Volcanic lightning has very little to do with tectonic activity, and everything to do with everyday physics.
 
Volcanic lightning is not formed deep in the Earth. It only forms in a volcanic plume, the cylinder-shaped column of volcanic ash emitted by some erupting volcanoes. Volcanoes that lack a thick volcanic plume usually lack volcanic lightning. Volcanoes in Hawaii, for instance, are more likely to eject fluid lava fountains than thick plumes of ash. These volcanoes rarely have volcanic lightning.
 
The tiny particles that make up a volcanic plume are tightly compressed beneath a volcano. The airy atmosphere aboveground, however, is much less dense. This change in density contributes to volcanic lightning.
 
As densely packed particles are violently ejected in a volcanic plume, they rub against each other. This interaction is called friction. Through friction, ash particles gain and lose electrons—they become electrically charged. As charged particles ascend the less-dense volcanic plume, the plume experiences charge separation. Positively charged particles become increasingly separated from negatively charged particles.
 
When the charge separation becomes too great for air to resist the flow of electricity, lightning tears through the volcanic plume to connect the positively and negatively charged particles.
 
Everyday Lightning
 
You don’t need an actual volcano to get an idea of how volcanic lightning works. Friction creates charged particles when you rub a balloon across your hair or your socked feet across a carpet. You’re covering the balloon or yourself with negative particles. This imbalance of electrons is called static electricity.
 
Eventually, you come into contact with something—another person or a metal doorknob, for instance—that is not electrically charged. The static “shock” you receive is the lightning-fast discharge of electrons.

  1. Volcanic lightning is most often reported at night. Why do you think people are more likely to report seeing volcanic lightning at night than during the day?

    • Answer

      Volcanic lightning is most likely to appear at the beginning of an eruption, no matter what time of day that happens.

      People are more likely to see volcanic lightning at night, however. Volcanic lightning may crackle during daytime eruptions, but is more likely to be lost in the sun’s glare.

  2. Lightning from thunderclouds can appear as bolts, sheets, or balls. What shapes do you think volcanic lightning can take?

    • Answer

      All of the above! During the 1980 eruption of Mount St. Helens, Washington, for instance, the thick volcanic plume produced bolts of lightning connecting to the ground, sheet lightning connecting in the plume itself, and ball lightning bouncing near the volcano.

  3. A common nickname for the conditions that support volcanic lightning is a “dirty thunderstorm.” What makes this thunderstorm “dirty”?

    • Answer

      The “dirt” is the thick ash and rock of the volcanic plume.

ascend
Verb

to go up.
atmosphere
Noun

layers of gases surrounding a planet or other celestial body.
charge separation
Noun

building of space between charged particles. Sometimes called static electricity.
compress
Verb

to press together in a smaller space.
cylinder
Noun

tube or long, circular object.
dense
Adjective

having parts or molecules that are packed closely together.
discharge
Verb

to eject or get rid of.
eject
Verb

to get rid of or throw out.
electricity
Noun

set of physical phenomena associated with the presence and flow of electric charge.
electron
Noun

negatively charged subatomic particle.
emit
Verb

to give off or send out.
erupt
Verb

to explode or suddenly eject material.
fluid
Noun

material that is able to flow and change shape.
friction
Noun

force produced by rubbing one thing against another.
lava fountain
Noun

phenomenon where lava is forcefully but not violently ejected from a volcano through a fissure or vent.
particle
Noun

small piece of material.
physics
Noun

study of the physical processes of the universe, especially the interaction of matter and energy.
static electricity
Noun

motionless electronic charge that builds up on a material.
tectonic activity
Noun

movement of tectonic plates resulting in geologic activity such as volcanic eruptions and earthquakes.
violent
Noun

strong, destructive force.
volcanic ash
Noun

fragments of lava less than 2 millimeters across.
volcanic lightning
Noun

bolts of electricity produced in a volcanic plume. Also called a dirty thunderstorm.
volcanic plume
Noun

cylinder-shaped structure of volcanic ash and gas emitted by an explosive volcanic eruption. Also called an eruption column.
volcano
Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

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    Writer

    Caryl-Sue, National Geographic Society

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    Melissa MacPhee, National Geographic Society

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    Caryl-Sue, National Geographic Society

    Last Updated

    Oct. 28, 2015

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