Fulgurites
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What are
fulgurites and where can they be found?
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by Carl Ege
Sand
fulgurites found on the top of Mount Raymond. U.S. quarter for scale.
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Most people have never seen a fulgurite, and many that have probably
did not realize what it was at the time. Fulgurites are natural tubes or
crusts of glass formed by the fusion of silica (quartz) sand or rock from
a lightning strike. Their shape mimics the path of the lightning bolt as
it disperses into the ground.
All lightning strikes that hit the ground are capable of forming
fulgurites. A temperature of 1800 degrees Celsius is required to
instantaneously melt sand and form a fulgurite (most lightning strikes
have a temperature of 2500 degrees Celsius). Fulgurites have been found
worldwide, but are relatively rare.
Two types of fulgurites have been recognized: sand and rock
fulgurites. Sand fulgurites are the most common and are generally found in
beach or desert regions containing clean (free of fine-grained silt or
clay), dry sand. They resemble roots or branching tube-like structures
that have a rough surface, covered with partially melted sand grains.
Sand fulgurite tubes have a glassy interior, due to rapid cooling and
solidification of the sand after the lightning strike. The size and length
of a fulgurite depends on the strength of the lightning strike and the
thickness of the sand bed. Many sand fulgurites average 1 or 2 inches in
diameter and can be up to 30 inches long. Sand fulgurites have been found
in Utah’s deserts and on top of some of the higher summits of the
Wasatch Range.
Rock
fulgurite (circled in white) found on quartzite at the summit of Mount
Raymond in the Wasatch Range, Salt Lake County, Utah. Hammer for
scale.
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Coatings or crusts of glass formed on rocks from a lightning strike
are called rock fulgurites. These fulgurites are found as veins or
branching channels on a rock surface or lining preexisting fractures
within the host rock. Rock fulgurites are primarily found on the top or
within several feet of mountain summits.
Mountain peaks are natural lightning rods that are repeatedly blasted
by lightning strikes during severe weather. Rock fulgurites can be found
throughout many of the mountain ranges of the world, including the French
Alps (Mont Blanc), Pyrenees Range, and western U.S. mountains such as the
Sierra Nevada, volcanic peaks of the Cascade Range, Rocky Mountains, and
Utah’s Wasatch Range.
While hiking in the summer of 2003, I discovered both sand and rock
fulgurites on some of the higher summits of the Wasatch Range. I observed
very small sand fulgurites (an inch or less) in some of the surface float
on top of Mount Raymond (10,241 feet) and Broads Fork West Twin (11,328
feet).
I also found rock fulgurites on top of Mount Raymond, Broads Fork West
Twin, Mount Baldy (11,068 feet), and Mount Timpanogos (11,749 feet). Some
of the rock fulgurites, such as those found on Mount Timpanogos, are the
result of human activity (a steel shelter placed on top of the peak
attracts lightning).
In the Wasatch Range, rock fulgurites appear to be confined to
mountaintops composed chiefly of quartzite, but summits consisting of
other rock types could have them as well.
So, the next time you go hiking or exploring be on the lookout for
fulgurites! It is very possible new fulgurite discoveries await the
adventurer on many of the higher summits and desert areas of Utah
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There are businesses selling fulgurites. Here are details from one of them.
FULGURITES
Lechatelierite Var. Fulgurite is the varietal name given to fused Quartz, Si02,
which has been fused by the action of lightning striking the Earth and locally
melting the sand. The best known Fulgurites are found in Quartz sands, where the
Fulgurites take the form of tubes, sometimes exceeding a half inch or more in
diameter. This type of formation is called a Sand Fulgurite. As the
lightning strikes the Earth and courses downward through the sand, the sand is
instantly super heated (i.e., melted and fused). After cooling, glass-like
hollow tubes (Fulgurites) can sometimes be located beneath the surface of the
sand, generally decreasing in diameter and sometimes branching as they descend,
sometimes extending for several feet. The outer surfaces sand fulgurites are
often rough with adhering, unfused Quartz sand grains. The inner surfaces and
openings of the tubes are usually smooth and glassy, in some specimens
resembling an applied glaze, sometimes with blister-like bubbling present.
Rock Fulgurites are formed when lightning strikes the surface of a rock,
melting and fusing the surface, and sometimes the interior of the rock.
The melting point of Si02 is 2950oF. The color of the
glassy, fused Si02 varies from pale gray, to smoky gray, to shiny
black. The name Fulgurite is from the Latin: FULGUR (lightning).
In addition to having been found in terrestrial Fulgurites, Lechatelierite
(natural fused Silica, Si02) has also been identified in the
glass-like particles found in Tektites. This includes Australites, Darwin Glass,
Indochinites, Javanites, Libyan Desert Glass, Moldavites, Philippinites,
Bediasites, Muong Nong-type glass, and Aouelloul crater glass (Impactite).
Lechatelierite is not present in Obsidian, a terrestrial glass-like material
associated with volcanic activity.
SOURCE
Here is text from a lecture about fulgurites.
LIGHTNING MAKES GLASS
Vladimir A. Rakov
University of Florida, Gainesville
1. Introduction
Mother Nature makes glass each time a large amount of energy
is released during a sufficient period of time at the Earth's surface, provided
that the soil composition is suitable for making glass. The latter condition is
satisfied, for example, by sandy soil, with the resultant natural glass being
silica glass named "lechatelierite" after the French chemist Henry Le
Châtelier (1850-1936). There are two phenomena that are responsible for making
natural glass on Earth: meteorites and lightning. Glass that is made as a result
of the collision of a meteorite with the Earth's surface is called meteoritic
glass or tektite. Glass (a glassy object, to be exact) that is made as a result
of a cloud-to-ground lightning discharge is called a fulgurite (from the Latin
"fulgur" which means lightning). Fulgurites come in a great variety of
forms and can be viewed as nature's own works of art. It is worth noting that
lechatelierite (natural silica glass) is not present in obsidian, a glass-like
material associated with volcanic activity. On the other hand, volcanic activity
is known to generate lightning which, if it strikes sandy soil, may produce a
fulgurite. Silica glass has been also made as a result of nuclear explosions. In
1945, the first nuclear bomb (equivalent to 18,000 tons of TNT) was detonated in
the New Mexico desert. The explosion formed a crater 800 yards in diameter,
glazed with a dull gray-green silica glass. This glass was named "trinitite"
after Trinity Site where the first nuclear bomb test was conducted.
2. Characterization of Lightning
On average, about 100 lightning discharges occur every
second on the Earth. Only about one-third of them involve ground (others occur
in the cloud, between clouds, or between cloud and clear air) and potentially
can make fulgurites. The Tampa area in Florida receives more than 12 lightning
strikes per square kilometer per year. This is the highest level of lightning
activity in the United States.
Each cloud-to-ground lightning involves an energy of roughly
109-1010 Joules. Most of the lightning energy is spent to
produce thunder, hot air, light, and radio waves, so that only a small fraction
of the total energy is available at the strike point. However, it is well known
that this small fraction of the total lightning energy is sufficient to kill
people and animals, start fires, and cause considerable mechanical damage to
various structures. Lightning is also a major source of electrical disturbances.
The peak temperature of lightning channel is of the order of
30,000° K, which is five times higher than the
surface temperature of the Sun (the temperature of the solar interior is 107
K). The lightning peak temperature is considerably higher than silica's melting
point which is somewhere between 1600 and 2000° C
depending on moisture content, but whether or not silica sand melts and glass is
produced depends, besides other, not well-understood factors, on lightning
duration. Some lightning strokes last (since a contact with ground is made) for
less than a millisecond, others linger for a significant fraction of a second.
Lightning current peaks are usually of the order of tens of kiloamperes, but
occasionally may exceed 100 kA. The long-lasting current components are
typically in the range of tens to hundreds of amperes. The latter are thought to
be responsible for making fulgurites.
In the case of natural lightning, it is usually unknown when
and where the discharge is going to occur. These uncertainties are largely
removed when lightning is artificially initiated (triggered) from an overhead
natural thundercloud with the so-called rocket-and-wire technique (for details
visit our Web Site: http://www.eel.ufl.edu/~lightning). Some of the most
interesting fulgurites have been created in triggered-lightning experiments.
About 30 to 40 lightning discharges are triggered every
summer at the International Center for Lightning Research and Testing (ICLRT) at
Camp Blanding, Florida. The Center is located approximately midway between
Jacksonville and Gainesville, Florida, and is a unique facility for studying
various aspects of atmospheric electricity, lightning, and lightning protection.
The Center is operated by the University of Florida (UF). Examples of still
photographs of lightning flashes triggered at Camp Blanding, Florida, are shown
in Fig. 1. During summers of 1995 through 1998 over 30 scientists and engineers
(excluding UF faculty, students, and staff) from 13 countries representing 4
continents performed experiments at the Center. Many triggered lightning
discharges at the Center, that terminated on ground (as opposed to termination
on well-grounded objects or systems) created fulgurites.
3. General Information on Fulgurites
The earliest discovery of a fulgurite was reportedly made in
1706 by Pastor David Hermann in Germany. Most people have never seen a fulgurite,
and if they have they might not have recognized it for what it was. All
fulgurites can be divided in two classes: sand fulgurites and rock fulgurites.
Sand fulgurites are usually hollow, glass-lined tubes with sand adhering to the
outside. Rock fulgurites are formed when lightning strikes the bare surface of
rocks. This type of fulgurite appears as thin glassy crust with which may be
associated short tubes or perforations lined with glass in the rock. Glass of
this type may be relatively low in silica and exhibit a wide variety of colors,
depending on the composition of the host rock. Rock fulgurites are found on the
peaks of mountains.
When lightning strikes sandy soil, the air and moisture
present in soil are rapidly heated, and the resultant explosion-like expansion
forms the central tubular void. As stated before, quartz sand melts at a
temperature of about 1600-2000° C depending on
moisture content, and molten glass is pushed to the periphery of the void.
Subsequent relatively rapid cooling causes the glass to solidify. A general
condition for sand fulgurite formation appears to be the presence of a
relatively dry dielectric such as quartz sand overlying a more conducting soil
layer or the ground water table, with the depth of the latter probably
determining the limit for vertical extent of the fulgurite formation. The
diameter of fulgurites ranges from a quarter of an inch to 3 inches, and the
color varies, depending upon the type of sand from which they were formed. Sand
fulgurites are usually tan, grayish, or black, but almost translucent, white
fulgurites have been found in Florida pan-handle beaches. The inner surface is
glassy and exhibits numerous bubbles. The walls are usually about 0.5-2 mm
thick, but may be paper thin. There appears to be no relation between tube
diameter and wall thickness. Sand fulgurites are quite fragile and very
difficult to excavate in one piece. An example of sand fulgurite is shown in
Fig. 2.
Since fulgurites are real glasses, they are very resistant
to weathering and are usually well preserved for a long period of time. For this
reason they are used as paleoenvironmental indicators. For example, many
fulgurites are found in the Sahara desert, where presently there is little
lightning activity, confirming that very different conditions existed in this
region in prehistoric times. A fossil fulgurite thought to be 250 million years
old has been reported.
Fulgurites have been also produced artificially passing
laboratory arc current through sand. It has been found by researchers at the
Technical University of Ilmenau, Germany, that currents higher than 50 kA
lasting for some hundreds of microseconds, typical of impulsive components of
the lightning current are incapable of making a fulgurite (only some very thin
fragments). On the other hand, relatively low magnitude currents of some
hundreds of amperes lasting for some hundreds of milliseconds yielded
well-formed fulgurites with diameters of 7 to 15 mm. It has been also observed
that the higher the current the larger the cross-sectional dimensions of
fulgurite. Different forms of fulgurites were obtained in dry and wet sand.
Fulgurites in wet sand were more curved and had more irregular outer surface.
The latter feature was attributed to the pressure of vaporized moisture that
squashed the fulgurite when the arc pressure in the central tubular void
disappeared, while the glass was still plastic.
4. Fulgurites Created at the ICLRT at Camp Blanding,
Florida
4.1. Underground Power Cable Project (1993-1994)
In 1993, an experiment, sponsored by Electric Power Research
Institute (EPRI), was conducted by Power Technologies, Inc. to study the effects
of lightning on underground power cables. In this experiment three 15 kV coaxial
cables with polyethylene insulation between the center conductor and the outer
concentric shield (neutral) were buried 5 m apart at a depth of 1 m, and
lightning current was injected into the ground at different positions with
respect to these cables. One of the cables (Cable A) had an insulting jacket and
was placed in PVC conduit, another one (Cable B) had an insulating jacket and
was directly buried, and the third one (Cable C) had no jacket and was directly
buried. About 20 lightning flashes were triggered directly above the cables
which were unenergized.
The underground power cables were excavated by the
University of Florida in 1994. The damage found ranged from minor punctures of
the cable jacket to extensive puncturing of the jacket and melting of nearly all
the concentric neutral strands near the lightning attachment point. Some damage
to the cable insulation was also observed. In the case of the PVC conduit cable
installation, the side wall of the conduit was melted, distorted and blown open,
and the lightning channel had attached to the cable inside and damaged its
insulation. Photographs of the damaged parts of the cables are shown in Fig. 3.
Five fulgurites were found during the excavation of the
underground cables. The excavation process was a slow, methodical one and
covered an area with dimensions of 4 m x 20 m. Various techniques developed in
paleontology were used to remove the fulgurites. The fulgurite excavated over
Cable B was nearly vertical with a length approximately 1 m and an average
diameter of 1.5 cm at the top and about 0.4 cm at the cable. This fulgurite was
the most complete fulgurite excavated as part of the underground power cable
project. It was unearthed in one piece with very little reconstruction
necessary. This fulgurite is presently on exhibit at the Electric Power Research
Institute (EPRI) in Palo Alto, California.
4.2. World-Record Fulgurite (1996)
After the excavation of fulgurites produced as part of the
underground power cable project we started checking for fulgurites at all known
lightning strike points at the Camp Blanding facility. Each year we trigger on
average 30 to 40 discharges some of which strike ground as opposed to
terminating on the rocket launcher. Additionally, the facility receives about 5
lightning strikes that occur naturally, irrespective of our lightning triggering
activity. Our surveillance cameras and observer reports allow us in many cases
to find the strike point on the ground. Such strike points usually appear as
holes in the ground with the surrounding grass being killed (as becomes apparent
within a few days). When the strike point on the ground is found and flagged, it
is impossible to predict if a fulgurite has been created, and, if so, what its
shape and dimensions are. One such find in 1996 led to many days of careful
digging and resulted in the unearthing of a fulgurite having two mostly vertical
branches, one about 16 feet and the other about 17 feet long. It was recognized
by the Guinness Book of Records as the world's longest excavated fulgurite. The
17-foot branch of the world-record fulgurite is shown in Fig. 4. The successful
excavation would not be possible without special tools and the paleontological
skills of Mr. Dan Cordier and Mr. Mike Stapleton. The world-record fulgurite was
carefully separated into sections and covered in plastic material used in
paleontological digs. Each section was measured with special instruments and
labeled for subsequent reassembling. At this time, the world's longest fulgurite
is looking for a home - a museum with sufficient space to display this
magnificent subterranean creation of atmospheric electricity. We have dug up
about ten other fulgurites at Camp Blanding that are on average 4-5 feet long.
In the summer of 1997, researchers at the International
Center for Lightning Research and Testing, Dr. M. A. Uman, Mr. D. J. Cordier,
Mr. K. J. Rambo, and Mr. M. V. Stapleton, worked with Mr. Allan McCollum, an
internationally recognized artist, to create the fulgurite that became the
centerpiece of an artistic installation entitled "Petrified Lightning from
Camp Blanding". The installation was on display at the USF Contemporary Art
Museum in Tampa in Fall 1998 and was accompanied by a simultaneous exhibit and
presentation on the project at the Tampa Museum of Science and Industry (MOSI).
The project was curated and organized by Margaret A. Miller, Director of the USF
Contemporary Art Museum, Jade Dellinger, Independent Curator, and Wit Ostrenko,
Executive Director of MOSI.
The Camp Blanding (fulgurite production) stage of the
project involved the experimentation with minerals of which the fulgurite was to
be made and with various types of containers that were used to avoid the very
difficult excavation process. A fulgurite made of staurolite (75%), ilmenite
(15%), and rutile (10%) is shown, as an example, in Fig. 5. Allan McCollum
selected zircon (ZrSiO4), a heavy mineral that is mined by Du Pont
not far from Camp Blanding, and that is primarily used in the refractory
industry. Zircon melts at 2100-2300° C a melting
temperature which is slightly higher than for silica. Zircon sand was packed in
a 4-foot section of a PVC pipe 6 inches in diameter equipped with two axial
metallic electrodes forming a gap of 15 cm or so in the sand. This container was
placed in a red trash receptacle located near the base of a rocket launcher used
to trigger lightning. Allan McCollum, the artist, helped with the design of the
experiment and was the one to push the rocket-launch button. When lightning was
initiated, lightning current passing through the gap produced a zircon sand
fulgurite resembling a bone. A Florida souvenir factory, Sand Creations,
produced 10,000 replicas of the fulgurite. The replicas were made from a mixture
of zircon (the same mineral from which the original was made) and epoxy. The
artistic installation is shown in Fig. 6. As another element of the installation
Allan McCollum prepared a series of booklets containing more than 50 texts on
fulgurites, lightning and related subjects. The booklets were presented on
tables in a room adjacent to the display of 10,000 replicas of the fulgurite.
Have fun. That is the goal of many of the offerings here at ElectricianEducation.com.
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