Mountains are formed as a result of rising of low density rock layers which formed in the high density molten rock.
When the molten rock material under the earth surface cools down and hardens to form rocks, hot gases and water are released from it. This produces rocks of lesser density from high density molten rock.
A thing of lesser density will float in a liquid of higher density.
Hence, when the newly formed rocks of lesser density in the high density molten rock below the Indonesian islands rise upwards to form the mountains.
for example cyprus is an island in the mediteranean sea.
at the center of the island a huge mountain range calles as troodos mountains are formed.
in the same manner all the mountains were formed.
it is not correct ot say that mountains are formed as aresult of collision of land surface.
Cyprus is the Mediterranean's third largest island and situated in the eastern par of the Mediterranean sea,south of Turkey and west of Syris and Lebanon.
it should be noted that a magnitude of 4.4 earthquake struck the island on Wed Sep 16, 2009 ,near the south coast.
this proved that the rising of island resulted in earthquakes.