Located in East Java, Gunung Semeru is the highest mountain on the Indonesian island and one of the world's most active volcanoes. Also known as Mahameru (Great Mountain), it rises steeply 12,060 feet above the southern end of the Tengger Caldera and has formed tuff cones containing crater lakes along a line through its peak.
Since 1967, Mt Semeru has been in an almost constant state of eruptions that commonly occur every 20 to 30 minutes, the ash columns reaching heights of 1,000 to 1,600 feet above the crater. Usually, the eruption clouds are blown away by the wind, while pyroclastic flows often follow the larger eruptions. At least 55 outbreaks consisting of lava flows have been recorded since 1818, 10 of which resulted in deaths.
Gunung Semeru is frequently climbed by tourists, and the landscape on the way is somewhat unearthly as you hike through the huge Sand Sea caldera that comprises other volcanoes such as Mt Bromo and Mt Batok. The Semeru volcano is a must for every mountaineer who travels around Indonesia.
Although not too technical, the hike can be dangerous due to poisonous sulfuric fumes and the possibility of an eruption. The tour usually starts from the small village of Ranu Pane in the north, from where you reach the summit of Mt Semeru within two days. On the first day, you get to Camp Arcopodo, around 9,500 feet above sea level, and the next day to the peak and back. It is also possible to hike to the lower Camp Kalimati (8,500 feet) on the first day; however, the ascent on the steep cinder cone the next morning is more arduous.
The nearest domestic air facility is in Surabaya, from where it is a 3 to 4-hour drive via Pasuruan/Probolinggo, Sukapura, Ngadisari and the village of Cemoro Lawang. Alternatively, you can take a direct flight from Jakarta to Malang (2 hours) and access Ranu Pane by minibus via Tumpang and Gubug Klahkah.