It comprises a single, immense, rounded dome in the shape of a shield, formed of hardened lava from an eruption around 144 million years ago.
It covers around 310,000 square kilometres (119,000 square miles) - the equivalent area of Britain and Ireland combined - and slopes upwards to a height of around 3.5km above the sea floor.
'Tamu Massif is the largest known single, central volcano in the world,' the team reported in the journal Nature Geoscience.
In area, 'it is ... approximately the same as the British Isles or Olympus Mons on Mars, which is considered the largest volcano in the Solar System.'
It adds: 'Although Olympus Mons seems to be a giant because it is more than 20km in height, its volume is only around 25 per cent larger.'
Olympus Mons, in addition, has relatively shallow roots, whereas Tamu Massif delves some 30km into Earth's crust.
Ocean surveyors had until now surmised Tamu Massif to be a vast system of multiple volcanoes, a kind that exists in about a dozen locations around the planet.
|Apr 17||Contaminated water leaks from container at Fukushima plant|
|Just over one ton of water contaminated with radioactive particulates leaked from one of the containment vessels at the stricken Fukushima Daiichi nuclear plant on Wednesday, Tokyo Electric Power Co (TEPCO) said. (Japan Today )|
|Apr 17||Japan to secure minimum required power supply capacity in summer|
|Japan is expected to secure the minimum required power supply capacity when electricity demand peaks in August, even if all the country's nuclear reactors remain offline, estimates by major regional utilities showed Thursday. (Kyodo )|
|Apr 17||Bridgestone executive to plead guilty in price-fixing case|
|A former Bridgestone Corp. (5108) executive agreed to plead guilty to conspiring to fix prices for auto parts, a day after a grand jury indicted another executive and two former workers at the Japanese tire maker. (Bloomberg )|
|Apr 17||Tokyo Station platform roof to be replaced|
|The entire roof of a JR Tokyo Station platform will be removed and replaced for first time since the station opened in 1914, according to East Japan Railway Co. (The Japan News )|
|Apr 16||Population declines for 3rd straight year|
|The nation's population has slipped for the third straight year to a 13-year low, the Internal Affairs and Communications Ministry said Tuesday. (The Japan News )|
|Apr 17||Man in his 30s being questioned over murder of 7-year-old girl in 2005|
|Tochigi prefectural police said Thursday that they are questioning a man in his 30s over the murder of a 7-year-old girl in December 2005. Japanese media quoted police as saying that the man, who was arrested for dealing in fake brand-name goods, has hinted at his involvement in the murder. (Japan Today )|
|Apr 17||6-year-old boy dead, 3-year-old girl in coma after being swept away in river|
|A 6-year-old boy died and a 3-year-old girl remains in a coma after they were swept away by a strong current in a river in Koriyama, Fukushima Prefecture, on Wednesday afternoon. (Japan Today )|
|Apr 17||Spectacular snow walls|
|People enjoy viewing the 15-meter snow walls of the Yuki no Otani (Great Snow Valley), along the Tateyama Kurobe Alpine Route that passes through the Northern Japan Alps to link Toyama and Nagano prefectures. (The Japan News )|
|Apr 17||24-year-old man arrested for robbing convenience store|
|Police in Tokyo said Wednesday they have arrested an unemployed 24-year-old man for robbing a convenience store in Shibuya. (Japan Today )|
|Apr 16||Anne Frank vandalism suspect to face psychiatric test|
|Tokyo prosecutors plan to look into whether a man, who has been arrested for allegedly vandalizing copies of Anne Frank's diary, is mentally competent to be held criminally responsible for his actions, informed sources said Wednesday. (Jiji Press )|
|Apr 16||Young salmon released into river in Fukushima|
|Fishermen in Fukushima Prefecture have released young salmon into a local river for the first time in 4 years. (NHK )|
|Apr 15||Hakamada makes first public appearance as reprieve pends|
|Apparently perplexed but thrilled to find himself in the spotlight, Iwao Hakamada, formerly the world's longest-serving death-row inmate, made his first public appearance Monday in Tokyo since being released from prison and hospitalized. (Japan Times )|
|Apr 15||Spring festival in Takayama starts|
|The Takayama Spring Festival in central Japan kicked off on Monday with its traditional float parade. (NHK )|
|Apr 15||3 family members, one relative found dead in Aichi|
|Aichi prefectural police are investigating a possible link between the discovery of the bodies of a husband and wife and their eldest son, and the body of a male relative of the deceased family who was found hanging by his neck in a hotel. (Japan Today )|
|Apr 14||Taiwanese tourists hurt in deer rampage at Nikko|
|Visitors to one of Japan's most celebrated spots are being warned to be on the lookout, after two Taiwanese tourists were injured in a rampage by a wild deer. (Japan Today )|