On the night of January 15, 2022, satellites orbiting above the South Pacific picked up something that made veteran atmospheric scientists stop and stare. An expanding ring of lightning was spreading outward from a submerged volcano in Tonga. At its peak, the storm above Hunga volcano fired more than 2,600 flashes per minute. For comparison, the most intense thunderstorms people had measured before that topped out under 1,000.
Volcanic lightning isn’t new, though. People have been writing about it for about two thousand years. What’s new is that we finally have the instruments to study it properly, and the picture that’s emerging is stranger and more useful than anyone expected.
So why do some volcanoes produce lightning while others, even large ones, stay dark? Let’s work through it.
What volcanic lightning actually is
Volcanic lightning is an electrical discharge that happens in or around an eruption plume. Mechanically, it’s the same basic thing as the lightning in a summer storm: a buildup of electric charge in one region, an opposite charge somewhere nearby, and eventually a breakdown of the air between them in a bright, hot spark.
The difference is where it happens and what’s carrying the charge. In an ordinary thunderstorm, the actors are water droplets, ice crystals, and hail. In an eruption, they’re ash, rock fragments, gas, and, depending on conditions, ice as well.
Scientists sometimes call an eruption column a “dirty thunderstorm,” and the nickname is fairly accurate. The U.S. Geological Survey’s Volcano Science Center has described how plumes can develop thunderstorm-style electrification once they climb high enough, but eruptions also have electrical tricks of their own that ordinary storms don’t.
Where the charge comes from
There isn’t one single answer, and that’s part of why the topic remains an active research area. Researchers point to a few overlapping mechanisms.
1. Fragmentation and fracture
Magma isn’t gentle when it erupts. As gas-charged magma rips itself apart, it shatters into fragments of every size, from boulders down to dust finer than flour. Breaking solid material separates electric charge, a process researchers call fractoemission. Fresh surfaces carry charge, and billions of freshly made fragments start the plume’s electrical life already loaded.
2. Particle collisions (triboelectric charging)
Once the ash is airborne, it doesn’t just drift. It’s thrown around in a violent, turbulent jet, and particles smash into each other constantly. Different-sized particles tend to pick up opposite charges when they collide, the same way rubbing a balloon on your hair leaves it charged. Smaller grains often end up with one sign and larger ones with the other. Then gravity and the plume’s own motion sort them apart, with light grains rising and heavy ones dropping out. You end up with a big separation of charge, which is exactly what lightning needs.
3. Ice charging in the upper plume
This is the thunderstorm connection. Volcanic plumes carry huge amounts of water vapor, some from the magma itself and more from air and (in some cases) seawater or melting glaciers. When the plume rises high enough that temperatures fall well below freezing, that water turns into ice. Then you have ice crystals and graupel colliding in a turbulent updraft, which is the classic recipe for charging in ordinary storm clouds.
USGS researchers studying Alaska’s Bogoslof volcano found strong evidence for this. Sensors recorded more than 4,550 volcanic lightning strokes over nine months of eruptions, yet only 32 of the 70 explosive events produced detectable lightning. The pattern was telling: lightning didn’t start until plumes climbed above the freezing level, roughly the height where temperatures hit minus 20°C. When the plume stayed low, there was no lightning. When it reached the cold zone and ice formed, the flashes began.
Two phases of lightning in one eruption
If you watch a long eruption closely, you’ll notice the lightning isn’t uniform. Scientists generally describe two broad phases, as EarthSky’s explainer lays out.
Near-vent (eruptive) lightning. This appears right at the start, within seconds of the blast and close to the crater. It’s usually short, small-scale, and sparking constantly, a crackle of flashes in the roaring gas jet just above the vent. This is mostly driven by the fragmentation and collision processes above, because the material is fresh, fine-grained, and moving violently.
Plume lightning. This shows up later, as the cloud rises and spreads downwind. It tends to be bigger, with longer flashes reaching through the developing column. Here, ice and large-scale charge separation matter most, and that’s why plume lightning looks more like a thunderstorm’s.
The USGS Bogoslof paper actually breaks the near-vent end into finer categories, including tiny “vent discharges” that occur within meters of the opening, but the two-phase framing is the easiest way to picture an eruption’s electrical evolution.
So why do only some volcanoes do it?
If lightning needs just ash, collisions, and a cloud, you’d expect every explosive eruption to produce it. Yet plenty don’t. A few factors decide it.
The eruption has to be explosive. Quiet, oozing lava flows, like most of what Hawaii’s Kīlauea produces in effusive phases, make no lightning. You need violent fragmentation. That pushes lightning toward volcanoes with sticky, gas-rich magma, though basaltic eruptions can also do it if they’re explosive enough.
Fine ash matters. Fine particles carry the most charge relative to their mass, and a plume rich in very fine grains has more charge to separate. Eruptions that produce coarse material and little dust are electrically duller.
Plume height and temperature matter. The Bogoslof results make this clear. A plume that stays below the freezing level can still make some near-vent lightning, but the big plume-scale discharges seem to need ice. Cold-climate volcanoes, or those that blast ash very high, have an advantage.
Water makes a difference. Water is the key ingredient in making ice. Eruptions through glaciers, crater lakes, or shallow seas inject extra moisture and can supercharge a plume. That’s the leading explanation for Hunga, a shallow submarine volcano that threw seawater and steam into an already enormous plume.
Magnitude and intensity count. Bigger, more vigorous eruptions loft more material faster, which means more collisions, more charge, and more flashes. Lightning is often more common and more intense in large eruptions.
Put differently, lightning is the product of a stack of conditions lining up. That’s why two eruptions of similar size can behave so differently.
Famous cases
A handful of eruptions have given researchers rich lightning data.
Vesuvius, 79 CE and later. The Roman writer Pliny the Younger described flashes in the dark column rising over Vesuvius in his famous letters about the eruption that buried Pompeii. In the 19th century, the Italian physicist Luigi Palmieri, working from the Vesuvius Observatory, made some of the earliest scientific observations of electrical activity during eruptions in the 1800s.
Eyjafjallajökull, Iceland, 2010. This eruption famously grounded European air traffic, and it also produced gorgeous, widely photographed lightning above the glacier-covered vent. Meltwater and ice interacting with magma likely helped the electrical show.
Chaitén, Chile, 2008. Chaitén erupted with little warning and generated plenty of lightning in a plume that was photographed extensively, giving researchers a good record of the phenomenon.
Sakurajima, Japan. One of the most active volcanoes on Earth, Sakurajima erupts so often that scientists can set up instruments and wait. Research there, using high-speed cameras and electromagnetic sensors, found that volcanic lightning typically occurs in the lower part of the developing plume, within a few hundred meters of the crater, and that flash counts relate to how much ash is released. That second finding is exciting because it suggests lightning could one day serve as a quick gauge of eruption size.
Bogoslof, Alaska, 2016–2017. As covered above, this submarine-to-island volcano gave scientists a long run of eruptions to compare, which is how they tied lightning to the freezing level.
Hunga, Tonga, 2022. The record-holder, and worth a closer look.
The Hunga eruption: lightning on a different scale
The Hunga eruption was one of the largest explosive events ever captured by modern instruments. A team led by USGS scientist Alexa Van Eaton combined four different sources of lightning data. According to the American Geophysical Union’s announcement of the study in Geophysical Research Letters, the eruption produced just over 192,000 flashes, peaking at 2,615 flashes per minute. It also produced the highest-altitude lightning ever measured, at 20 to 30 kilometers above sea level.
The flashes organized themselves into concentric rings expanding and contracting around the vent, a pattern the team hadn’t expected. As Van Eaton put it, the scale of the rings blew their minds.
Why so much? The leading explanation is the volcano’s setting. The eruption was submarine, so enormous amounts of seawater met hot magma, flashing to steam and rocketing into the atmosphere. That created a moisture-loaded plume that punched far above the freezing level, a near-perfect environment for ice charging at a scale no ordinary storm could match.
There was a practical payoff too. The towering plume hid the vent from satellites, so the lightning became a window into what was happening inside. The researchers used the flash data to show that the eruption lasted much longer than the hour or two first observed and went through multiple phases. You can read the USGS summary of the findings for more detail.
Can volcanic lightning leave a trace?
Yes, and it’s one of the odder discoveries in the field. When a lightning bolt passes through a cloud of ash, the extreme heat can melt tiny grains, which then cool into little glass beads called lightning-induced volcanic spherules, or LIVS. Researchers at the University of Alabama reported finding these in ash deposits, and they matter because they can serve as geological evidence that lightning occurred, even in eruptions nobody saw. That could help volcanologists reconstruct the electrical history of ancient eruptions from the rocks alone.
Why this research matters beyond the spectacle
It would be easy to treat volcanic lightning as just a beautiful curiosity. It’s actually becoming a working tool.
Monitoring remote volcanoes. Many volcanoes sit in remote areas, such as the Aleutian arc in Alaska, where there’s little ground instrumentation. Global lightning detection networks can pick up the radio signals of flashes thousands of kilometers away. At Bogoslof, lightning helped confirm ash-producing explosions in near real time, even when weather or darkness blocked the view.
Aviation safety. Ash is a serious hazard for jet engines. If lightning tracks plume activity, forecasters can use it to flag when and where ash is being injected into flight routes. This is among the biggest reasons agencies are interested in the work.
Estimating eruption size and timing. If flash rates correlate with ash output, as the Sakurajima results hint, lightning could provide a fast first estimate of how big an eruption is, before satellite imagery or ground reports come in.
Understanding plume physics. Electrical measurements reveal how particles move and interact inside a plume, something that’s hard to see directly. That can improve the models used to predict where ash goes.
For authoritative background on how scientists track and classify volcanic activity worldwide, the Smithsonian Institution’s Global Volcanism Program maintains a searchable record of eruptions and reports.
What we still don’t know
Honesty matters here, because the field is still young. Volcanic lightning has been captured in detail only at a limited number of eruptions, partly because volcanoes are remote, eruptions are unpredictable, and dense ash clouds can hide the flashes you’re trying to measure. The relative weight of fragmentation charging, particle collisions, and ice charging likely varies from one eruption to the next, and researchers are still sorting out how much each contributes under different conditions.
There are open questions about those Hunga lightning rings, about how common such extreme events might be in the geological past, and about whether lightning could ever be reliable enough to anchor an official warning system rather than just supplement one. Expect those answers to sharpen as sensors improve and the next big eruption gives scientists fresh data.
The takeaway
Volcanic lightning happens when an eruption does the same thing a thunderstorm does, only faster and more violently. Rock shatters, ash collides, ice forms in the cold upper plume, and the resulting charge separation breaks down in a flash. Whether a particular volcano produces it depends on how explosive the eruption is, how fine the ash is, how high the plume climbs, and how much water is involved.
The most exciting part is that this isn’t just a pretty show. Every flash is a signal, one that helps scientists see inside clouds they can’t otherwise look through, track dangerous ash, and understand the planet’s most violent weather. The next time you see a photo of a night eruption laced with bolts, you’re looking at physics researchers are still learning to read.
