Volcanic Lightning

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?
  
  Show 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?
  
  Show 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”?
  
  Show Answer
  
  The “dirt” is the thick ash and rock of the volcanic plume.
Articles & Profiles
Images
- National Geographic News: Volcanic Lightning Illuminated

Term	Part of Speech	Definition	Encyclopedic Entry
ascend	Verb	to go up.
atmosphere	Noun	layers of gases surrounding a planet or other celestial body.	Encyclopedic Entry: atmosphere
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.	Encyclopedic Entry: Human and Environmental Impacts of Volcanic Ash
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.	Encyclopedic Entry: Plate Tectonics and Volcanic Activity

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Writer

Caryl-Sue, National Geographic Society

Editor

Melissa MacPhee, National Geographic Society

Producer

Caryl-Sue, National Geographic Society

Last Updated

Oct. 28, 2015

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