Rise and fall of underwater volcano revealedhttp://www.bbc.co.uk/news/science-environment-18040658
13 May 2012 Last updated at 13:14 ET
The images, gathered by sonar from a research ship, shed new light on the turbulent fate of submarine mountains.
Published in the journal Nature Geoscience, the findings were made during a seabed survey last year.
Lead author Tony Watts of Oxford University told the BBC that the revelation was "a wake-up call that the sea-floor may be more dynamic than we previously thought."
"I've spent my career studying the seabed and have generally thought it pretty stable so it's stunning to see so much change in such a short space of time."
As many as 32,000 underwater mountains have been identified around the world and the majority are believed to be volcanic in origin. Several thousand of these may be active but a combination of ocean depth and remoteness means that very few have been studied.
This research into the Monowai volcano provides a fascinating insight into the little-known world of submarine geology.
Monowai was first spotted from an aircraft in 1944. Surveys over following years found evidence of significant change - with the sea discoloured and seismic activity detected. Studies between 1978 and 2007 showed the summit repeatedly rising and falling
But this latest analysis compared images gathered on May 14 and then June 1-2 last year and even in that short period the volcano had undergone a transformation.
Travelling on the research ship the R/V Sonne, the scientists first spotted that the sea above the volcano had turned a yellowy-green and gas bubbles were rising to the surface.
According to Professor Watts, ""I had butterflies. The gas was smelling awful - like rotten eggs. We saw a slick ahead of us and with something venting, there could have been a sudden shallowing of the water."
The team then left the area to carry on with planned research elsewhere but three days later were warned that seismic detectors on the Cook Islands had detected violent activity around the volcano over a five-day period.
"If we had been over the volcano during the eruption, rocks could have hit the hull of the ship - that could have been potentially dangerous."
Later the ship returned to the scene and the scientists were surprised to see how much the volcano had changed. In the space of a fortnight, one part of the volcano's summit had collapsed by as much as 18.8m while new lava flows had raised another area by 79.1m. Most striking was the creation of an entirely new volcanic cone.
The researchers believe the changes are larger than at most other volcanoes. Only Vesuvius and Mount St Helens have recorded larger growth rates.
The paper says the speed of growth and change is "a reminder of how rapidly geological processes such as submarine landsliding and volcanism can occur."
Professor Watts said: "Any movement on the seabed has the potential to create a tsunami. An earthquake suddenly dislocates the seabed. Here a violent disturbance lasted five days with magma oozing out which might be too slow to trigger a tsunami - but it's unknown.
"This is a violent exchange of rock into the water - it could destabilise the cone and cause a landslide which in principle could cause a tsunami.
The same expedition's survey produced stunning images last year of a line of underwater volcanoes being carried inexorably to the chasm of a subduction zone, the Tonga Trench.
That research was investigating whether the volcanoes exacerbated or dampened the pressures on the fault line.
6 December 2011 Last updated at 12:18 ET
Undersea mountains march into the abyss
They expose how tectonic action is dragging giant volcanoes into a chasm in the seabed.
The volcanoes are strung across several thousand kilometres of ocean floor and are moving westward on the Pacific tectonic plate at up to 6cm per year.
The extraordinary scene was captured along the Tonga Trench during a research expedition last summer.
The trench is a highly active fault line running north from New Zealand towards Tonga and Samoa.
The first images have been released to BBC News as the findings are presented to the annual conference of the American Geophysical Union.
They are the result of a joint project by the universities of Oxford and Durham, funded by the Natural Environment Research Council.
Into the abyss
Where the Pacific plate collides with the Indo-Australian plate, it is forced downwards into the trench, a subduction zone, and the volcanoes are carried with it.
The trench, reaching a depth of 10.9km, forms the second deepest stretch of seabed anywhere in the world - easily large enough to hold Mount Everest.
One image shows the volcano nearest the edge of the abyss - the next to be destroyed - already starting to collapse.
With frequent earthquakes, the region is vulnerable to tsunamis and one aim of the research is to understand whether the destruction of the volcanoes adds to the risk.
One theory is that the volcanoes add friction to the movement of the two plates which leads to a greater build-up of tension and consequently to a more explosive quake.
Another is that by shearing into blocks as they collapse, the volcanoes provide a kind of buffer easing the subduction process.
Professor Tony Watts of Oxford University, joint leader of the project, says that earthquakes are less frequent at the precise point where the volcanoes enter the trench.
"When you see the size of these features you'd think they'd cause massive earthquakes and disruption - and that was our starting hypothesis."
"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.
Analysis so far has not determined the precise impact of this process.
Professor Watts says the key question still isn't settled: "Are they added to the Australian plate or are they carried down in fragments into the deep earth mantle?"
10 August 2012 Last updated at 09:15 ET
Vast volcanic 'raft' found in Pacific, near New Zealand
The unusual phenomenon was probably the result of pumice being released from an underwater volcano, experts said.
One navy officer described it as the "weirdest thing" he had seen at sea.
Lieutenant Tim Oscar told the AFP news agency: "As far ahead as I could observe was a raft of pumice moving up and down with the swell.
"The [top of the] rock looked to be sitting two feet above the surface of the waves and lit up a brilliant white colour. It looked exactly like the edge of an ice shelf," the officer said.
Researchers aboard the ship, HMNZS Canterbury, suggest that the source of the pumice was an underwater volcano (seamount) known as Monowai, located to the north of New Zealand.
The pumice is likely to have been formed when lava from the seamount came into contact with seawater, and as it is less dense than water it quickly rises to the surface of the ocean.
--This all goes to show several things pertinent to the story of Atlantis. The first is that volcanic areas under the sea can increase or decrease their altitude by kilometers in a mere matter of weeks, ansd it is possible for mountains undersea to "Fall down a crack in the sea floor" to be destroyed without a trace. Furthermore it demonstrates the huge area covered by pumice in case of such an erruption which Plato referred to as a "Sea of mud". the traces of the decayed pumice raft at the end of the ice age are a known stratum on the North Atlantic floor: it reaches from North America clear across to Europe. At one time virtually the whole of the North Atlantic must have been covered with Pumice, and Otto Muck makes note of the fact.
Best Wishes, Dale D.