An extensive smoke and ash plume, originating from various wildfires in the Riau province on Sumatra island, Indonesia, is visible on this 300 m image of 20 June 2013. At the day of observation, the fires (reported to be hundreds of separate fires) already lasted for five days. A warning was raised by the Indonesian National Board for Disaster Management (BNPB) to neighbouring countries Malaysia and Singapore for the approach of chocking smog. June is the start of the yearly forest fire season, when slash-and-burn techniques are used to clear land quickly and cheaply, often for palm oil plantations.