[2] Mid-oceanic ridge basalts (MORB) form most of the oceanic basin south of Sunda, according to geodynamic studies.

[5][6] Earthquake depth records indicate that there is no deep seismic activity in Sumatra, likely due to the age of the subducting complex.

[9] With the ongoing magmatic activities and the nature of the subduction zone, Sunda Arc has experienced major seismic events throughout history.

[14] The Sunda Arc subduction zone was also the site of one of the largest known eruptions of the Cenozoic, the VEI 8 Toba supereruption on Sumatra, which expelled 2,800 km3 of magma c. 74,000 BP.

[16] Hundreds of thousands of people have been killed by these eruptions and by episodes of activity at other volcanoes, including Papandayan, Galunggung, Merapi, Kelud, Sinabung, and Agung.

[17] In addition, volcanic rocks from the Quaternary generally show more enrichment in alkaline contents than those from the Tertiary age.

[3][17] The most salient volcanoes in the back-arc region are Lasem, Muria, and Bawean in which their volcanic rocks show complex patterns in terms of chemical signature.

[20] Modern volcanoes at Java are formed during the Tertiary with typical products of andesitic composition and progressively get more alkali content during the Quaternary.

[23] There is evidence that the Ringgit-Beser volcanic complex also produces potassic and magnesian lava, which could be a result of the decreasing influence of subduction-related material.

Mount Merapi is a steep stratovolcano situated on Central Java Island with seismic and volcanic activities that could pose major threats to countless lives and infrastructures in its vicinity.

[32] Most recent volcanic activities are induced by the collapse of the lava dome, contributing to the highly explosive eruption of andesitic materials.

[37] The geochemical study of major and trace elements and isotopic signatures of lava have confirmed the steady-state subduction and ongoing replenishment of magma for about 10 Ma.

[36] The basement of West Java is a continental lithosphere which can be inferred from crustal assimilation and contamination in volcanic rocks.

[6] A K/Ar study reveals that subducted-related magmatism in Sumatra started roughly in the early Mesozoic according to the evidence derived from the plutonic body on Barisan Mountain.

[46] Mount Sinabung is a stratovolcano of andesite and dacite in the Karo plateau of North Sumatra, 40 kilometres (25 mi) from the Lake Toba supervolcano.