Shatsky Rise

The Shatsky Rise is Earth's third largest oceanic plateau, (after Ontong Java and Kerguelen) located in the north-west Pacific Ocean 1,500 km (930 mi) east of Japan. It is one of a series of Pacific Cretaceous large igneous provinces (LIPs) together with Hess Rise, Magellan Rise, and Ontong Java-Manihiki-Hikurangi. It was named for Nikolay Shatsky (1895-1960), a Soviet geologist, expert in tectonics of ancient platforms.

The rise consists of three large volcanic massifs, Tamu, Ori, and Shirshov, but, in contrast, there are few traces of magmatism on the surrounding ocean floor. The Tamu Massif may be the largest volcano yet discovered on Earth.

It covers an area that has been estimated to c. 480,000 km² (190,000 sq mi) (roughly the size of California) and a volume of c. 4,300,000 km³ (1,000,000 cu mi). Beneath Shatsky rise, however, the Mohorovičić discontinuity (Moho, the mantle-crust boundary) disappears at a depth of 20 km (12 mi) whereas it is normally observed at a depth of 17 km (11 mi). Furthermore, the crustal thickness between the massifs of the Shatsky Rise is almost twice that of normal crust thickness. This considered, the area covered by the rise, assuming the crust was also formed by the Shatsky Rise volcanism, has been estimated to 533,000 km² (206,000 sq mi) and the volume to 6,900,000 km³ (1,700,000 cu mi).

After its formation Shatsky Rise was uplifted 2,500–3,500 m (8,200–11,500 ft) and it then subsided 2,600–3,400 m (8,500–11,200 ft), which, in both cases, is considerably more than in the case the Ontong-Java Plateau. There was least subsidence at the centre of the Tamu Massif (c. 2,600 m (8,500 ft)), subsidence increased at the northern flank of the Tamu Massif and at the Ori Massif (c. 3,300 m (10,800 ft)), and it becomes greatest at the flank of Ori Massif. The cause of this gradual increase in subsidence can be underplating beneath Tamu Massif. There was much less subsidence at Shirshov Massif farther north (c. 2,900 m (9,500 ft)) which probably represents a later, different phase of volcanism.

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