Lightning in the Volcanic Plume
Lightning is frequently observed in the eruption columns of large volcanoes, but it is rare in Hawaiian eruptions. For one week in July 2008, when the ocean entry produced an especially large and vigorous plume, lightning was seen repeatedly.
Frequently Asked Questions
Why is there lightning in the eruption cloud?
Lightning is one of nature’s most fascinating spectacles, and one of the most complicated: scientists still don’t understand it fully. Below is a simplified explanation.
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Friction between certain materials creates a charge separation because some materials have a stronger “attraction” for electrons than others. When two of these materials (for example, a balloon and a wool sweater) are brushed against one another, an excess of electrons accumulates on one surface and a deficiency of electrons on the other surface. In a dry climate, rubbing your leather-soled shoes on a polyester carpet as you walk can result in a spark as you reach for the doorknob; pulling apart synthetic garments fresh from the dryer frequently produces a spark.
In a thunderstorm, high winds cause the ice particles in clouds to collide with one another; as a result, electrons are knocked off, and part of the cloud gradually accumulates a negative charge, and another part a positive charge. At some point, the excess electrons will “jump the gap” and discharge as lightning, which often remains completely within the cloud.
Similarly, in a volcanic eruption cloud, there are small particles of volcanic material colliding with one another at high speeds, and these collisions can result in separation of charges in the volcanic cloud that result in lightning.
Lightning is common at some volcanoes (Chaitin, Chile) but extremely rare in Hawaiʻi. For one week in July 2008, following unusually dry conditions, the ocean entry plume at Kalapana was particularly vigorous, and lightning was seen at night.
Is that a tornado in the background, or a waterspout?
Tornadoes form over dry land, so that's not a true tornado, but their formation is similar. Basically, the air in the plume is very hot and buoyant. As it rises, it draws more air in from underneath, but because the wind is blowing the plume sideways, the air from below gets pulled in sideways too, forming a vortex. When an eruption plume is over the land, it draws in cooler air from below and creates vortices too, but these are invisible. The ones over the ocean are visible because moisture from the ocean gets caught up in the vortex. Dust-devils are only apparent when dust is present; swirling leaves in a parking lot indicate local winds; water from the ocean exposes the presence of these eruption plume vortices. This is not a true waterspout, either: waterspouts connect to cumuliform clouds.