Glass spheres forged by volcanic lightni ...
Studying volcanic eruptions in person can be dangerous, and scientists have died trying. Volcanic lightning — yes, volcanoes make lightning! — by contrast offers a safer opportunity to examine what happens inside a volcano. But these bright bolts still occur in vicious environments, plus the thick, dense plumes of ash can obscure lightning strikes.
Now, scientists have developed a way to analyze volcanic lightning that is cost effective, relatively simple and safe. Rather than get near volcanic lightning or use expensive equipment, researchers at the Ludwig Maximilian University of Munich in Germany gain clues through a byproduct of the lightning: glass.
Volcanic lightning occurs during an eruption, when hot ash particles rise into the air and rub against each other. The heat and friction create a differential in electric charge that sparks a strike.
The lightning zaps in and out of the thick plumes of rising ash, making the ash so hot it sometimes turns into liquid. If the ash particles are heated sufficiently and given enough time to cool, they can morph into tiny glass spheres — no bigger than a dot from a pen tip. The glass particles then fall back to the ground and gather in large deposits.
“If the lightning event is too short, then the particle won’t melt in the first place,” said Fabian Wadsworth, a University of Munich volcanologist who led the study published in the Journal of Geophysical Research: Solid Earth. But if the heat diffuses into the particle and melts it, then two things happen. With enough time, the melting ash will round into a complete sphere thanks to surface tension. Or if the particle cools at a faster rate than the rounding, the final glass will remain jagged and angular.
Fabian Wadsworth and his team used computer simulations to develop a mathematical model that can predict what eruption conditions were necessary to create the various glass spheres.
The researchers’ model allows them to work backward. By noting a glass particle’s shape, they can determine, the specific lightning conditions of any given eruption. Volcanic lightning strikes vary in temperature and duration. So as a result, the glass particles differ as well.
“The number of lightning events — and how long they last — seems to be somehow related to the distribution of sizes of particles in the plume,” Wadsworth said. “In turn, the distribution sizes of particles in the plume is related directly to how explosive the eruption was that produced them.”
So simulating the conditions under which these glass particles form provides a better understanding of how the volcano erupted.
Volcanic lightning gains steam
“For a long time it was anecdotal, so it’s been interesting to watch that transition develop,” said Stephen McNutt, a volcanologist at the University of South Florida who was not involved in the study. “Now you go to see talks at scientific meetings about volcanoes, and they’re starting to more routinely report lightning.”
In the past, scientists relied on instruments called Lightning Mapping Arrays (LMAs) that detect radio frequencies to resolve the electrical signals from lightning strikes. LMAs, combined with other instruments, allow scientists to create a 3D map of volcanic lightning with an accuracy of within 10 meters, McNutt said. But this technique is expensive and still doesn’t provide all the answers, such as the lightning temperatures.
Wadsworth and his team demonstrated that, using mathematical tools, researchers can back track from big scale natural observations — lightning — to decipher detailed parts of the complicated eruption process. The seemingly small, inconsequential aftermath from the eruptions — glass particles — are akin to a new diagnostic test in a doctor’s office that can clear up portions of the bigger picture.
Plus, this work feeds directly into hazard mitigation for volcanic eruptions. When volcanic ash mixes with rainfall, it creates sludge that can collapse roofs. The traveling ash cloud can cause respiratory problems, damage machinery and stymie renewable energy generation by blocking solar panels. Wadsworth and his team have begun to test if and how well ash particles melted by lightning stick to jet engine surfaces. Knowing this information could guide planes around erupting volcanoes.
The ability to quickly analyze plume conditions, for less cost, will help scientists to foresee potential dangers in the aftermath of an eruption.
“Getting information quickly about the plume conditions helps us predict where plumes will go in certain wind conditions, which obviously helps us prepare for ash arriving in certain parts of the world,” Wadsworth said.
Source - News archive
Researchers quantify the changes that li ...
Benjamin Franklin, founder of the University of Pennsylvania, is believed to have experimented with lightning's powerful properties using a kite and key, likely coming close to electrocuting himself in the process.
In a new set of experiments at Penn, researchers have probed the power of lightning in a less risky but much more technologically advanced fashion.
Chiara Elmi, a postdoctoral researcher in Penn's Department of Earth and Environmental Science in the School of Arts & Sciences, led the work, which used a suite of techniques to examine a fulgurite, a thin layer of glass that forms on the surface of rock when lightning hits it. Among other findings, the study discovered that, based on the crystalline material in the sample, the minimum temperature at which the fulgurite formed was roughly 1,700 degrees Celsius.
"People have been using morphological and chemical approaches to study rock fulgurites, but this was the first time a rock fulgurite was classified from a mineralogical point of view," Elmi said. "I was able to adapt an approach that I've used before to study the effects of meteorite impact in rocks and sediments to analyze a tiny amount of material in order to understand the phase transitions that occur when a lightning hits a rock."
Elmi collaborated on the work with senior author Reto Gieré, professor and chair of the Department of Earth and Environmental Science, along with the department's Jiangzhi Chen, a postdoctoral researcher, and David Goldsby, an associate professor.
Their paper will be published in the journal American Mineralogist.
In a study published last year, Gieré characterized a rock fulgurite found in southern France, finding that the lightning bolt that hit it transformed the layer of rock beneath the fulgurite on the atomic level, producing tell-tale structures called shock lamellae.
The team wanted to pursue a different line of study in the new work.
"In this case," Gieré said, "we instead wanted to study the glass layer in more detail to find out what the minerals present could tell us about the temperature of lightning."
To do so, Elmi performed an X-ray diffraction analysis, which collects information about the way that X-rays interact with crystalline materials to infer the mineral content of a given sample. The challenge in this instance, however, was that a typical X-ray diffraction analysis requires roughly a gram of material, and the quantity of the 10-micrometer thick fulgurite was not nearly that substantial.
To adapt the technique for a smaller quantity of sample, Elmi put the material in a narrow, rotating capillary tube and adjusted the diffraction optics to align, concentrate and direct the X-ray beam toward the sample. The analysis of the fulgurite revealed the presence of glass as well as cristobalite, a mineral with the same chemical composition of quartz but possessing a distinct crystal structure. Cristobalite only forms at very high temperature, and the glass indicated that the top layer of granite melted during the lightning strike. Elmi's analysis enabled her to quantify the glass and the residual minerals in a rock fulgurite for the first time.
"These two signatures indicate a system that received a shock of high temperature," Elmi said. "This analysis also indicates the minimal temperature you have to create the glass because cristobalite forms around 1,700 Celsius, so you know that this temperature was achieved when the lightning hit the rock."
The measured temperature of lightning in the air is in fact much higher—measured at around 30,000 degrees Celsius—but this analysis indicates that the rock itself was raised from ambient temperatures to at least 1,700 Celsius.
The team performed additional analyses on the fulgurite sample. They found organic material in the sample, indicating that the lightning burned lichen or moss growing on the surface of the rock and then trapped it inside the material.
"This is an extremely fast event," Gieré said. "The rock heats up very quickly and also cools down very quickly. That traps gases in the glass and some of these gases were formed by the combustion of organic material."
In future studies, the team hopes to develop a complete model of what happens to rocks during a lightning strike, incorporating chemical, physical, biological and mineralogical observations. They note that people like Franklin who experience near-misses with lightning are lucky indeed.
"It's amazing that a bolt of lightning can turn granite molten and completely change its structure, yet some people survive lightning strikes," said Gieré.
Source - News archive
Upside-down lightning strikes exist and ...
Upward lightning strikes initiate on the ground and head skyward. These discharges, which usually begin at the top of tall and slender structures, pose a real risk for wind turbines. An EPFL study analyzes the mechanisms underlying this poorly understood phenomenon.
Source - Did you know archive
What was that strange light in the sky?
Many people overnight reported seeing strange lights in the sky, a phenomenon that has been reported for centuries before, during, and after earthquakes.
Seismologists aren't in agreement about the causes of the hotly-debated phenomenon - called earthquake lights or, sometimes, earthquake lightning.
And, of course, it's not clear whether the lights overnight in New Zealand were the phenomenon, or something else.
One theory suggests dormant electrical charges in rocks are triggered by the stress of the Earth's crust and plate tectonics, transferring the charge to the surface where it appears as light.
Historical reports include globes, or orbs, of glowing light, floating just above the ground or in the sky.
Much like tidal research, it is an area that is notoriously difficult to investigate. Tidal stresses and their effects on the Earth are minute, but measurable, although many seismologists remain unconvinced by theories of "tidally triggered" earthquakes.
With "earthquake light", the phenomenon is also notoriously difficult to observe, study, and measure.
GNS seismologist Caroline Holden said there were anecdotal reports of lights in the sky.
"Unfortunately, we cannot measure this phenomena or its extent with our instruments to provide a clear explanation," she said.
The phenomenon has been documented for centuries.
Hypotheses have suggested the movement of rocks could generate an electric field, others suggest quakes can lead to rocks conducting electromagnetic energy and a subsequent build up of electric charges in the upper atmosphere.
Yet another theory suggests a link between the electric charge, or current, released by the earth ripping and buckling below the surface, and the magnetic properties of rock.
The charge appears as light, so the theory goes.
People reported similar strange lights in the sky during the 2011 Christchurch earthquake.
In 1888, before a large quake around the Hanmer region, a strange glow in the sky was reported by observers.
One recent study documented hundreds of sightings of strange light, glowing, and aurora-like reports, from 1600 to the 19th century.
The study in the Seismological Research Letters suggested a charge builds up in rock inside the Earth's crust and, as it becomes rapidly unstable in a quake, expands outward.
In an earthquake, the electrical charge transfers from below the surface to the surface, or above, depending on the conductivity of the rock - appearing as light.
"When such an intense charge state reaches the Earth's surface and crosses the ground–air interface, it is expected to cause [an electric transmission and breakdown] of the air and, hence, an outburst of light.
"This process is suspected to be responsible for flashes of light coming out of the ground and expanding to considerable heights at the time when seismic waves from a large earthquake pass by."
The study said some seismologists also think the theory could account for other phenomena, such as changes to electrical fields, strange fog, haze, clouds, and low-frequency humming or radio frequency emission.
In the study, the researchers found the light was more often associated with a type of quake in which tectonic plates are wrenched apart, known as a "rift" earthquake
Source - Did you know archive
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