See this spectacular video of lightning strikes near the eruption of a volcano on Mount Kirishima, which was shot by a nearby bystander. Be sure to go to full screen mode.
The Shinmoedake volcano on Mt. Kirishima, located on the Kyushu main island of southern Japan has erupted for three straight days, sending potentially hazardous ash and smoke into the air of towns nearby. News reports say this is its biggest eruption in 50 years.
For an explanation of how volcanoes cause lightning, Jearl Walker in his book The Flying Circus of Physics writes about a similar case of brilliant flashes of lightning dancing around the Icelandic volcano Surtsey in 1963.
“The hot lava hitting the seawater sends positively charged steam upward. After sufficient charge separation has occurred, the clouds of steam discharge back to the ocean, allowing electrons to flow upward through the ionization column. The upward flow of electrons is opposite the situation with normal lightning.”
In the case of Mt. Kirishima, fog and moist air from the nearby sea might be generating enough steam to create the flashes of lightning seen in the video. As National Geographic points out, scientists still aren’t sure what exactly causes the spectacular strikes of lightning near volcanos.