12December2017

Earth’s Largest Volcano Discovered

SUMMARY

  1. The entirety of Tamu Massif is bigger than the British Isles or New Mexico.
  2. Tamu is 400 miles wide but only about 2.5 miles tall. It erupted for a few million years during the early Cretaceous period, about 144 million years ago, and has been extinct since then, the researchers report.
  3. The world’s biggest volcano has been hidden because it sits on thin oceanic crust, which can’t support its weight. Its top is about 6,500 feet below the ocean surface.
Olympus Mons (pictured) is regarded as the largest volcano in the Solar System, but there is a new kid on the block. NASA

Olympus Mons (pictured) is regarded as the largest volcano in the Solar System, but there is a new kid on the block. NASA

Scientists say that they have discovered the single largest volcano in the world, a dead colossus deep beneath the Pacific waves.

A team writing in the journal Nature Geoscience says the 310,000 sq km (119,000 sq mi) Tamu Massif is comparable in size to Mars’ vast Olympus Mons volcano – the largest in the Solar System.

The Tamu massif is comparable in size to Olumpus Mons on Mars

The Tamu massif is comparable in size to Olumpus Mons on Mars

Called the Tamu Massif, the enormous mound dwarfs the previous record holder, Hawaii’s Mauna Loa, and is only 25 percent smaller than Olympus Mons on Mars, the biggest volcano in Earth’s solar system, said William Sager, lead study author and a geologist at the University of Houston.

“We think this is a class of volcano that hasn’t been recognized before,” Sager said. “The slopes are very shallow. If you were standing on this thing, you would have a difficult time telling which way was downhill.”

  • The structure topples the previous largest on Earth, Mauna Loa in Hawaii.
  • The massif lies some 2km below the sea.
  • It is located on an underwater plateau known as the Shatsky Rise, about 1,600km east of Japan.

It was formed about 145 million years ago when massive lava flows erupted from the centre of the volcano to form a broad, shield-like feature.

A volcanic giant at the bottom of the Pacific Ocean.:  Willam Sager/Nature Geoscience

A volcanic giant at the bottom of the Pacific Ocean.: Willam Sager/Nature Geoscience

The researchers doubted the submerged volcano’s peak ever rose above sea level during its lifetime and say it is unlikely to erupt again.

“The bottom line is that we think that Tamu Massif was built in a short (geologically speaking) time of one to several million years and it has been extinct since,” co-author William Sager, from the University of Houston, US, told the AFP news agency.

“One interesting angle is that there were lots of oceanic plateaus (that) erupted during the Cretaceous Period (145-65 million years ago) but we don’t see them since. Scientists would like to know why.”

Prof Sager began studying the structure two decades ago, but it had been unclear whether the massif was one single volcano or many – a kind that exists in dozens of locations around the planet.

While Olympus Mons on Mars has relatively shallow roots, the Tamu Massif extends some 30 km (18 miles) into the Earth’s crust.

And other volcanic behemoths could be lurking among the dozen or so large oceanic plateaux around the world, he thought.

“We don’t have the data to see inside them and know their structure, but it would not surprise me to find out that there are more like Tamu out there,” said Dr Sager.

“Indeed, the biggest oceanic plateau is Ontong Java plateau, near the equator in the Pacific, east of the Solomons Islands. It is much bigger than Tamu — it’s the size of France.”

The name Tamu comes from Texas A&M University, where Prof Sager previously taught before moving to the University of Houston.

Explaining ocean plateaus

Like other massive volcanoes, Tamu Massif seems to have a central cone that spewed lava down its broad, gentle slopes. The evidence comes from seismic surveys and lava samples painstakingly collected over several years of surveys by research ships. The seismic waves show lava flows dipping away from the summit of the volcano. There appears to be a series of calderas at the summit, similar in shape to the elongated and merged craters atop Mauna Loa, Sager said.

Until now, geologists thought Tamu Massif was simply part of an oceanic plateau called Shatsky Rise in the northwest Pacific Ocean. Oceanic plateaus are massive piles of lava whose origins are still a matter of active scientific debate. Some researchers think plumes of magma from deep in the mantle punch through the crust, flooding the surface with lava. Others suggest pre-existing weaknesses in the crust, such as tectonic-plate boundaries, provide passageways for magma from the mantle, the layer beneath the crust. Shatsky Rise formed atop a triple junction, where three plates pulled apart.

While Olympus Mons is much taller (>25km) than Tamu Massif (about 4km), its base is smaller. Massive lava flows would have rapidly flowed along shallow slopes to create Tamu Massif, which has a 650km-wide base, nearly as big as New Mexico in the US. Volcanoes created entirely due to such lava flow are called shield volcanoes because they resemble a warrior’s shield.

Tamu Massif, the inactive volcano, was previously thought to be a string of volcanoes rather than one enormous feature. It is part of an underwater mountain range called the Shatsky Rise, which covers an area as large as California state in the US. Found close to the east of the coast of Japan, Shatksy Rise formed some 145 million years ago as huge amounts of magma flowed onto the ocean floor at a point where three microplates of Earth’s crust meet.

Tamu Massif’s new status as a single volcano could help constrain models of how oceanic plateaus form, Sager said. “For anyone who wants to explain oceanic plateaus, we have new constraints,” he told LiveScience. “They have to be able to explain this volcano forming in one spot and deliver this kind of magma supply in a short time.”

Although rocks from Tamu Massif had previously been identified as volcanic crystallised lava, its size made geologists believe it was the result of many volcanic eruptions that may have occurred over a period of many millions of years. Now it seems that this may have been closer to a distinct but enormous flood of lava.

To verify that hypothesis Sager’s team collected new samples and data aboard an ocean-going science research vessel called Marcus G. Langseth. They drilled samples from the ocean floor, and poked Tamu Massif with seismic waves, measuring the response using seismometers. They were able determine whether the rocks may have come from different eruptions. From all the new data they acquired it seems that lava flow emerged from a single central magma vent.

Sager said other, bigger volcanoes could be awaiting discovery at other oceanic plateaus, such as Ontong Java Plateau, located north of the Solomon Islands in the southwest Pacific Ocean. “Structures that are under the ocean are really hard to study,” he said.

Floating volcano

Oceanic plateaus are the biggest piles of lava on Earth. The outpourings have been linked to mass extinctions and climate change. The volume of Tamu Massif alone is about 600,000 cubic miles. The entire volcano is bigger than the British Isles or New Mexico.

Despite Tamu’s huge size, the ship surveys showed little evidence the volcano’s top ever poked above the sea. The world’s biggest volcano has been hidden because it sits on thin oceanic crust (or lithosphere), which can’t support its weight. Its top is about 6,500 feet below the ocean surface today.

“In the case of Shatsky Rise, it formed on virtually zero thickness lithosphere, so it’s in isostatic balance,” Sager said. “It’s basically floating all the time, so the bulk of Tamu Massif is down in the mantle. The Hawaiian volcanoes erupted onto thick lithosphere, so it’s like they have a raft to hold on to. They get up on top and push it down. And with Olympus Mons, it’s like it formed on a two-by-four.”

Sager and his colleagues have studied Shatsky Rise for decades, seeking to solve the puzzle of oceanic plateaus. About 20 years ago, they named Tamu Massif after Texas A&M University, Sager’s former employer, he said.

Time on such research vessels is expensive and this report is first of its kind looking at large underwater volcanoes. Much of Earth’s ocean floor remains to be thoroughly explored. This makes Sager believe that there may be even bigger volcanoes out there.

The other side of the finding:

It is easy to jump onto that startling and sexy BIG FINDING, especially something like “largest volcano on Earth” but as with almost all BIG FINDINGS in science, more work needs to be done before we can hand the medal over to Tamu Massif.

Read more at:: http://www.wired.com/wiredscience/2013/09/largest-volcano-on-earth-it-is-all-about-timing/

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