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. The resulting caldera has become Lake Toba. The loudest noise in recorded history occurred during the 1883 eruption of Krakatoa and was heard away. 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. Main-arc volcanism The main-arc volcanism along Sunda is mainly derived from the interaction between the Indo-Australian Plate and the Eurasia Plate. Magma originates from partial melting of the mantle wedge driven by the fluids from subducting slab. In addition, volcanic rocks from Quaternary generally show more enrichment in alkaline contents than those from Tertiary age. The majority of basalts of the arc have calc-alkaline contents, except for some potassic lava production in East Java. Back-arc volcanism The magmatic activities along the back-arc may or may not relate to the main-arc materials. Magma and lava appear to have originated from molten materials at a deeper part of the mantle as supported by a higher K2O/Na2O ratio in comparison to other part of Sunda Arc. Most salient volcanoes in back-arc region are Lasem, Muria, and Bawean in which their volcanic rocks show complex patterns in terms of chemical signature. Major islands Java Java Island is located on the east side of Sunda Arc, residing between Sumatra and Bali. Its oceanic crust's thickness is approximately 20-25 kilometers. With the geological activities and the tectonic nature of Sunda Arc, megathrust earthquakes and volcanic activities are ubiquitous at Java island. Modern volcanoes at Java are formed during Tertiary with typical products of andesitic composition and progressively get more alkali content during Quaternary. Along the Java island, there are approximately 62 geothermal fields which can be utilized for further usages including producing electricity. Java is also a germinal center for supplying gold and cooper in which the occurrences of these low-sulfidication (LS) epithermal deposits may associate with magmatic arc activities with the spatial relationship between the akaditic magma and porphyry Cu-Au deposits. East Java Most volcanic activity in East Java is Plinian-type, which is very explosive and emits columns of hot volcanic debris. The adiakitic magma, which deviates from usual island-arc magma, is associated with porphyry deposits. There is evidence that the Ringgit-Beser volcanic complex also produces potassic and magnesian