Large volcanic lightning can form in the eruption plume and are often a great spectacle. Lightning is formed due to differently charged particles within the plume. The charge can be created by several different processes and settings for the plume, such as from ice particles in the plume, friction created by colliding tephra fragments (and ice if present), break up of tephra particles, radioactive charging, and the height of the plume plays a part as well. Lightning is one of the more dangerous hazards connected to eruptions and can pose a threat tens of kilometers away from the eruption. This is especially true for eruptions in Katla volcano, with two fatalities about 30 km distance from the volcano during the 1755 eruption and often a loss of livestock during eruptions. 

In the Eyjafjallajökull eruption, the abundance of water, ice and tephra in the plume, especially during phase I and III, created good conditions for lightning in the eruption plume. It seems though that the height of the plume itself and the -20°C isothermal line played a major role in lightning generation, as the upper part of the plume got colder, lightning became more frequent. During the eruption, 790 lightning was detected, most of them during phase I and III of the eruption with peak activity on the 17th of April and 16th of May. Most of the lightning occurred close to the crater, less than 3 km distance from it, but luckily no damage was recorded due to lightning during the eruption.