The Java Trench is a continuation of the Sunda Trench, where the oceanic part of the Australian Plate is being subducted beneath the continental Eurasian Plate. A string of volcanoes has resulted behind the trench, strung out across Sumatra, Java, and the Lesser Sunda Islands. The Australian Plate is moving north at a rate of 2.5 in (6 cm) per year. The Indian Ocean floor south and west of the Java Trench shows tectonic features aligned in this northerly direction. Between Investigator Ridge and Ninetyeast Ridge lie a series of north–south fractures formed to accommodate different rates of motion in the Australian and Indian plates. The Ninetyeast Ridge itself is the longest underwater mountain chain, at 3,100 miles (5,000 km) in length. It followed in the wake of India’s rapid motion north as the Indian Ocean opened up. The ridge represents piles of extruded volcanic material formed above the Kerguelen Hotspot, and were carried north as the sea floor spread between India and Antarctica.