The Sunda Trench

The Sunda Trench, earlier known as, and sometimes still indicated as the Java Trench, located in the northeastern Indian Ocean, with a length of 2,600 kilometres (8,500,000 ft) and a maximum depth of 7,725 metres (25,344 ft)[citation needed] (at 10°19'S, 109°58'E, about 320 km south of Yogyakarta), is the second-deepest point in the Indian Ocean after Diamantina Trench, which is 8,047 metres deep. It stretches from the Lesser Sunda Islands past Java, around the southern coast of Sumatra on to the Andaman islands, about 300 km off the coasts of Java and Sumatra, and forms the boundary between Indo-Australian Plate and Eurasian plate (more specific, Sunda Plate), is part of the Pacific Ring of Fire and a ring of oceanic trenches around the northern edges of the Australian Plate.

There is scientific evidence that the recent earthquake activity in the area of the Java Trench could lead to further catastrophic shifting within a relatively short period of time, perhaps less than a decade. This threat has resulted in international agreements to establish a tsunami warning system in place along the Indian Ocean coast
For about half its length, off of Sumatra, it is divided into two parallel troughs by an underwater ridge, and much of the trench is at least partially filled with sediments. Mappings after the 2004 Indian Ocean earthquake of the plate boundary showed resemblance to suspension bridge cables, with peaks and sags, indicative of asperity and locked faults, instead of the traditional wedge shape expected.

Some of the earliest exploration of the Trench occurred in the late 1950s when Robert Fisher, Research Geologist at the Scripps Institution of Oceanography, investigated the trench as part of a world wide scientific field exploration of the world's ocean floor and sub-oceanic crustal-structure. Bomb-sounding, echo-train analysis and manometer were some of the techniques used to determine the depth of the trench. The research contributed to an understanding of the subduction characteristic of the Pacific margins. Various agencies have explored the trench in the aftermath of the 2004 earthquake, and these explorations have revealed extensive changes in the ocean floor.

Sunda Arc

The Sunda Arc is a volcanic arc that has produced the islands of Sumatra and Java, the Sunda Strait and the Lesser Sunda Islands. A chain of volcanoes forms the topographic spine of these islands. The arc marks an active convergent boundary between the East Eurasian plates that underlie Indonesia, especially the Sunda Plate and the Burma Plate, with the India and Australian Plates that form the seabed of the Indian Ocean and the Bay of Bengal. The Sunda Arc is a classic example of a volcanic island arc, in which all the elements of such geodynamic features can be identified.

Western Sunda Arc and Trench showing tectonic and seismic activity
The India and Australian Plates are subducting beneath the Sunda and Burma plates along the Sunda Arc. The tectonic deformation along this subduction zone in the Java Trench (also known as the Sunda Trench) caused the 2004 Indian Ocean earthquake of December 26, 2004. The Sunda Arc is home to some of the world's most dangerous and explosive volcanoes. The eruption of Mount Tambora on Sumbawa Island, in 1815, is thought to be the most massive in recorded history. Also this subduction zone has created arguably the world's largest active volcano Lake Toba which produced the largest volcanic eruption in human history erupting just over 2,800 km³ of magma, a VEI of 8. The loudest noise in recorded history occurred during the 1883 eruption of Krakatoa and was heard 5,000 km (3,100 mi) away. Hundreds of thousands of people have been killed by these eruptions and by episodes of activity at other volcanoes, including Papandayan, Galunggung, and Kelut.

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