the maxim the “present is the key to the
past.” Although geologists believe the
processes may be the same, the rate of change certainly may/does vary over
geological time. What this means is that
scientists study current geologic processes to understand the rocks and
geomorphic features of the past, an idea first put forth by James Hutton in
1785.
One example of using this
doctrine is to examine modern day sand dunes, such as those at Great Sand Dunes
National Park in the San Luis Valley (see http://www.nps.gov/grsa). Here, the majestic dunes display sand blown
from the west to pile up against the Sangre de Cristo Mountains on the eastern
margin. In cross section, it is quite
easy to observe the inclined bedding so characteristic of dunes. Remembering the Doctrine of
Uniformitarianism, it seems logical to infer that some of the sandstone units, so well exposed in the
Colorado Plateau, were originally deposited in a large Mesozoic dune field.
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| Diagram showing construction of sand dunes. Public Domain. |
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An outcrop of Navajo Sandstone, Utah, showing
cross-bedding indicative of original deposition in a dune field.
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Another example of using the
Doctrine is to examine the modern volcanoes in the State of Hawaii, such as Kilauea. Many of us have seen the great television videos
of this erupting volcano. Viewers have seen the flowing lava, the volcanic
bombs being shot in the air, and the accumulating cinders. Older readers certainly remember May 18, 1980
and the catastrophic eruption of Mt. Saint Helens in Skamania County,
Washington. Therefore, when geologists
see accumulations of volcanic cinders, volcanic ash, and lava hardened into a
rock called basalt, they understand that a volcano has erupted at some time in
the geologic past.
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| The eruption of Kilauea. Public Domain photo. |
Colorado has a number of
sites that display great examples of past volcanoes including the 39 Mile
Volcanic Field (responsible for the ash preservation at Florissant Fossil Beds
National Monument) and the spectacular La Garita Caldera (the site of a
supervolcano) and its tremendous explosions in the Tertiary (see Blog postings November 19, 2011 and October 4, 2012). However, it is nice to study your volcanoes
up close and personal and in Colorado that would be the Dotsero Volcano.
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Edge of lava flow south of I-70 along frontage
road.
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Thousands of people drive
by the small community of Dotsero (Mile Marker 133 west of Vail) everyday as
they busily traverse Interstate 70. Most
do not realize that adjacent to the Interstate is a nice compact volcano that
is readily accessible by auto. In
addition, few understand the road crosses the lava (basalt) field created by
the eruption.
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Remnants of the Dotsero Volcano as seen from
I-70. Note layered cinders.
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The volcano is classified by
the Smithsonian Institution (2008) as a maar and scoria cone. Scoria is a type of volcanic rock that has
numerous vesicles or open spaces and is quite “light” in weight. A maar volcano is caused by groundwater
coming in contact with the hot lava. The
maar at Dotsero is a “700 m wide and 400 m deep” crater that erupted about 4150
radiocarbon years ago—2200 BC +/- 300 years (Smithsonian Institution,
2008). The resulting basaltic lava flow
traveled south down a small valley and crossed the floodplain of the Eagle
River and actually caused the River to move its course to the south side of the
valley, something easily seen on maps and air photos. A frontage road south of I-70 allows one to
drive to the flows for a close examination, while a frontage road north of the
Interstate will get you to the volcanic maar.
Unfortunately, a commercial mining company has destroyed much of the
volcano in its search for decorative cinders.
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Topographic map (from
mapcard.com) showing location of Dotsero Volcano, and the lava flow near
I-70. Note southward bend in Eagle River
(parallel to DRGW railroad). Lava flowed
down valleys from the crater.
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I have always noticed the
small community of Dotsero due to its relationship with F.V. Hayden. This famous geologist was mapping parts of
western and central Colorado in the 1870s and designated the area as dot-zero
on his maps. That notation later became
Dotsero.
Hence we are led to conclude, that the greater part of our land, if not the whole had been produced by operations natural to this globe (Hutton, 1785).
REFERENCES CITED
Colorado Historical
Society, 2008:
http://www.coloradohistory.org/exhibits/ancientvoices.htm
Hutton, James, 1785, concerning
the System of the Earth, its Duration and Stability: read before the Royal
Society of Edinburgh and published privately.