Indonesia covers 30° along equator from east to west, and the end points happen to be the locations of main convection rolls division lines. Tracing the western division line further south, it leads to the most active volcano of Indonesia, Mount Merapi.
This indicates an interplay between the subduction of crust material and the mantle convection activity. The few facts shown on the map, a span of 30° along equator and the location of Merapi, already give us some insight into the geology of Indonesia. By further analyzing the effect of upper convection rolls (with 1.5° interval) much more will be revealed about the real nature of volcanism, geothermal activity and the tectonic framework in general.