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Volcanic lightning is an electrical discharge caused by a
volcanic eruption A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...
rather than from an ordinary
thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...
. Volcanic lightning arises from colliding, fragmenting particles of
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
(and sometimes
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
), which generate
static electricity Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it can move away by an electric current or electrical discharge. The word "static" is used to differentiate it from electric ...
within the volcanic plume, leading to the name dirty thunderstorm. Moist convection currents and ice formation also drive the eruption plume dynamics and can trigger volcanic lightning. Unlike ordinary thunderstorms, volcanic lightning can also occur when there are no ice crystals in the ash cloud. The earliest recorded observations of volcanic lightning are from
Pliny the Younger Gaius Plinius Caecilius Secundus (born Gaius Caecilius or Gaius Caecilius Cilo; 61 – ), better known in English as Pliny the Younger ( ), was a lawyer, author, and magistrate of Ancient Rome. Pliny's uncle, Pliny the Elder, helped raise and e ...
, describing the eruption of
Mount Vesuvius Mount Vesuvius ( ) is a Somma volcano, somma–stratovolcano located on the Gulf of Naples in Campania, Italy, about east of Naples and a short distance from the shore. It is one of several volcanoes forming the Campanian volcanic arc. Vesuv ...
in 79 AD, "There was a most intense darkness rendered more appalling by the fitful gleam of torches at intervals obscured by the transient blaze of lightning." The first studies of volcanic lightning were also conducted at Mount Vesuvius by Luigi Palmieri who observed the eruptions of 1858, 1861, 1868, and 1872 from the
Vesuvius Observatory The Vesuvius Observatory () is the surveillance centre for monitoring the three volcanic areas of Campania, Italy: Mount Vesuvius, the Phlegrean Fields and Ischia. Founded in 1841 on the slopes of Mount Vesuvius by Ferdinand II of Bourbon, Ki ...
. These eruptions often included lightning activity. Instances have also been reported above Alaska's Mount Augustine volcano, Iceland's
Eyjafjallajökull Eyjafjallajökull (; "glacier of (the mountain) Eyjafjöll"), sometimes referred to by the numeronym E15, is one of the smaller ice caps of Iceland, north of Skógar and west of Mýrdalsjökull. The ice cap covers the caldera of a volcano wi ...
and Grimsvotn,
Mount Etna Mount Etna, or simply Etna ( or ; , or ; ; or ), is an active stratovolcano on the east coast of Sicily, Italy, in the Metropolitan City of Catania, between the cities of Messina, Italy, Messina and Catania. It is located above the Conve ...
in
Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...
,
Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
, Taal Volcano in the
Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...
, Mount Ruang in Indonesia, and Volcán de Fuego in Guatemala.


Charging mechanisms


Ice charging

Ice charging is thought to play an important role in certain types of eruption plumesparticularly those rising above the freezing level or involving magma-water interaction. Ordinary
thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...
s produce lightning through ice charging as water clouds become electrified from colliding ice crystals and other
hydrometeors In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonweal ...
. Volcanic plumes can also carry abundant water. This water is sourced from the magma, vaporized from surrounding sources such as lakes and glaciers, and entrained from ambient air as the plume rises through the atmosphere. One study suggested that the water content of volcanic plumes can be greater than that of thunderstorms. The water is initially transported as a hot
vapor In physics, a vapor (American English) or vapour (Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R ...
, which condenses to
liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...
in the rising column and ultimately freezes to
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
if the plume cools well below freezing. Some eruptions even produce volcanic hail. Support for the ice-charging hypothesis includes the observation that lightning activity greatly increases once volcanic plumes rise above the freezing level, and evidence that ice crystals in the anvil top of the volcanic cloud are effective charge-carriers.


Frictional charging

Triboelectric (frictional) charging within the plume of a volcano during eruption is thought to be a major electrical charging mechanism. Electrical charges are generated when rock fragments, ash, and ice particles in a volcanic plume collide and produce static charges, similar to the way that ice particles collide in regular
thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...
s. The convective activity causing the plume to rise then separates the different charge regions, ultimately causing electrical breakdown.


Fractoemission

Fractoemission is the generation of charge through break-up of rock particles. It may be a significant source of charge near the erupting vent.


Radioactive charging

Although it is thought to have a small effect on the overall charging of volcanic plumes, naturally occurring radioisotopes within ejected rock particles may nevertheless influence particle charging. In a study performed on ash particles from the
Eyjafjallajökull Eyjafjallajökull (; "glacier of (the mountain) Eyjafjöll"), sometimes referred to by the numeronym E15, is one of the smaller ice caps of Iceland, north of Skógar and west of Mýrdalsjökull. The ice cap covers the caldera of a volcano wi ...
and Grímsvötn eruptions, scientists found that both samples possessed a natural radioactivity above the background level, but that radioisotopes were an unlikely source of self-charging in the Eyjafjallajökull plume. However, there was the potential for greater charging near the vent where the particle size is larger. Research continues, and the electrification via radioisotopes, such as
radon Radon is a chemical element; it has symbol Rn and atomic number 86. It is a radioactive noble gas and is colorless and odorless. Of the three naturally occurring radon isotopes, only Rn has a sufficiently long half-life (3.825 days) for it to b ...
, may in some instances be significant and at various magnitudes a somewhat common mechanism.


Plume height

The height of the ash plume appears to be linked with the mechanism which generates the lightning. In taller ash plumes (7–12 km) large concentrations of water vapor may contribute to lightning activity, while smaller ash plumes (1–4 km) appear to gain more of their electric charge from fragmentation of rocks near the vent of the volcano (fractoemission). The atmospheric temperature also plays a role in the formation of lightning. Colder ambient temperatures promote freezing and ice charging inside the plume, thus leading to more electrical activity.


Lightning-induced volcanic spherules

Experimental studies and investigation of volcanic deposits have shown that volcanic lighting creates a by-product known as "lightning-induced volcanic spherules" (LIVS). These tiny glass spherules form during high-temperatures processes such as cloud-to-ground lightning strikes, analogous to fulgurites. The temperature of a bolt of lightning can reach 30,000 °C. When this bolt contacts ash particles within the plume it may do one of two things: (1) completely vaporize the ash particles, or (2) cause them to melt and then quickly solidify as they cool, forming orb shapes. The presence of lightning-induced volcanic spherules may provide geological evidence for volcanic lightning when the lightning itself was not observed directly.


References


External links

*{{commons-inline Severe weather and convection Lightning Electrical phenomena Volcanic eruptions