mount sinabung, north sumatra, indonesia

acidic activity amazing andesite around berastagi climbing crater crystalline deleng discolouration dolok eruption gases geothermal goals gunung high hiker hiking hot indonesia indonesian karo lake mount mountain nature north outdors plateau pleistoceneholocene regency seepage sibayak sinaboen sinaboeng sinabuna sinabung springs steam stratovolcano sulfur sulfurous sumatra travel traveler vents volcano