Thursday, April 10, 2014


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  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.
Diagram showing construction of sand dunes.  Public Domain.

An outcrop of Navajo Sandstone, Utah, showing cross-bedding indicative of original deposition in a dune field. 
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.
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.

Edge of lava flow south of I-70 along frontage road.
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.

Remnants of the Dotsero Volcano as seen from I-70.  Note layered cinders.
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. 

Topographic map (from 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.

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).


Colorado Historical Society, 2008:

Hutton, James, 1785, concerning the System of the Earth, its Duration and Stability: read before the Royal Society of Edinburgh and published privately.

Smithsonian Institution Global Volcanism Program, 2008:

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