OXFORD, England, Dec. 6 (UPI) -- Images from Pacific Ocean waters 4 miles deep reveal one of Earth's most violent processes as massive underwater mountains are destroyed, researchers said.
The pictures, created by sonar, reveal how tectonic action is dragging giant volcanoes into a chasm in the seabed, a highly active fault line running north from New Zealand toward Tonga and Samoa.
The volcanoes are strung across several thousand miles of ocean floor, moving westward on the Pacific tectonic plate at more than 2 inches per year, the BBC reported Tuesday.
Where the plate collides with the Indo-Australian plate, it is forced downward into the trench in a subduction zone and the volcanoes are carried with it, researchers at the University of Oxford and the University of Durham said.
The 7-mile deep trench is the second-deepest stretch of seabed in the world and could easily hold Mount Everest, the world's highest above-water mountain, researchers said.
In one of the sonar images the volcano nearest the edge of the abyss, which will be the next destroyed, is already seen starting to collapse.
Surprisingly, researchers said, earthquakes are less frequent at the exact point where the volcanoes are swallowed by the trench.
"When you see size of these features you'd think they'd cause massive earthquakes and disruption -- and that was our starting hypothesis," Oxford researcher Tony Watts said.
"But we found that the volcanoes were highly fractured before they entered the trench -- which is very important for what happens after they enter the system."
Just what does happen is still unknown, he said.
"Are they added to the Australian plate or are they carried down in fragments into the deep earth mantle?"