Merapi is one of the most active volcanoes in Indonesia (2,948 m summit elevation). Eruptions during the twentieth and twenty-first centuries resulted in: 1,369 casualties (1930-1931), 66 casualties (1994) (Thouret et al., 2000), and 386 casualties (2010). The 2010 eruption had impacts that were similar to the unusually large 1872 eruption, which had widespread impacts and resulted in approximately 200 casualties (Hartmann, 1934). These casualties are considered to be a large number given the relatively sparse population in the late nineteenth century by comparison with the population density today.

The 5 November 2010 Merapi eruption affected two provinces and four regencies, including Magelang (west-southwest flank), Sleman (south flank), Klaten (southeast-east flank, and Boyolali (northern flank). The eruption led to the evacuation of 399,000 people and resulted in a total loss of US$ 3.12 billion (National Planning Agency: National Disaster Management Agency, 2011-2013).

The large number of evacuees of Merapi in 2010 was due to warnings of an unusually large eruption – a warning that was based on precursors during the months to days preceding the eruption. These precursors included large increases in seismicity and deformation of the volcano's summit, high rates of dome extrusion, increased temperature of crater fumaroles (reaching 460ºC by 20 October), and an abrupt increase in CO2 at a summit fumaroles. During the time of crisis, there was rapid escalation in rates of seismicity, deformation and rates of initial lava extrusion. All the monitoring parameters exceeded levels and rates of change observed during previous eruptions of the late twentieth century. Consequently, a Level IV warning was issued and evacuations were carried out and then extended progressively to greater distances as the activity escalated. The exclusion zone was extended from 10 to 15 and then to 20 km from Merapi's summit.