So far in this series, we’ve talked about man-made byproducts — Fordite, which is built-up layers of cured car enamel, and Trinitite, which was created during the first nuclear bomb test.

But not all byproducts are man-made, and not all of them are basically untouchable. Some are created by Mother Nature, but are nonetheless dangerous. I’m talking about fulgurites, which can form whenever lightning discharges into the Earth.

It’s likely that even if you’ve seen a fulgurite, you likely had no idea what it was. So what are they, exactly? Basically, they are natural tubes of glass that are formed by a fusion of silica sand or rock during a lightning strike.

Much like Lichtenberg figures appear across wood, the resulting shape mimics the path of the lightning bolt as it discharged into the ground. And yes, people make jewelry out of fulgurites.

Lightning Striking Again

Lightning is among the oldest observed phenomena on Earth. You probably know that lightning is just a giant spark of electricity in the atmosphere. It can occur between clouds, the air, or the ground and often hits tall things like skyscrapers and mountaintops.

Lightning is often visible during volcanic eruptions, intense forest fires, heavy snowstorms, surface nuclear detonations, and of course, thunderstorms.

In lightning’s infancy, air acts as an insulator between charges — the positive and negative charges between the cloud and the ground. Once the charges have sufficiently built up, the air’s insulating qualities break down and the electricity is rapidly discharged in the form of lightning.

When lightning strikes, the energy in the channel briefly heats up the air to about 50,000 °F, which is several times the surface of the Sun. This makes the air explode outward. As the shock wave’s pressure decreases, we hear thunder.

Of Sand and Rock and Other Stuff

Fulgurites, also known as fossilized lightning, don’t have a fixed composition: they are composed of whatever they’re composed of at the time of the lightning strike. Four main types of fulgurites are officially recognized: sand, soil, caliche (calcium-rich), and  rock fulgurites. Sand fulgurites can usually be found on beaches or in deserts where clean sand devoid of silt and clay dominates. And like those Lichtenberg figures, sand fulgurites tend to look like branches of tubes. They have rough surfaces comprised of partially-melted grains of sand.

When sand fulgurites are formed, the sand rapidly cools and solidifies. Because of this, they tend to take on a glassy interior. As you might imagine, the size and shape of a fulgurite depends on several factors, including the strength of the strike and the depth of the sand being struck. On average, they are 2.5 to 5 cm in diameter, but have been found to exceed 20 cm.

Soil fulgurites can form in a wide variety of sediment compositions including clay-, silt-, and gravel-rich soils as well as leosses, which are wind-blown formations of accumulated dust. These also appear as tubaceous or branching formations, vesicular, irregular, or a combination thereof.

Calcium-rich sediment fulgurites have thick walls and variable shapes, although it’s common for multiple narrow channels to appear. These can run the gamut of morphological and structural variation for objects that can be classified as fulgurites.

Rock fulgurites are typically found on mountain peaks, which act as natural lightning rods. They appear as coatings or crusts of glass formed on rocks, either found as branching channels on the surface, or as lining in pre-existing fractures in the rock. They are most often found at the summit or within several feet of it.

Fact-Finding Fulgurites

Aside from jewelry and such, fulgurites’ appeal comes in wherever they’re found, as their presence can be used to estimate the number of lightning strikes in an area over time.

Then again there’s some stuff you may not necessarily want to use in jewelry making. Stuff that can be found in the dark, dank corners of the Earth. Stay tuned!

Mark it on your calendars, folks — this is the week that the term RUD has entered the public lexicon. Sure, most of our community already knows the acronym for “rapid unscheduled disassembly,” and realizes its tongue-in-cheek nature. But given that the term has been used by Elon Musk and others to describe the ignominious end of the recent Starship test flight, it seems like RUD will catch on in the popular press. But while everyone’s attention was focused on the spectacular results of manually activating Starship’s flight termination system to end its by-then uncontrolled flight at a mere 39 km, perhaps the more interesting results of the launch were being seen in and around the launch pad on Boca Chica. That’s where a couple of hundred tons of pulverized reinforced concrete rained down, turned to slag and dust by the 33 Raptor engines on the booster. A hapless Dodge Caravan seemed to catch the worst of the collateral damage, but the real wrath of those engines was focused on the Orbital Launch Mount, which now has a huge crater under it.

So how close to space did Starship actually make it? Not even close, if your standard is the 100-km Kármán Line. If you want to visualize just how far that’s not, check out this fun little Space Elevator page. You start at ground level on Earth and scroll ever upward, with the different layers of the atmosphere being called out along with the altitudes of various aircraft and spacecraft — and meatcraft too, like Felix “Free Fallin'” Baumgartner’s famous sound barrier-breaking skydive, or the ridiculous bar-headed goose, which routinely flies in the rarified air above the Himalaya mountains honking loudly the whole time. This a space elevator, elevator music is kindly provided, although we were disappointed that it wasn’t “The Girl from Ipanema.”

A little closer to the ground, we ran across a spectacular bit of footage that shows just how lightning rods work. Physicists in Brazil set up a high-speed camera and managed to catch an aerial lightning bolt in the act of seeking out a leader from the ground, or rather from the roof of a tall building. The leader was one of just many stretching up from various charge-concentrating points on the ground, and it wasn’t clear which one of the leaders was going to “win” the race to complete the circuit. Watching the aerial bolt seeking the path of least resistance is fascinating, and hats off to the researchers for capturing these images.

This week on the podcast we talked about using an analog oscilloscope in X-Y mode as a vector graphics display. That had us pining for an analog scope of our own to play with, and while we’ve got a Tektronix 475, it’s a bit disassembled at the moment. Until we get that back together again, we’ll settle for this online oscilloscope that lets you play with things like Lissajous patterns. The scope’s “tube” is very convincing, and you can control both the persistence and color of the phosphor. You can use the virtual signal generator to pipe different functions to each input, throw audio from your microphone into the signal, control the trigger and timebase, and generally do all the fun things an oscilloscope can do.

And finally, for your viewing pleasure this weekend, we present some crazy engineering from the 1960s. The LeTourneau TC-497 “Land Train” was an attempt by the US Army to go where no road had gone before, particularly in arctic conditions — think “Cold War.” Ironically, the last surviving bit of Land Train hardware now lives in the desert, at the Yuma Proving Grounds in Arizona. The TC-497, which as the lead car in the train acted sort of like a locomotive in a traditional train, has been lovingly restored to its 1960s glory — without the nuclear reactor that could have powered it — when crews lived and worked aboard her. It’s an amazing bit of engineering history that you should check out.

Few things are more impressive than a lighting strike. Lightning can carry millions of volts and while it can be amazing to watch, it is somewhat less amazing to be hit by lightning. Rockets and antennas often have complex lightning protection systems to try to coax the electricity to avoid striking where you don’t want it. However, a European consortium has announced they’ve used a very strong laser to redirect lightning in Switzerland. You can see a video below, but you might want to turn on the English closed captions.

Lightning accounts for as many as 24,000 deaths a year worldwide and untold amounts of property and equipment damage. Traditionally, your best bet for protection was not to be the tallest thing around. If the tallest thing around is a pointy metal rod in the ground, that’s even better. But this new technique could guide lightning to a specific ground point to have it avoid causing problems. Since lightning rods protect a circular area roughly the radius of their height, having a laser that can redirect beams to the area of a lightning rod would allow shorter rods to protect larger areas.

The idea is simple. Electricity follows a path of least resistance. When electric charges are high enough to cause the air to ionize, that creates lightning. However, if a laser ionizes the air preemptively, the lightning will be prone to follow that path instead of creating a new one.

You won’t be able to replicate this with your favorite laser pointer. The laser used is a 1 kW laser that puts out a one picosecond pulse. A Swiss radio tower at a height of over 2.5 km was monitored for lightning strikes both with and without the laser system. The increased protection was modest, only 60 meters more than the lightning rod alone. However, the team wants to shoot for a 500-meter increase.

We don’t know if this will be super practical for most lightning protection jobs. We doubt that even [styropyro’s] laser is up to the task. If you want more background on the natural phenomena, [Maya Posch] took us through it last year.

Lightning is one of the more mysterious and fascinating phenomenon on the planet. Extremely powerful, but each strike on average only has enough energy to power an incandescent bulb for an hour. The exact mechanism that starts a lightning strike is still not well understood. Yet it happens 45 times per second somewhere on the planet. While we may not gain a deeper scientific appreciation of lightning anytime soon, but we can capture it in various photography thanks to this project which leverages computer vision machine learning to pull out the best frames of lightning.

The project’s creator, [Liam], built this as a tool for stormchasers and photographers so that they can film large amounts of time and not have to go back through their footage manually to pull out the frames with lightning strikes. The project borrows from a similar project, but this one adds Python 3 capabilities and runs on a tiny netbook for more easy field deployment. It uses OpenCV for object recognition, using video files as the source data, and features different modes to recognize different types of lightning.

The software is free and open source, and releases are supported for both Windows and Linux. So far, [Liam] has been able to capture all kinds of electrical atmospheric phenomenon with it including lightning, red sprites, and elves. We don’t see too many projects involving lightning around here, partly because humans can only generate a fraction of the voltage potential needed for the average lightning strike.

Along with many other natural phenomena, lightning is probably familiar to most. Between its intense noise and visuals, there is also very little disagreement that getting hit by a lightning strike is a bad thing, regardless of whether you’re a fleshy human, moisture-filled plant, or conductive machine. So it’s more than a little bit strange that the underlying cause of lightning, and what makes certain clouds produce these intense voltages along ionized air molecules, is still an open scientific question.

Many of us have probably learned at some point the most popular theory about how lightning forms, namely that lightning is caused by ice particles in clouds. These ice particles interact to build up a charge, much like in a capacitor. The only issue with this theory is that this process alone will not build up a potential large enough to ionize the air between said clouds and the ground and cause the lightning strike, leaving this theory in tatters.

A recent study, using data from Earth-based radio telescopes, may now have provided fascinating details on lightning formation, and how the charge may build up sufficiently to make us Earth-based critters scurry away to safety when dark clouds draw near.

Follow The Streamers

The most succinct way to summarize lightning is probably as a ‘really big spark’. Like any spark, this requires the build up of a potential to the point where the dielectric medium between the potential and a target breaks down. In the case of air as the dielectric medium, this involves the breaking down of air molecules, at roughly 2 MV/m, into electrically conductive plasma by stripping electrons from atoms. Once there is a plasma track, the rest of the charge is free to dump; during the subsequent discharge in a lightning strike, in the order of a gigajoule of energy is transferred.

To build up this charge, the triboelectric effect is deemed to be primarily involved. While heavier graupel (soft hail) remains mostly stationary inside the cloud, updrafts carry lighter ice crystals and super-cooled droplets between the graupel, resulting in the physical interaction that underlies the triboelectric charging effect.

As noted earlier, the resulting charge that builds up inside a thundercloud in this manner is not sufficient by itself to cause a lightning stream with the ground. This has for ages left open the question of what initiates the build-up of such a breakdown. One theory here is that of relativistic runaway electron avalanche (RREA), with an extensive explanation provided by Gurevich et al. (2005) in Physics Today (PDF).

The short version of this theory is that relativistic electrons from outside the atmosphere are the trigger for the sudden initiation charge of a lightning strike event. As the electrons that exist inside the cloud at that point are thermal (‘slow’) electrons, this would provide the impulse that would set off the formation of self-replicating streamers.

Streamers are the clearest observable sign of a lightning strike in progress: they are ionization events caused by the breakdown of the air molecules into a plasma. This does not only provide an electrical path for the stored charge, but also causes the release of electromagnetic radiation. If there are enough free electrons to continue the further ionization of the surrounding air, the streamer will propagate, with ultimately a leader surge forming.

It is this leader that forms the clear bright line in a lightning strike, preceded and surrounded by streamers.

Lit Up Like A Christmas Tree

If there’s one property of clouds that makes them a bother when it comes to observing the formation of lightning, it is that they are opaque to most types of observations. Whether we send up balloons with cameras, fly airplanes around or through thunderstorms, the problem remains that we cannot see a lot of what’s happening inside the clouds. The main exception to this is in the RF spectrum, which is where thunderstorms are exceptionally visible.

As mentioned by Gurevich et al., during thunderstorms RF events called narrow bipolar pulses of about 5 μs are common, along with X-ray bursts that can last up to a minute. These events are in addition to the release of gamma ray bursts (0.05 MeV – 10 MeV) that occur at an altitude of between 500 and 600 km. For Gurevich et al. these highly energetic events were highly indicative of relativistic electrons playing a role in lightning ignition.

Due to the aforementioned difficulties with actually seeing inside clouds, all of this was based on observations in mostly the radio spectrum, until a 2018 attempt by the Dutch Low-Frequency Array (LOFAR) radio telescope was it possible to image the formation of a lightning strike in 3D space. As implied by the name, LOFAR consists out of an array of distributed radio telescopes, with a core in the Netherlands and further distributed throughout Europe.

Using the Dutch part of the array, it was possible to use the time-delay from the observed RF events during a lightning storm at the different parts of the array to form a picture of the events as they developed. This enabled Sterpka et al. to create the following hypothesis based on these observations.

What they found is that, rather than an external trigger, the process starts (a) with a single positive streamer (b), which creates the initial VHF field (c). The middle panel describes an avalanche cascade of streamers, with each streamer producing more streamers, creating the ever stronger VHF field, which the LOFAR equipment captured. Finally, the right panel shows the formation of a leader (h).

Sterpke et al. propose that the narrow bipolar pulses that are observed at the initialization event are due to the breakdown of virgin air or similar, which forms a precondition for the lightning initiation. Perhaps the most interesting finding is that a system of streamers appear to have very different properties from an individual streamer, which might play a significant role in the formation of lightning.

Flashy Science

Interestingly, lightning is a phenomenon that doesn’t just affect the present, but also the past. When lightning strikes the ground, it can cause the formation of fulgurites (from Latin fulgur, meaning ‘lightning’). This is a type of mineraloid formed by the fusion of mineral grains, which follows the shape of the lightning strike which was responsible for its formation. Within a lightning channel, temperatures can exceed 30,000 Kelvin.

More than just a curiosity, fulgurites are an invaluable paleoenvironmental indicator, giving us an idea of what the climate including lightning frequency was like in a region. This is part of the field of paleolightning. Along with evidence of the role lightning may have played during the formation of life on Earth (e.g. the Miller-Urey experiment), lightning plays a role in nitrogen fixation.

Another interesting, more recent finding came from during the SARS-CoV-2 pandemic and the shutdowns of 2020. Namely that of the correlation between pollution and the frequency of lightning. This would presumably be due to anthropogenic pollution providing e.g. fine dust particles which form a nucleus for ice formation inside clouds.

Hopefully over the coming years we’ll find out more details about what makes lightning work, as well as what affects the formation of the cumulonimbus clouds. With more refined radio telescope arrays like the Square Kilometre Array (SKA) coming online, it might be that they could give us more glimpses at this phenomenon that has mesmerized human cultures since the dawn of time.

While being an obvious risk to life and property, lightning remains one of the primal forces that shaped the biosphere of the Earth, and continues to do so to this day. Even as we admire its beauty from a (hopefully) safe distance, it might behoove us to acknowledge how little we truly know about it and the high-energy physics that underlie it.

Lightning is a force to be reckoned with: ever since ancient times, humans have been in awe of the lethal power of lightning strikes and the deafening roar of thunder. Quite reasonably, they ascribed these events to acts of angry gods; today, modern science provides a more down-to-earth explanation of the physics involved, and a world-wide network of sensors generates a real-time record of lightning strikes around the globe.

[Dmitry Morozov]’s latest kinetic art installation called Adad is driven by this stream of data. Named after a Mesopotamian god of thunder, it consists of a set of arms that suddenly jerk upwards when a lightning strike is detected anywhere in the world. When an arm falls down again, it strikes a piezo crystal, which generates an electric charge that triggers a bright flash of light as well as a sound effect. Those crystals are pieces of potassium sodium tartrate (also known as Rochelle salt) and were grown specifically for this project. They are housed in plexiglass holders which also provide electrical connections.

Adad‘s spider-like design, its eerie sounds as well as the sudden pops and flashes make this a rather unsettling yet beautiful display of Nature’s violence. And it’s a piece of beauty from an engineering point of view as well: sleek aluminium tubes, servo-driven motion and those transparent crystal holders, all controlled by an Arduino that receives live lightning data through an internet connection.

We’ve seen several types of lightning detectors, usually based on a standard radio receiver or a specialized chip. If you’re interested in growing your own piezo crystals, we’ve covered that too.

Apple iPhones ship with the company’s Lightning cable, a capable and robust connector, but one that’s not cheap and is only useful for the company’s products. When the competition had only micro-USB it might have made sense, but now that basically all new non-fruity phones ship with USB-C, that’s probably the right way to go.

[Ken Pilonell] has addressed this by modifying his iPhone to sport a USB connector. The blog post and the first video below the break show us the proof of concept, but an update in the works and a teaser video show that he made it.

We’re a bit hazy on the individual iPhone model involves, but the essence of the work involves taking the internals of a Lightning-to-USB-C cable and hooking it up to the phone’s internal Lightning port. The proof-of-concept does it by putting the Apple flexible PCB outside the phone and plugging the cable part in directly, but it seems his final work involves a custom flexible board on which the reverse-engineered USB-C converter parts are mounted along with the USB-C socket itself. We see a glimpse of machining the slot in the phone’s case to USB-C dimensions, and we can’t wait for the full second installment.

It’s purely coincidental, but this comes against a backdrop of the European Union preparing to mandate USB-C on all applicable devices.

Thanks [Itay] for the tip!