Advertisement The sky above an erupting volcano in Indonesia has turned a stunning electric purple during a lightning storm. Spectacular images captured the spectacle as Mount Sinabung in Karo, North Sumatra, continued to spew a column of ash and smoke up to 16,400ft (5km) into the sky as lightning bolts crackled above. Sinabung leapt back into life last week, with 13 separate blasts on Tuesday alone, and it continued to shoot volcanic debris for several days afterwards. The purple skies - which can be caused by the scattering of white light due to moisture, haze and dust in the air - were captured by photographers on Friday using long exposures.