The Sunda Arc is a volcanic arc that produced the volcanoes that form the topographic spine of the islands of Sumatra, Nusa Tenggara, and Java, the Sunda Strait and the Lesser Sunda Islands. The Sunda Arc begins at Sumatra and ends at Flores, and is adjacent to the Banda Arc. The Sunda Arc is formed via the subduction of the Indo-Australian Plate beneath the Sunda and Burma plates at a velocity of 63–70 mm/year.
Formation and geologic setting
Mid-oceanic ridge basalts (MORB) form most of the oceanic basin south of Sunda, according to geodynamic studies. These plates began to converge in the Early Miocene. The Indo-Australian Plate is subducting beneath the Eurasian Plate with the dip angle of 49-56 degrees. The slab subducting under Java is continuous down to the lower mantle. However, the slab appears to beak apart under Sumatra Island. Earthquake depth records indicate that there is no deep seismic activity in Sumatra, likely due to the age of the subducting complex.. Two types of subductions have been identified along the Sunda Arc: 1) orthogonal subduction along Java and 2) oblique subduction on the Sumatra side. These subductions are separated by the Sunda Strait.
Notable seismic events
With the ongoing magmatic activities and the nature of the subduction zone, Sunda Arc experiences major seismic events throughout history. These events cost the loss of lives and vast destruction along the coast. These are some major seismic events that have been recorded.
Tsunami on December 2004, Indian Ocean
In 2004, the tsunami in Indian Ocean was triggered by an earthquake of 9.15 magnitude near Sumatra Island. In Banda Aceh area, the tsunami height reached up to 35 meters, which surpassed value recorded prior to this event.
Tsunami on July 2006, West Java and Central Java, Indonesia
A devastating event occurred on July 17, 2006, with major destruction along West Java and Central Java. The Mw-7.7 earthquake-induced tsunami struck over 250 km of the coastline and cost more than 600 deaths. The approximate run-up height was about 4–6 meters.
Historic eruptions and arc volcanism
The Sunda Arc is home to some of the world's most dangerous and explosive volcanoes. The 1815 eruption of Mount Tambora on Sumbawa and the 1257 eruption of Mount Samalas on Lombok were among the largest in the last two millennia, ranking 7 on the VEI scale. 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. 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.