Indonesia is situated in the “Pacific Ring of Fire”, which is surrounded by volcanoes and vulnerable from volcanic eruptions. Since the population development, the volcanic environment then occupied by settlements or agricultural fields.
It is important to provide the peoples and decision makers the hazardous map or rapid assessment map for new safety zone.
With the availability of free open source software GRASS and free download-able DEM (e.g. ASTER GDEM), it is possible to generate new base-line of hazardous map.
In this map, we assume that the main river will provides the new base-line for new safety zone of volcanic eruptions. Study site Mount Sinabung, Karo Regency, North Sumatera Indonesia.
Originated from Pleistocene-to-Holocene geological ages, this stratovolcano located 40 km from Lake Toba, which was “born” from Toba Supervolcano. Recently, Mount Sinabung was erupted in January and February 2014. The other eruptions were September and November 2013, 29 August 2010, the year 1912, and the year 1600.
The main rivers was generated using Horton Stream Order. Further analysis of new safety zone should begin from this base-line. Our assumption is when the debris flow from the summit, it will flow through the streams and follow the topographic condition.
The main streams is indicated with the highest number (No. 4), while the other streams are No. 1, 2, and 3. The main streams is situated surrounding the Mount Sinabung with radius around 3 km from the summit in the north side, to about 5 km from the summit in the southern part. Combination of radial and annular pattern of streams were identified in the Mount Sinabung environment.
This method can provide zonation with minimum data requirements. However, further analysis should be conducted to provide the peoples with the integrated zonation of hazardous map such as susceptibility mapping of debris flows and other gravitational hazards (e.g. Landslide)