"Long before it's in the papers"
January 27, 2015

RETURN TO THE WORLD SCIENCE HOME PAGE


Earth’s biggest volcano found to lurk under Pacific

Sept. 6, 2013
Courtesy of the University of Houston
and World Science staff

Earth’s larg­est known vol­ca­no lies un­der the Pa­cif­ic Ocean, is about the size of the Brit­ish Isles or New Mex­i­co, and is al­so one of the big­gest in the whole So­lar Sys­tem, sci­en­tists re­port.

Univers­ity of Hous­ton re­search­er Wil­liam Sag­er first be­gan stu­dy­ing the in­ac­tive vol­ca­no, dubbed the Tamu Mas­sif, about 20 years ago. New find­ings by Sag­er and his team ap­pear in the Sept. 8 is­sue of the jour­nal Na­ture Ge­o­sci­ence.

A 3-D image of the seafloor show­ing the size and shape of Ta­mu Mas­sif. (Cour­tesy U. of Hous­ton)


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 erup­tion of sev­er­al un­der­wa­ter vol­ca­noes, the sci­en­tists said.

Tamu Mas­sif is de­scribed as a shield vol­ca­no, or a broad, round­ed vol­ca­no built up by suc­ces­sive out­pour­ings of la­va. But it was pre­vi­ously un­clear wheth­er it was really one vol­ca­no, or a com­pos­ite of many erup­tion points, Sag­er and col­leagues said. Com­bin­ing sev­er­al sources of ev­i­dence, they con­clud­ed that the huge mass of bas­alt com­pris­ing the struc­ture did in­deed erupt from a sin­gle source near the mid­dle.

“An im­mense amount of mag­ma [mol­ten rock that pours out as la­va] came from the cen­ter, and this mag­ma had to have come from the Earth’s man­tle,” Sag­er said. “So this is im­por­tant in­forma­t­ion for ge­ol­o­gists try­ing to un­der­stand how the Earth’s in­te­ri­or works.”

There may be larg­er vol­ca­noes, he added, “but we don’t know if these fea­tures are one vol­ca­no or com­plexes” of them.

Tamu Mas­sif is al­so un­usu­ally low and broad, mean­ing that the erupted la­va flows must have trav­eled long dis­tances, the in­ves­ti­ga­tors said. The seafloor is dot­ted with thou­sands of un­der­wa­ter vol­ca­noes, or sea­mounts, most of which are smaller and steep­er.

“It’s not high, but very wide, so the flank slopes are very grad­u­al,” Sag­er said. “In fact, if you were stand­ing 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 em­a­nat­ed 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 es­ti­mat­ed 120,000 square miles (310,000 square km). Ha­waii’s Mauna Loa – Earth’s larg­est ac­tive vol­ca­no – co­vers about two per­cent of that ar­ea. To find a vol­ca­no com­pa­ra­ble in size to Tamu Mas­sif, Sag­er said, one must look to the Mar­tian vol­ca­no Olym­pus Mons, vis­i­ble on a clear night with a good back­yard tel­e­scope. It’s about 25 per­cent larg­er by vol­ume than Tamu Mas­sif.

The study re­lied on core sam­ples, which are ex­tracted chunks of Earth, and seis­mic re­flec­tion da­ta, ob­tained by di­recting vi­bra­tions into the sea­floor and mea­sur­ing their re­flect­ions. Tamu Mas­sif is be­lieved to be about 145 mil­lion years old, and to have gone in­ac­tive with­in a few mil­lion years af­ter it was formed. Its top lies about 6,500 feet be­low the ocean sur­face, while much of its base is be­lieved to be in wa­ters that are al­most four miles (a­bout 6 km) deep.


* * *

Send us a comment on this story, or send it to a friend

Sign up for
e-newsletter
   
 
subscribe
 
cancel

On Home Page         

LATEST

  • St­ar found to have lit­tle plan­ets over twice as old as our own

  • “Kind­ness curricu­lum” may bo­ost suc­cess in pre­schoolers

EXCLUSIVES

  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

Earth’s largest known volcano lies under the Pacific Ocean, is about the size of the British Isles or New Mexico, and is also one of the biggest volcanoes in the Solar System, scientists report. University of Houston researcher William Sager first began studying the inactive volcano, dubbed the Tamu Massif, about 20 years ago. New findings by Sager and his team appear in the Sept. 8 issue of the journal Nature Geoscience. 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 eruption of several underwater volcanoes, the scientists said. Tamu Massif is described as a shield volcano, or a broad, rounded volcano built up by successive outpourings of lava. But it was previously unclear whether it was really one volcano, or a composite of many eruption points, Sager and colleagues said. Combining several sources of evidence, they concluded that the huge mass of basalt comprising the structure did indeed erupt from a single source near the middle. It’s “the biggest single shield volcano ever discovered on Earth,” Sager said. There may be larger volcanoes, he added, “but we don’t know if these features are one volcano or complexes of volcanoes.” Tamu Massif is also unusually low and broad, meaning that the erupted lava flows must have traveled long distances, the investigators said. The seafloor is dotted with thousands of underwater volcanoes, or seamounts, most of which are smaller and steeper. “It’s not high, but very wide, so the flank slopes are very gradual,” Sager said. “In fact, if you were standing 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 emanated 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 estimated 120,000 square miles (310,000 square km). Hawaii’s Mauna Loa – Earth’s largest active volcano – covers about two percent of that area. To find a volcano comparable in size to Tamu Massif, Sager said, one must look to the Martian volcano Olympus Mons, visible on a clear night with a good backyard telescope. It’s about 25 percent larger by volume than Tamu Massif. The study relied on two sources of evidence: core samples collected on Integrated Ocean Drilling Program in 2009, and seismic reflection data gathered on two submarine expeditions. Tamu Massif is believed to be about 145 million years old, and to have gone inactive within a few million years after it was formed. Its top lies about 6,500 feet below the ocean surface, while much of its base is believed to be in waters that are almost four miles (about 6 km) deep. “It’s shape is different from any other sub-marine volcano found on Earth, and it’s very possible it can give us some clues about how massive volcanoes can form,” Sager said. “An immense amount of magma [molten rock that pours out as lava] came from the center, and this magma had to have come from the Earth’s mantle. So this is important information for geologists trying to understand how the Earth’s interior works.”