Deep-sea robot unravels underwater mountain

Underwater vehicle ABYSS provides new insights into the breaking up of a continent

The AUV ABYSS of the IFM-GEOMAR is launched from the research vessel SONNE. With its high-precision sensors it allows new views of the seabed. © AUV-Team, IFM-GEOMAR
Read out

The successful search for the wreck of the Air France Airbus crashed in the Atlantic in 2009 has made "ABYSS" known. But now the Autonomous underwater vehicle also caused a sensation in its specialty. With the help of ABYSS, a first high-precision map of the ocean floor at the Moresby Seamount in the Eastern Pacific has been created, providing important new insights into the breaking up of a continent. The results of their new study are now presented by Kiel and Bonn geologists in the journal "Geology".

At first glance, the map looks unspectacular. It shows a 30 degree steep mountain slope with some smooth surfaces, in between, but also rougher passages and demolition edges. The special feature, however, is that the summit of the mountain is 110 meters below the water surface of the Woodlark basin in the Eastern Pacific. The foot of the Moresby seamount, the name of the mountain, is even more than 2, 800 meters deep. Until now, only maps existed that showed his slopes as completely uniform, unstructured areas.

Surveying so far only from ships

"In the past, the seamount could only be surveyed by ships whose sonar systems allow a resolution of at most 25 by 25 meters, " explains geologist Romed Speckbacher from the Kiel Leibniz Institute for Marine Sciences (IFM-GEOMAR). The new map of the Moresby Seamounts by Speckbacher and his colleagues, on the other hand, is so highly resolved that even structures only two meters by two meters in size are visible. The survey was carried out by ABYSS during an expedition with the German research vessel "Sonne" in autumn 2009. "It's as if we zoomed in on the seabed, " says Speckbacher.

Moresby Seamount deportation Romed Speckbacher

Traces of tectonic forces discovered

Thanks to the significantly higher resolution compared to previous maps, the geologists were able to spot exciting details that had hitherto remained hidden from them. It was known that there is a geological fault on the northern slope of the Moresby Seamount - the so-called "Moresby Seamount Deportation". The good resolution of the new map shows for the first time the traces of the tectonic forces along the deportation.

The scientists also discovered a second disturbance, which runs obliquely: "Both disturbances are currently active, " reports Speckbacher, and one The change in plate tectonics in the Woodlark Basin means that the newly discovered disturbance will play a more important role in the future than the already known deportation

Continental Rift Valley

In the Woodlark Basin, the earth's crust breaks slowly, but incessantly, towards the west. This is called a continental rift valley. At the resulting gap, hot material from the Earth's mantle forms basaltic melt, which solidifies into new oceanic crust.

The newly discovered fault on the Moresby Seamount matches the expansion axis of this rift fracture. Our data shows that in geologically near future the grave breach of the Woodlark Basin will also tear up the northern slope of the Moresby Seamount and continue along the new spur towards Papua New Guinea, "explains Professor Jan Behrmann, Co-author of the current study.

Water as a lubricating film

However, the AUV ABYSS has not only mapped the seafloor, but also measured unusual temperature fluctuations and water turbidity on the seafloor. We assume that pressurized water in the earth's crust acts like a lubricating film between the layers of rock, making it possible to move the disturbances first. In some areas of Moresby Seamount deportation, these waters escape from the seafloor ABYSS discovered these sites, "explains Speckbacher.

The dive of the AUV, where all this data was collected, was the longest over 20 hours that the device had accomplished. "A particular challenge was to program ABYSS so that it was able to measure the sloping slope with consistent precision, " recalls Klas Lackschewitz, who heads the AUV team at the IFM-GEOMAR. The result was worth the effort: "Thanks to the AUV, we are able to discover new worlds and to carry out structural geological field work in the deep sea in a spectacular way", emphasizes Speckbacher. (Geology, 2011; doi: 10.1130 / G31931.1)

(Leibniz Institute for Marine Sciences, 04.07.2011 - DLO)