DOTSERO VOLCANO & UNIFORMITARIANISM

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.

 

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 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.

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.

Smithsonian Institution Global Volcanism Program, 2008: http://www.volcano.si.edu/world/volcano.cfm?vnum=1208-01-

GOING TO TUCSON: ROAD LOGS

Geologic road logs are some of the most useful tools field geologists and rockhounds have at their disposal.  These logs describe geologic features and stratigraphy, at specific mileages, that are visible along the road in question.  In the pre-electronic age most road logs were printed in guidebooks published by various geological societies (and these remain a wealth of information so check at your local academic library).  I have  found these roads listed below useful and interesting as I make annual visits to the Tucson "show."

Rockhounds take note: as usual, be careful, take the necessary precautions when traveling, do not trespass on private land, and know the local collecting regulations.

COLORADO PLATEAU TO GREAT BASIN http://www.aipg.org/2008/Phoenix%20to%20Flagstaff%20Road%20log.pdf

The road log describes the geology from Flagstaff, located in the pine trees of the Colorado Plateau, down elevation through the Transition Zone, and into the Sonoran Desert of the Basin and Range.

KAYENTA TO MEXICAN WATER, ARIZONA: http://www.fourcornerssw.com/kayenta_to_mexican_water__ariz.html

Monument Valley in the northern part of Arizona occupies a prominent place on many travelers’ bucket list.  The road logs follow Jurassic and Cretaceous rocks exposed on the mesas and in the drainages.  The bonus exposures include the numerous igneous rocks called diatremes.

THE APACHE TRAIL: http://repository.azgs.az.gov/uri_gin/azgs/dlio/1007

Readers will need to locate this web site then click on the hot link Guidebook 4-Highways of Arizona.  Although this log is about 40 years old, it gives a nice tour of the Apache Trail from the city of Apache Junction north by the Superstition and Goldfield Mountains to the campground and marina at Canyon Lake.

ISINGLASS AND MUSCOVITE: BLACK HILLS

What is it?  Width ~7 cm.

As a kid growing up in Kansas I was always interested in the sciences and especially in the “natural world.”   I always wanted to become a Forest Ranger, mostly due to my love of the “outdoors” and the correspondence school advertisements in publications such as Field and Stream.  I wanted to go out and measure giant trees and trap wild beaver and wear those knee-high, lace-up boots.  In the right jobs you could also wear the flat-banded Smoky the Bear Hats.  I also unmercifully quizzed my father about hills and streams and trees and mountain lions.  He answered to the best of his ability but certainly had no formal training in the sciences.  At any rate, he was fond of calling one local spot “Isinglass Hill” due to shiny clear crystals in a black shale reflecting sunlight.  Furthermore, I learned that isinglass (Muscovy Glass in Russia) was used as windows in the older model natural gas heating stoves.  I was duly impressed and asked to stop and collect, which we did.  The crystals were small and did not seem large enough for stove windows.  But, oh well I was certain that bigger crystals were found in other hills. 

OK, on a field trip to Isinglass Hill several years later in an introductory geology class, I learned that my father was only “half-right.” Isinglass is used as a stove window; however, the crystals in the hill (Cretaceous: Graneros Formation) were selenite gypsum!  But, hold on.  As they say in the movies, "maybe the old man was right", or at least he was not dreaming up something!  Modern maps do not show an Isinglass Hill in Ellsworth County; however, a 1918 Atlas has a location for Isinglass Hill Farm in Carneiro Township along the Union Pacific Railroad.  That is good enough for me.  Trust your father! Isinglass is a mica-mineral, usually muscovite [KAl2(AlSi3O10)(OH)], and at one time was mined at many places in the United States including North Carolina and the pegmatites of the Black Hills of South Dakota.  I find the latter pegmatites fascinating and often wish that I was more of a mineralogist/petrologist.  Norton and Redden (1990) believed there were somewhere near 20,000 pegmatite bodies located within the Precambrian Harney Peak Granite (the Granite is home to Mt. Rushmore).  And, several of these bodies were mined early in the Hills’ mining history---for stove windows.  As I understand, the McMackin Mine started producing sheet mica in 1879.  To put that date in perspective, it was only five years before (1874) that Lt. Colonel George Custer “discovered” gold in the Blacks Hills and three years (1876) since he lost his life at the Battle of the Little Bighorn. Mica is not really a mineral but the name of a group of sheet-like phyllosilicate minerals (www.Mindat.com lists 45 or so), the most common being muscovite (potassium-rich), biotite (iron-rich), phlogopite (magnesium-rich), and lepidolite (lithium-rich).  Muscovite in the Black Hills has been mined as scrap mica, small pieces that were later shred and ground, and used in paints, roofing, concrete and mortar, caulking, fireproofing, lubricants, and host of other applications. At one time the Hills produced something like one-third of the nation’s mica.  As far as I know, Pacer Minerals in the small Hills town of Custer is the only producer left in the area. Sheet mica consists of large sheets of muscovite and was used in insulating radios, fuse boxes, lamp sockets, and other types of electronics (and stove windows).  Westinghouse Electric arrived early in the history of mica mining and operated four or five mines near Custer.  It is my understanding (from visiting with local collectors) that thousands of pounds of mica were produced as part of the “war effort” (World War II) but that need almost evaporated after the war.  Roberts and Rapp (1965) reported that a book of mica at the White Spar Mica Mine measured three feet wide by four feet long.  I have not collected anything that large but certainly have noted isolated sheets five inches by five inches (no visible crystal faces).  Since muscovite has perfect basal cleavage, a knife may be used to cleave quite thin sheets. One of the interesting byproduct of the early electronics industry around Custer is the presence of muscovite sheets that have been “punched out.”  That is, some sort of a machine, presumably hand-operated, punched out specific shapes of muscovite that were then used as insulators (again I presume).  Local collectors were uncertain about the exact age of the specimens but “thought” World War II.  These pieces are sometimes available on local hillsides or near the factory (that was pointed out to me by a collector).  I have four of these punched out sheet mica and they add a distinct flavor to my collection.    Width ~7 cm. Width ~7 cm. By-the-way, later in life during the summers of 1971, 1972, 1973, I served as a seasonal Park Ranger Naturalist at Dinosaur National Monument.  Thus, I achieved one of my boyhood dreams of wearing a Smokey the Bear hat.  I still have that hat as it brings back many pleasant memories. REFERENCES CITED Norton, J.J. and J.A. Redden, 1990, Relations of Zoned Pegmatites, Granite, and Metamorphic Rocks in the Southern Black Hills: American Mineralogist, v. 75. Roberts, W.L. and G. Rapp Jr., 1965, Mineralogy of the Black Hills:  South Dakota School of Mines Bulletin 18.