Residents wearing surgical masks to protect themselves against ash from Calbuco volcano, walk by the Patagonian Argentine area of San Martin de Los Andes

Residents wearing surgical masks to protect themselves against ash from Calbuco volcano, walk by the Patagonian Argentine area of San Martin de Los Andes

Residents wearing surgical masks to protect themselves against ash from Calbuco volcano, walk by the Patagonian Argentine area of San Martin de Los Andes April 23, 2015. Volcano Calbuco in southern Chile that erupted unexpectedly on Wednesday was still pouring ash into the sky on Thursday, forcing the cancellation of flights from nearby towns in both Chile and neighboring Argentina.The volcano, which last had a major eruption in 1961, has blown a spectacular plume of ash and smoke nearly 20 kilometers into the sky near Puerto Varas, some 1,000 kilometers (625 miles) south of Santiago. REUTERS/Patricio Rodriguez