Shatsky Rise facts for kids
The Shatsky Rise is a massive, flat-topped underwater mountain range, also known as an oceanic plateau. It's the third largest of its kind on Earth, found deep in the northwest Pacific Ocean, about 1,500 km (930 mi) (930 miles) east of Japan. Imagine a huge, flat table sitting on the ocean floor!
This incredible underwater feature is one of several "large igneous provinces" (LIPs) in the Pacific. This means it was formed by enormous eruptions of molten rock (lava) from deep inside the Earth, creating vast areas of volcanic rock. The Shatsky Rise was named after Nikolay Shatsky, a Soviet geologist who studied ancient Earth structures.
The Shatsky Rise is made up of three giant underwater volcanoes: Tamu, Ori, and Shirshov. What's amazing is that Tamu Massif is thought to be the single largest volcano ever discovered on Earth! In 2016, scientists found that Tamu Massif alone covers an area of about 533,000 square kilometres (206,000 sq mi). That's bigger than the famous Olympus Mons volcano on Mars!
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Exploring the Shatsky Rise: An Underwater Giant
The main part of the Shatsky Rise is a diagonal plateau. It stretches across a huge area of the Pacific Ocean. Including its edges and the Papanin Ridge, it covers a vast region.
How Big is This Ocean Plateau?
Scientists estimate the central area of the Shatsky Rise covers about c. 480,000 km2 (190,000 sq mi). To give you an idea, that's roughly the size of California or Sumatra! The total volume of rock in this plateau is around c. 4,300,000 km3 (1,000,000 cu mi).
Deep beneath the Shatsky Rise, the boundary between Earth's crust and mantle, called the Mohorovičić discontinuity (or Moho), is found at a depth of about 20 km (12 mi). This is deeper than the usual 17 km (11 mi) for normal ocean crust. Also, the crust between the giant volcanoes of the Shatsky Rise is almost twice as thick as typical ocean crust. If we consider all the crust formed by the Shatsky Rise's volcanic activity, its total area could be 533,000 km2 (206,000 sq mi), with a volume of 6,900,000 km3 (1,700,000 cu mi).
Why Did Parts of It Rise and Sink?
After it first formed, the Shatsky Rise was pushed upwards by 2,500–3,500 m (8,200–11,500 ft). Then, it slowly sank downwards by 2,600–3,400 m (8,500–11,200 ft). These changes were much larger than those seen in other ocean plateaus like the Ontong-Java Plateau.
The least amount of sinking happened at the center of the Tamu Massif, about c. 2,600 m (8,500 ft). The sinking increased towards the northern side of Tamu Massif and at the Ori Massif, reaching about c. 3,300 m (10,800 ft). This gradual increase in sinking might be due to magma (molten rock) collecting and hardening beneath the Tamu Massif. The Shirshov Massif, further north, sank less, about c. 2,900 m (9,500 ft). This suggests it might have formed during a different, later period of volcanic activity.
The Ancient Story of Its Formation
The Shatsky Rise formed a very long time ago, during the Late Jurassic and Early Cretaceous periods. It grew at a special place where three of Earth's giant tectonic plates met: the Pacific Plate, the Farallon Plate, and the Izanagi Plate. This meeting point is called a "triple junction." Scientists believe it might be the oldest ocean plateau that hasn't changed much since it formed.
Because it formed before a long period without magnetic reversals (when Earth's magnetic field flips), scientists can figure out its age very precisely. Magnetic patterns in the rocks around Shatsky Rise show its age ranges from about 147 million years ago (Ma) at its southwest edge to 124 Ma at its northern tip.
How Earth's Plates Shaped the Rise
The massive eruptions that created the Shatsky Rise happened at the Pacific–Farallon–Izanagi triple junction between about 147 and 143 Ma. This could have happened because a super-hot column of rock, called a mantle plume, rose from deep inside Earth. Or, it might have been due to molten rock forming at a mid-ocean ridge (an underwater mountain range where new ocean floor is created).
This huge eruption happened at the same time as a big shift in the triple junction's location. It jumped about 800 km (500 mi) (500 miles) in nine stages! This also changed how the plates were interacting at that spot.
Magnetic patterns, known as the Hawaiian lineations, formed between Shatsky Rise, Hess Rise, and the Mid-Pacific Mountains. These patterns show how the Pacific and Farallon plates spread apart between 156 and 120 Ma. North of Shatsky Rise, other magnetic patterns, called the Japanese lineations, point in a different direction. The differences in these patterns help scientists trace the path of the Pacific–Farallon–Izanagi triple junction over time.
The triple junction moved northwest before 150 Ma. Then, it reorganized, a small piece of crust (a microplate) formed, and the triple junction made a big 800 km (500 mi) (500-mile) jump eastward. This jump led to the formation of the oldest part of the rise, the TAMU Massif. The rest of the Shatsky Rise formed later, following the path of the triple junction. The volcanic activity that built Shatsky Rise happened in bursts, linked to at least nine of these ridge jumps.
The Giant Volcanoes of Shatsky Rise
The amount of rock in the Shatsky Rise decreases as you move along the path of the triple junction. The TAMU Massif, at the southern end, is the largest, with an estimated volume of 2,500,000 km3 (600,000 cu mi). The Ori and Shirshov massifs, which formed around 136 Ma, each have a volume of about 700,000 km3 (170,000 cu mi). The Papanin Ridge, at the northern end of the rise, has a volume of 400,000 km3 (96,000 cu mi). It likely formed over a longer period, between 131 and 124 Ma.
The parts of the Shatsky and Hess rises that were on the Farallon Plate are thought to have been involved in a period of mountain building called the Laramide orogeny. These parts likely slid beneath (or "subducted") North America and northern Mexico.
