地球上存在大型单体火山

A University of Houston (UH) professor led a team of scientists to uncover the largest single volcano yet documented on Earth. Covering an area roughly equivalent to the British Isles¹ or the state of New Mexico, this volcano, dubbed² the Tamu Massif, is nearly as big as the giant volcanoes of Mars, placing it among the largest in the Solar System. William Sager³, a professor in the Department of Earth and Atmospheric⁴ Sciences at UH, first began studying the volcano about 20 years ago at Texas A&M's College of Geosciences. Sager and his team's findings appear in the Sept. 8 issue of Nature Geoscience, the monthly multi-disciplinary journal reflecting disciplines within the geosciences.

 

Located about 1,000 miles east of Japan, Tamu Massif is the largest feature of Shatsky Rise, an underwater mountain range formed 130 to 145 million years ago by the eruption⁵ of several underwater volcanoes. Until now, it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points. By integrating several sources of evidence, including core samples and data collected on board the JOIDES Resolution research ship, the authors have confirmed that the mass of basalt（玄武岩） that constitutes Tamu Massif did indeed erupt from a single source near the center.

 

"Tamu Massif is the biggest single shield volcano ever discovered on Earth," Sager said. "There may be larger volcanoes, because there are bigger igneous⁶ features out there such as the Ontong Java Plateau, but we don't know if these features are one volcano or complexes of volcanoes."

 

Tamu Massif stands out among underwater volcanoes not just for its size, but also its shape. It is low and broad, meaning that the erupted lava⁷ flows must have traveled long distances compared to most other volcanoes on Earth. The seafloor is dotted with thousands of underwater volcanoes, or seamounts（海底山）, most of which are small and steep compared to the low, broad expanse of Tamu Massif.

 

"It's not high, but very wide, so the flank slopes are very gradual," Sager said. "In fact, if you were standing⁸ on its flank, you would have trouble telling which way is downhill. We know that it is a single immense volcano constructed from massive lava flows that emanated⁹ from the center of the volcano to form a broad, shield-like shape. Before now, we didn't know this because oceanic plateaus are huge features hidden beneath the sea. They have found a good place to hide."

 

Tamu Massif covers an area of about 120,000 square miles. By comparison, Hawaii's Mauna Loa -- the largest active volcano on Earth -- is approximately 2,000 square miles, or roughly 2 percent the size of Tamu Massif. To find a worthy¹⁰ comparison, one must look skyward to the planet Mars, home to Olympus Mons. That giant volcano, which is visible on a clear night with a good backyard telescope, is only about 25 percent larger by volume than Tamu Massif.

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