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DECODER

VOLCANIC

VOLTAGE

Recent findings shed light on

the intricate processes

behind volcanic lightning.

BY IRENE BERMAN-VAPORIS

AND JASON TREAT

PHOTOGRAPH BY FRANCISCO NEGRONI

When Chile’s Calbuco volcano roared to life in April 2015, it exploded with little warning. The ash-rich plume rose more than 14 miles into the atmosphere, generating a spectacular storm that produced thousands of lightning flashes. Although the tallest and most powerful volcanic explosions tend to produce the most dazzling electrical displays, not all volcanic eruptions trigger lightning. Scientists are just beginning to understand many of the complex processes that determine which ones do. An eruption’s intensity and access to water both play a vital role. Research from recent eruptions in Alaska and Indonesia have clarified how ice can generate lightning, though the precise proportion of ice or ash needed for lightning is unclear. Researchers continue to monitor major eruptions for answers.

HOW VOLCANIC ERUPTIONS

SPARK LIGHTNING

1

Magma breaks up

As magma rises toward the volcano’s surface, its water rapidly turns to vapor, which shatters the molten rock into tiny particles. This creates charged particles during the earliest stage of an eruption.

Rocks

fragment

Gas

expands

Magma reservoir

Near the volcanic vent, tiny electrical discharges emit a signal known as continual radio frequency, an early sign of a volcanic eruption.

2

Particles collide

As the ash plume bursts into the atmosphere, the densely packed particles crash into one another, driven by momentum. Friction makes them gain and lose electrons and become electrically charged.

Volcanic

plume

Collisions between rock particles, a process known as tribocharging, occur when particles scrape or bounce off each other.

3

Charges separate

Positively charged particles begin to separate from negatively charged particles within the plume. This results in a charge imbalance that builds up an electric field strong enough to trigger flashes of lightning.

Particles of

different sizes and charges travel at varying speeds throughout

the entire plume.

4

Water freezes

If a plume rises high enough in the atmosphere, ice will form. Water-rich plumes tend to produce more ice crystals. When ice, hail, and supercooled liquid droplets collide, lightning rates skyrocket.

Ice

Liquid

Vapor

Several miles above this point, water in the plume starts to freeze; this can activate especially intense flashes.

BEHIND THE PHOTOGRAPH

WHERE: Los Lagos, Chile

WHEN: April 2015

The Calbuco volcano erupted in two primary phases in April 2015, exploding for the first time since 1972. The lightning-rich blast was captured in vivid detail by photographer Francisco Negroni.

SOUTH

AMERICA

CHILE

Calbuco

6,611 ft

2,015 m

MAYA WEI-HAAS, SAKKE OVERLUND

SOURCE: ALEXA VAN EATON,

U.S. Geological Survey

VOLCANIC VOLTAGE

Recent findings shed light on the intricate processes

behind volcanic lightning.

BY IRENE BERMAN-VAPORIS AND JASON TREAT

PHOTOGRAPH BY FRANCISCO NEGRONI

When Chile’s Calbuco volcano roared to life in April 2015, it exploded with little warning. The ash-rich plume rose more than 14 miles into the atmosphere, generating a spectacular storm that produced thousands of lightning flashes. Although the tallest and most powerful volcanic explosions tend to produce the most dazzling electrical displays, not all volcanic eruptions trigger lightning. Scientists are just beginning to understand many of the complex processes that determine which ones do. An eruption’s intensity and access to water both play a vital role. Research from recent eruptions in Alaska and Indonesia have clarified how ice can generate lightning, though the precise proportion of ice or ash needed for lightning is unclear. Researchers continue to monitor major eruptions for answers.

HOW VOLCANIC ERUPTIONS SPARK LIGHTNING

1

Magma breaks up

As magma rises toward the volcano’s surface, its water rapidly turns to vapor, which shatters the molten rock into tiny particles. This creates charged particles during the earliest stage of an eruption.

Near the volcanic vent, tiny electrical discharges emit a signal known as continual radio frequency, an early sign of a volcanic eruption.

Rocks

fragment

Gas

expands

Magma reservoir

2

Particles collide

As the ash plume bursts into the atmosphere, the densely packed particles crash into one another, driven by momentum. Friction makes them gain and lose electrons and become electrically charged.

Collisions between rock particles, a process known as tribocharging, occur when particles scrape or bounce off each other.

Volcanic

plume

3

Charges separate

Positively charged particles begin to separate from negatively charged particles within the plume. This results in a charge imbalance that builds up an electric field strong enough to trigger flashes of lightning.

Particles of different sizes and charges travel at varying speeds throughout the entire plume.

4

Water freezes

If a plume rises high enough in the atmosphere, ice will form. Water-rich plumes tend to produce more ice crystals. When ice, hail, and supercooled liquid droplets collide, lightning rates skyrocket.

Several miles above this point, water in the plume starts to freeze; this can activate especially intense flashes.

Ice

Liquid

Vapor

BEHIND THE PHOTOGRAPH

WHERE: Los Lagos, Chile

WHEN: April 2015

SOUTH

AMERICA

The Calbuco volcano erupted in two primary phases in April 2015, exploding for the first time since 1972. The lightning-rich blast was captured in vivid detail by photographer Francisco Negroni.

CHILE

Calbuco

6,611 ft

2,015 m

MAYA WEI-HAAS, SAKKE OVERLUND

SOURCE: ALEXA VAN EATON, U.S. Geological Survey

VOLCANIC VOLTAGE

Recent findings shed light on the intricate processes

behind volcanic lightning.

BY IRENE BERMAN-VAPORIS AND JASON TREAT

PHOTOGRAPH BY FRANCISCO NEGRONI

When Chile’s Calbuco volcano roared to life in April 2015, it exploded with little warning. The ash-rich plume rose more than 14 miles into the atmosphere, generating a spectacular storm that produced thousands of lightning flashes. Although the tallest and most powerful volcanic explosions tend to produce the most dazzling electrical displays, not all volcanic eruptions trigger lightning. Scientists are just beginning to understand many of the complex processes that determine which ones do. An eruption’s intensity and access to water both play a vital role. Research from recent eruptions in Alaska and Indonesia have clarified how ice can generate lightning, though the precise proportion of ice or ash needed for lightning is unclear. Researchers continue to monitor major eruptions for answers.

HOW VOLCANIC ERUPTIONS SPARK LIGHTNING

1

Magma breaks up

As magma rises toward the volcano’s surface, its water rapidly turns to vapor, which shatters the molten rock into tiny particles. This creates charged particles during the earliest stage of an eruption.

Near the volcanic vent, tiny electrical discharges emit a signal known as continual radio frequency, an early sign of a volcanic eruption.

Rocks

fragment

Gas

expands

Magma reservoir

2

Particles collide

As the ash plume bursts into the atmosphere, the densely packed particles crash into one another, driven by momentum. Friction makes them gain and lose electrons and become electrically charged.

Collisions between rock particles, a process known as tribocharging, occur when particles scrape or bounce off each other.

Volcanic

plume

3

Charges separate

Positively charged particles begin to separate from negatively charged particles within the plume. This results in a charge imbalance that builds up an electric field strong enough to trigger flashes of lightning.

Particles of different sizes and charges travel at varying speeds throughout the entire plume.

4

Water freezes

If a plume rises high enough in the atmosphere, ice will form. Water-rich plumes tend to produce more ice crystals. When ice, hail, and supercooled liquid droplets collide, lightning rates skyrocket.

Several miles above this point, water in the plume starts to freeze; this can activate especially intense flashes.

Ice

Liquid

Vapor

BEHIND THE PHOTOGRAPH

WHERE: Los Lagos, Chile

WHEN: April 2015

SOUTH

AMERICA

The Calbuco volcano erupted in two primary phases in April 2015, exploding for the first time since 1972. The lightning-rich blast was captured in vivid detail by photographer Francisco Negroni.

CHILE

Calbuco

6,611 ft

2,015 m

MAYA WEI-HAAS, SAKKE OVERLUND

SOURCE: ALEXA VAN EATON, U.S. Geological Survey