Ultra-high-speed footage of three lightning strikes, triggered by an initial cloud-to-ground event (left). The first strike is a positive cloud-to-ground lightning strike (with continuing current), which triggers upward discharges from three 200-metre-tall TV towers. Also visible are the extremely fast recoil leaders which retrace the leader channels. Filmed at 9000 frames per second, in Rapid City, South Dakota, USA, in summer.