The Andaman Trench

One undersea trench explains two very different things: India’s only active volcano, and its worst natural disaster in living memory.

mcqquestion.com

Indian Geography · IndGeo0066

The Andaman Trench

One subduction zone, six landforms, west to east

1 · Foredeep

Andaman Trench

Max. depth ~4,198 m

→

2

Accretionary Prism

Scraped sediment piles up

→

3 · Island Arc

Andaman & Nicobar Is.

Exposed above sea level

→

4

Fore-arc Basin

→

5 · Volcanic Arc

Barren Island

India’s only active volcano

→

6 · Back-arc

Andaman Sea

Seafloor spreading apart

Indian Plate subducts beneath the Burma microplate — west (left) to east (right)

One fault, one disaster

On 26 December 2004, this subduction zone ruptured for about 1,200 km, pushing the seafloor up by up to 10 metres. The resulting tsunami struck the Andaman and Nicobar Islands, and made Indira Point, India’s southernmost point, subside by about 4.25 metres.

mcqquestion.com · Indian Geography ⬇ Download as image

Must Know

• The Andaman Trench lies in the northeastern Indian Ocean, just west of the Andaman and Nicobar Islands.
• It is the northern segment of the much larger Sunda Trench system.
• It forms where the Indian Plate subducts, or slides beneath, the Burma microplate.
• Its maximum depth is about 4,198 metres.

Good to Know

• The trench is just one part of a full subduction zone system, laid out west to east.
• First comes the trench itself, called the foredeep, where the two plates actually meet.
• Next comes an accretionary prism, where scraped-off sediment piles up.
• Then comes the island arc, the visible ridge above sea level. The Andaman and Nicobar Islands are this island arc’s exposed peaks.
• Further east lie a fore-arc basin, then the volcanic arc, home to Barren Island, India’s only active volcano.
• Finally comes the back-arc basin, where the Andaman Sea itself is slowly spreading apart.

Test Yourself

Please wait…

1. The Andaman Trench forms where the Indian Plate subducts beneath which other plate?

The Burma microplate

The Australian Plate

The Eurasian Plate

The Arabian Plate

 Loading…

 

Great to Know

• On 26 December 2004, a massive magnitude 9.1 earthquake ruptured along this subduction zone.
• The rupture ran for about 1,200 km, from off the coast of Sumatra up into the Andaman segment.
• It pushed the seafloor up by as much as 10 metres in places, displacing huge volumes of water.
• That displacement triggered the devastating 2004 Indian Ocean tsunami.
• The tsunami struck the Andaman and Nicobar Islands directly, since they sit right above this same fault system.
• It also caused the land around Indira Point, India’s southernmost point, to subside by about 4.25 metres.