by Robert Verish
by Robert Verish
The "Elko Crater Field" Revisited - A Reconnaissance Report
When I first heard about the "Elko Crater Field" I immediately thought, "This is too good to be true!" Could there really be a large swath of small craters in Northern Nevada that few people have heard about AND that the meteorites have yet to be found? That was back in the fall of 2000. And now I think I have an answer to that question. But what has me convinced is that these "craters" need much more study. And not just because these are rare and unusual geomorphic features, but, because they May be terrestrial analogs for similar features thought to be evidence for groundwater on Mars!
I first heard about these "meteorite craters" from my friend and colleague, Kris Henkel. He first learned about these while doing an Internet search on "craters", and when he contacted me, he was preparing to visit the site. Kris told me about his research on these "craters", up to that point in time. He said that he was going to take a magnetometer with him on his initial visit. He explained that there was a web page for this area on the BLM - Elko Field Office web site, and that this was what came up in his web search results. This web page made reference to a USGS study of this part of Elko County, which resulted in the publication of a geologic map sheet, called MF-1168, which was dated 1980. I told Kris that I would go to the Cal Tech library, get a copy of this map sheet, and contact the authors (Keith B. Ketner and David J. Roddy).
Kris didn't find any evidence of meteorites on his initial visit, but his
description of this area gave me confidence that a meteorite find could be made.
I had lengthy discussions with both of the authors, Ketner and Roddy, and
although they never found any direct evidence of meteorites, they both felt that
an impact was the best explanation for these "craters". This boosted my
confidence that Kris and I would be successful at finding meteorites. The
authors gave us their blessing to conduct a search in their 1980 study area, and
wished us good luck. I promised them that they would be contacted immediately if
any meteoritic evidence were to be found. They also agreed to my suggestion that
the BLM web page be taken down until evidence confirming the meteoritic nature
of these craters could be found. The Elko BLM Office was very prompt in
complying with our suggestion. (To this day, several web sites still have links
to this still "removed" BLM web page: http://www.nv.blm.gov/elko/meteor/meteor.htm)
Unfortunately, Kris Henkel's magnetometer survey and my reconnaissance of the area failed to uncover any "meteoritic evidence", so we never had the opportunity to report back to the original authors. And then David Roddy passed away in May of this year. Concerned that the scientific interest in these "craters" would pass away with Dr Roddy, I felt compelled to find a way to bring renewed attention to the "Elko Crater Field". I attempted this by writing an abstract and presenting a poster at the Denver 2002 GSA Meeting:
My Abstract:
"ELKO CRATER FIELD" REVISITED - RECONNAISSANCE REPORT
My Poster:
Poster Presentation at GSA Meeting
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(Large file, please allow time for the image to download)
By
Robert S. Verish
P.O. Box 237, Sunland, California, 91041, bolidechaser@yahoo.com
USGS Map Sheet
MF-1168 by Ketner & Roddy (1980) is entitled "Map Showing the Elko Crater
Field, Elko County,Nevada".
This poster reports on a subsequent field survey of this "Elko Crater Field".
This survey was conducted during Spring of 2001, and was intended to be only a
reconnaissance effort for the purposes of securing evidence of ejecta or
meteoritic material, and to examine the stratigraphy of the craters. This
survey did not result in any finds of ejecta or meteoritic material.
A
close inspection of the stratigraphy of the "crater rims" did not reveal any
evidence of disordered layering. All of the above is considered as negative
evidence for an impact origin for the Elko Crater Field. An exposure that is
nearby a cluster of "craters" in the Susie Creek area revealed evidence, which
affords an interpretation for a terrestrial geologic origin for all of these
depressions. A thin (~1m) veneer of colluvium overlies a section of
volcaniclastic sediment that can be divided into an upper and lower unit. The
upper unit (~20m) is a light brown to tan-colored coarse sand that is
interbedded with thinly layered, fine-grained tuff. The lower unit is
predominantly a greenish-gray bentonitic (expansive) clay. The base of the
lower unit is not exposed in the Susie Creek area, but where the tributaries
come in contact with this unit, a flat-floored streambed is produced. The
"craters" only occur within exposures of this formation. In addition, many
small landslides and soil slumps are in evidence throughout the Susie Creek
area. The Elko Craters are interpreted by this writer as being a subsidence
feature within the "upper" volcaniclastic unit, the result of groundwater
sapping of the "lower" bentonite-rich unit. Typically, these depressions are
rimmed by the uppermost "veneer" of cobble-rich colluvium which (in a process
that is still not clear) armors the rim against erosion, giving the appearance
that the rim is "raised". Regardless of whether this interpretation is valid,
the Elko Crater Field is a unique and geologically striking feature that
requires additional investigation. Should this interpretation have some merit,
and given the ease these features can be discerned in satellite imagery, there
is the implication (if similar conditions can exist on Mars) that features
originally interpreted as being craters May actually be depressions produced
through subsidence by groundwater sapping.
2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 239--Booth# 104
Impact Stratigraphy (Posters)
Colo. Convention Center: Exhibit Hall
The main thrust of my poster presentation was that the unusual and unique features in the "Elko Crater Field" were worthy of closer examination, and that a properly funded geomorphology study May show that these "craters" were formed by subsidence through the process of groundwater sapping. The significance of this is that this type of subsidence could be a terrestrial analog for similar features on Mars, thus becoming additional evidence for the existence of groundwater on that planet.
It wasn't until after I submitted my abstract for publication that I ran across an abstract by Jim Richardson (U. of Az - LPL), with a subject related to "groundwater sapping". This, in turn, led me to his web site and to his other soon to be published papers on this subject. [See links below.]
The following web pages by Jim Richarson will require the use of the latest version of Adobe Acrobat Reader:
Jim Richardson's Abstract:
http://www.lpl.arizona.edu/conferences/lplc/abstract_volume/richardson.pdf
His Presentation:
http://www.lpl.arizona.edu/~jrich/work/nirgalprofile3.pdf
His Paper with References:
http://www.lpl.arizona.edu/~jrich/work/nirgalprof1.pdf
APPENDIX:
A Local
Northeastern Nevada Web Site with a reference to the "Elko Crater Field":
Meteorite Impact
Field, Elko County, Nevada
A More Recent
Web Site with a dedication to David Roddy:
Welcome To
ElkoCraters.Com!!!
A Poster Session
at the Denver 2002 GSA Meeting:
Impact Stratigraphy (Posters)
REFERENCES:
Matching Results About "U.S.G.S Map MF-1168":
1.
Geologic Maps of Nevada
... These selected USGS Geologic Maps are provided through the courtesy of
AngloGold. ... 1:48000. MF-1168. Map showing the Elko Crater Field, Elko Co.,
Nevada. 1 ...
http://keck.library.unr.edu/data/GEOLMAPS/geolmaps.htm
2. GEOLMAPS
... 1980, MF, 1168. NV, ELKO EAST QUADRANGLE, ELKO COUNTY ... 1988, I, 1826.
NV, SURFICIAL GEOLOGIC MAP OF THE ... GQ, 503. NV, TIPPIPAH SPRING QUADRANGLE,
NYE COUNTY,...
http://www.whitman.edu/penrose/govdocs/GEOLM9.html
...The results of future investigations in this study area will most likely appear first in David's Welcome To ElkoCraters.Com!!! web page - so, make sure that you bookmark that one for future reference...
"Disclaimer": No Government/Public Funds were used in the course of this investigation. All funding for this study, including the cost of publishing the results, came from my own, personal out-of-pocket expenses.
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