Typology of Indonesian Stratovolcanoes: Insights from Geomorphological and Geological Aspects

Abstract

Stratovolcano is the most dominant volcano type in Indonesia; however, our understanding of the correlation between geomorphological and geological aspects on stratovolcano is still lacking. To reduce such a gap, we provide the first general typology of Indonesian stratovolcano (number of analyses=154). Several parameters were evaluated, including average radius (r), average slope (S), surface roughness (RMS), bulkrock compositions, mineralogy, and deposit characteristics. Four types were identified: (1) small-least dissected cones, (2) broad-dissected cones, (3) extremely broad-dissected cones with caldera, and (4) residual-highly dissected cones. Type I is typically small (r=2.1 km), steep (S=19.80°), rough (RMS=88.8), dominated by basic to intermediate rocks, having abundant mafic minerals with minor hydrous minerals, and primarily consisting of lava flows and scoria. Type II has moderate values of r, S, and RMS(8.8 km, 15.2°, and 47.7, respectively), predominantly intermediate in composition, poor in mafic minerals and rich in hydrous minerals, and having abundant pumice and lava domes. Type III is typically large (r=18.1 km), gently-sloped (S=9.2°), smooth (RMS=40.1), rich in felsic rocks and felsic minerals, and includes thick ignimbrite deposits. Type IV has moderate size (r=8.2 km), is gently-sloped (S=10.7°), rough (RMS=56.8), and rich in ultrabasic rocks and mafic minerals with common exposure of intrusions. We conclude that the evolution from type I to III corresponds to the maturation stage, whereas the formation of type IV represents the erosional stage. Moreover, rainfall precipitation degree (Pr) also controls stratovolcano morphology, where higher Pr decreases S and RMS values, and increase r value.