Moi, Paul Derand

Merapi is a sub-plinian volcano in central Java, in Indonesia.

It is one of the most dangerous of the world (it has a dangerosity of 6,2 as it has frequent strong eruption (it has a VAI of 2,06, which is a lot) and an important population on its lower flanks. It can threaten about one million people with moderate ashfall and 100K people with heavy ashfall. Merapi produces more pyroclastic flows than any other volcano in the world  The problem is that most pyroclastic flows and lahars tend to flows on the SW flanks, the most populated one, so that high lahars can affect half a million, moderate ones can affect a million, pyroclastic flows can affect half a million people on the SW side and 100K people on the north and east.

Moreover, the volcano is steep-sided and a sector collapse, with debris avalanche occurs statistically every 2000 to 7000 years.

Here is a detailed website I found. The summary of the estimated population exposed to Merapi hazards I gave you above came from here. The website describes Merapi's volcanic hazards, with a risk map, the frequency of different volcanic hazards.... Moreover, it gives some solutions on how to make those hazards less dangerous: sabo dams against lahars, better roof structures to prevent roof collapse from heavy and moderate ashfall...