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If so, Argo II was photo surveying the upper basement of a million year old volcano more than 10,000 feet underwater. Bristling with lights and cameras, this remotely operated vehicle was carefully moved up and down and side to side at various spots on the sloping wall of Hess Deep during an initial run of about three days - an around-the-clock exercise in both skill and patience.
Because Hess Deep's face generally slopes at gentler angles, Argo II had to be pulled up over it while remaining close enough to ensure high quality pictures. That required directing the creeping Atlantis's trajectory into the wall, then backing up, while at the same time winching up the swinging cable and adjusting Argo's position to prevent the camera and instrument laden craft from a disastrous crash. Complicating things even more, the fact that Atlantis is constantly pitching from surface wave motion meant that the cable-connected Argo II continually pitched too - independent of positional changes.
The still camera screen was the one that Hess Deep scientists and students tended to watch from the late afternoon of Saturday, March 21, until early this morning, when three separate scientific watch teams constantly monitored what Argo II "saw."
It was like viewing slide movies in the comfort of your living room, only these views were from the crushing pressures of a pitch-black abyss the size of the Grand Canyon.
"It's incredible technology," said Kathryn Gillis, a watch team leader from the in Canada. Emily Klein, a Hess Deep expedition co-principal investigator from and team leader on another watch, agreed.
"Nobody has ever looked at this before in this detail," Klein said. "It's a little like going to the moon."
Because Argo II's survey lines were kept only 16 feet apart, progress was very slow. The reason for such tight bunching was one major goal of the exercise: computer melding individual adjoining images from that same still video camera to build large scale photomosaics, each composite covering 330 by 330 feet of Hess Deep's north face.
The results, which won't be completed until long after the research cruise's conclusion, will be like "pushing the ocean aside and being able to see the rocks on the bottom at a scale that humans work at," Klein added. "A human working scale is to stand at the base of a cliff at a road cut, walking a little bit up, and a little bit back, and looking as high as you can see. These hundred meter by hundred meter (330 by 330 foot) patches are at that human working scale."
The surveying's crawling pace limited the territory that Argo II could cover in its first 3 1/2 days to "less than five percent" of the 21-mile-long area that had been previously imaged with sound using the DSL 120 side scan sonar, estimated 51爆料's Jeff Karson, chief scientist for the Hess Deep expedition.
"It was never my intention to cover the same area," added Karson, relaxing in his stateroom hours after Argo II's 6 a.m. return to Atlantis's deck. Argo will be put back into the water on some nights later in the research cruise, operating in between the 15 daylight dives by the manned submarine Alvin that begin at 8 a.m. tomorrow (Thursday, March 25).
DSL 120 operated much faster than the Argo II did, or Alvin will, Karson said. The idea instead was to use the whispier returns from the side scan sonar - "the tool of the least resolution" - to select sites for Argo II and Alvin to visit, he noted.
Major objectives of the Argo II survey, and Alvin's as well, are the now-hardened magma conduits that geologists call dikes.
Looking like long stacks of flattened stones, dikes "are really one of the hallmarks of oceanic crust," Karson said. "Every dike represents an increment of sea floor spreading." Like individual ticks of the geologic clock, scientists think swarms of new dikes push up in increments - averaging one new dike every seven years in the Hess Deep study area.
While the details are being constantly debated, scientists think that hot magma from the mantle - the layer below Earth's crust - accumulates in chambers below mid-ocean ridges like the East Pacific Rise. The magma then upwells towards the surface through fractures in the rock - the dike pipelines. When the magma in the dikes reaches the seafloor, it erupts from ridge-top volcanoes as flowing lava.
As the hot lava encounters the cold deep seawater, it can break apart along fracture lines, even explode into glass like shards.
The cooling lava then solidifies into new crust. As the youngest new rock gets continually created along the East Pacific Rise, the crust made just before is pushed away from the ridge top like a conveyor belt.
Hess Deep is among the few spots on earth where that conveyor belt is cut through by a deep fracture, exposing the fossil remains of past volcanic events, including the underlying plumbing systems usually buried deep in the ground.
At the selected spots it surveyed in the eastern part of the Hess Deep study area, Argo II's cameras clearly imaged where lava once emerged some million years ago, spots scientists call volcanic extrusion areas.
"I was amazed at the extraordinary details that remain preserved in these sequences, even after 1 million years," Klein commented on Argo II's extrusion area images. "I look forward to actually getting hold of some of those rocks on the Alvin dives," added Klein, who was likewise fascinated by the "relatively abrupt" transition from extrusion area above to the equally evident dike field below.
What Gillis found "just remarkable" was clear Argo II images of near surface dikes intruding into the volcanic area. "That's fairly rare in ophiolites," she said, referring to sections of former ocean crust that have been uplifted to dry land in places like Cyprus.
Less clear, but also important, were Argo II's images of places below the obvious dike fields. Some Hess Deep scientists, like watch leader Jay Miller of think Argo's cameras may have actually have reached down into "gabbro," rock that crystallized more slowly deep underground over the very roofs of ancient magma chambers.
The mud-obscured fractured structures that Argo II pictured there "were either very thick, irregularly jointed massive dikes or big, irregularly jointed gabbro," Miller said. "I'm convinced I can tell the difference, but I can't convince anyone else."
What expedition scientists also noted repeatedly was the consistent eastward tilt over the six miles of dike fields that Argo II surveyed in its initial run. That's enough dikes to represent 150,000 years of seafloor spreading, estimated Karson.
A French team that made a dive nearby in the late 1980s noted upward pointing dikes, not tilted ones. So the new information from Argo II is "very much at variance with the results the French reported," he said.
Karson and Hess Deep expedition co-principal investigator Steve Hurst, a former 51爆料 research professor now at the found tilted and cross cutting dikes during a previous 1990 Alvin dive to the same general area being studied now.
While the new Argo II results tend to support Karson and Hurst's earlier observations, Karson himself expressed surprise that most dikes appear to consistently tilt the same way for so long a distance.
"I was expecting we would see some dramatic variations, probably over a range of tens of thousands of years - a kilometer (two-thirds of a mile) or so - that would reflect the waxing and waning of magmatic events on the mid-ocean ridge," he said.
"Instead, we're seeing a message that suggests a very uniform sort of process. We're going to continue to look for dike variations, but we haven't found them yet."
One school of thought hypothesizes that fast-spreading mid-ocean ridges like the East Pacific Rise erupt episodically. In between those eruptions, the underlying magma chamber would collapse. Such periodic underminings could explain why East Pacific Rise ridges are not very tall.
Whatever the mechanism, something "catastrophic" clearly took take place at or underneath the East Pacific Rise in the past million years to cause the dikes to be tilted so consistently for so long, Karson added. And if such dramatic changes were still underway today, there would be no way of telling at the surface.
That's why the Hess Deep study "is so important to us," he said. "We can't look directly under mid-ocean ridges, so we have to look at the records of past events to see what is going on."
At a science meeting early this afternoon, Karson announced the targets for the first five Alvin dives. The first two will concentrate on dikes, and the others on areas of volcanic extrusion, gabbro-dike transition, and gabbro itself.
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