Volcanic Rocks near Project Faultless
A
cache
by GeoEdYOUcation
Hidden:
11/15/2006
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Visit this site where Cold War era underground nuclear testing
caused subsidence of the ground along faults that cut volcanic
rocks called ignimbrites or ash-flow tuffs. These rocks were
deposited during violent volcanic eruptions about 30 to 33 million
years ago, during the Oligocene Epoch of the Tertiary Period.
Geologists identify these rocks as rhyolite and rhyodacite by their
mineralogy (rich in quartz, sanidine, plagioclase, biotite, and
hornblende) and chemistry (rich in silica).
On January 19, 1968, the U.S. Atomic Energy Commission (the
forerunner of the Department of Energy) detonated a nuclear bomb in
a borehole at a depth of 975 meters (3,200 feet) below the large
metal pipe that protrudes from the ground near this site, part of
the Central Nevada Test Area. The device, with an announced yield
of between 200 kilotons and one megaton, was detonated (a) to
determine the environmental and structural effects that might be
expected should subsequent higher yield underground nuclear tests
be conducted in this vicinity and (b) to study the behavior and
characteristics of seismic signals generated by nuclear detonations
and to differentiate them from seismic signals generated by
naturally occurring earthquakes. No further tests were conducted
near here, but more than 900 bombs were tested on the Nevada Test
Site farther to the south. The test caused the ground to break,
ironically, given the name of the shot – Project Faultless,
creating new faults when the area close to ground zero sank into
the underground cavity created by the blast. The collapse created
numerous surface fractures up to 2,743 meters (9,000 feet) in
length, with vertical fault displacements up to 5 meters (15 feet)
and horizontal offsets up to 1 meter (3 feet).
Radioactivity from the blast was kept underground, although the
U.S. Department of Energy and the Nevada Division of Environmental
Protection are studying whether radioactivity could escape through
groundwater flow.
The material at the surface is Quaternary (less than 1.8 million
years old) alluvium – unconsolidated sediment eroded from older
rocks. The rocks in the hills nearby to the west are dominantly
ignimbrites (also called ash-flow tuffs), erupted violently from
volcanoes about 30 to 33 million years ago, during the Oligocene
Epoch of the Tertiary Period. Geologists identify these rocks as
rhyolite and rhyodacite by their mineralogy (rich in such minerals
as quartz, sanidine, plagioclase, biotite, and hornblende) and
chemistry (rich in such elements as silica, potassium, and sodium
and poor in such elements as magnesium, calcium, and iron relative
to other common igneous rocks).
The nuclear test occurred in tuffaceous sediments (sandstones
and siltstones derived from volcanic material) and nonwelded tuff
that was altered to zeolite minerals millions of years ago. The
alluvium above these rocks is 732 meters (2,400 feet) thick.
The site is monitored by both the U. S. Department of Energy and
Nevada Department of Environmental Protection for any traces of
radionuclides in air or groundwater. The environmental monitoring
program is described in detail in the website links given
below.
To log this EarthCache:
At the coordinates given is a prominent fault scarp that formed
after the explosion, caused when the ground dropped down along the
break in slope. The scarp is recognizable because vegetation has
not completely re-established itself along the fault scarp. In
order to log this Earthcache site, determine which side of the
fault scarp moved down (N, E, S, or W) relative to the other side
and e-mail the answer to the site developer along with a photo of
your group at the site, if possible. Please tell us how many people
were in your group visiting this Earthcache site.
REFERENCES:
Kleinhampl, F.J., and Ziony, J.I., 1985, Geology of northern Nye
County, Nevada: Nevada Bureau of Mines and Geology Bulletin 99A,
171 p., with maps at 1:250,000 scale.
(visit link)
(visit link)
SPECIAL NOTES ABOUT ACCESS AT THIS SITE
Hiking is easy in this area.
CAUTION IN USING GPS UNITS AND TOPOGRAPHIC MAPS
(Note that GPS coordinates are relative to a particular datum
used to describe the nearly spherical shape of the Earth’s surface.
Most topographic maps published by the U.S. Geological Survey use
the North American Datum of 1927 (NAD 27), but most GPS units are
set for either the North American Datum of 1983 (NAD 83) or the
World Geodetic System of 1984 (WGS 84). NAD 83 and WGS 84 give
nearly identical locations with hand-held GPS instruments, but NAD
27 can be off considerably. In this part of Nevada, there is little
change in latitude between the 1927 and 1983 data, but for
longitude the datum of 1983 is shifted relative to the datum of
1927, such that, if you use your GPS unit to measure a location
using WGS 84, the point will plot on the U.S. Geological Survey
topographic map approximately 100 meters farther east than its true
location on the map. If your GPS unit is set to NAD 27, you need to
look for the WGS 84 waypoint approximately 100 meters farther east
from your location.)
BASIC VISITOR-USE AND PUBLIC SAFETY INFORMATION FOR PUBLIC LANDS IN
NEVADA:
All visitors need to plan ahead and prepare for outings in
Nevada’s public lands by:
• Knowing the regulations and special concerns for the area you are
planning to visit (obeying laws that prohibit collection or
destruction of artifacts);
• Carrying a map and a GPS unit and/or compass (Maps are available
for purchase at all BLM offices and from the Nevada Bureau of Mines
and Geology, www.nbmg.unr.edu.);
• Staying on existing roads and trails;
• Staying away from all mine shafts and adits;
• Planning for extreme weather, hazards, and emergencies;
• Carrying a full-size spare tire, extra food, water, and warm
clothing;
• Being aware that cell phones DO NOT usually work in the rural
areas away from the major highways;
• Leaving your travel plans with a responsible party, including the
date and time of your return;
• Linking to “Tread Lightly and Leave No Trace” websites
(www.treadlightly.org and www.lnt.org).
Please see www.nbmg.unr.edu/EarthCache.htm for more information
about this and other Nevada EarthCache and GeoCache sites of
geologic interest. Thank you.
Additional Hints (
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Find...
 Closer view of fault scarp
Closer view of fault scarp caused by underground nuclear detonation at Project Faultless.
Faultless fault
Fault Scarp caused by underground nuclear detonation at Project Faultless.
Ground Zero Plaque
Plaque commemorating Project Faultless detonation.
Project Faultless remains
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