GEOTECHNOLOGIEN in focus

Continents: Submarine landslide with consequences ...

Wassersch pfer FS Sun / BGR
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September 2003 off the west coast of Nicaragua: sun, sea and blue sky - an idyll. But the group of German scientists aboard the research vessel Sonne has no view, they look into the depths.

For the group of researchers from various research institutes, including the GEOMAR and the University of Kiel, Professor Erwin Süss has an ambitious goal: to air one of the still-existing secrets of the continent of Central America, the origin of the fresh water streams that seem to swell up in the sea.

Off the coast of Central America, the oceanic Cocos plate slides from the west under the base of the continent. In this subduction, rock material is melted and transformed in depth. On the surface, this tremendous upheaval is noticeable, among other things, by recurrent earthquakes and volcanic eruptions. But submarine mud volcanoes, vents and the formation of methane-rich deposits are evidence of abundant activity in the underground.

But recent research has shown that the effects are by no means confined to local conditions: on the contrary, the released substances probably have a decisive influence on the entire global climate and material cycle system. In what form and to what extent this happens, the scientists want to find out on board the Sun as part of the project "Subduction - Volatile Fluids Hazards".

Active cones on the seabed

With the aid of special drills, camera-mounted grippers and a wide variety of sample collectors, they are pushing the ground to the bone. At the center of her interest are the "mounds", cone-shaped structures on the seabed, where special activity is registered and several submarine landslides, the cause of which still could not be clarified clearly. display

Close up of a human ear © Ildar Sagdejev (Specious)

And the three-week expedition succeeds: The researchers discover strange "bubble stones", where mineral-rich water rises from the pore spaces of the subsoil, and exhibit similar activity on the "mounds" as well. Interestingly, the rising water is by no means salty, but rather sweet: it contains about one-third less salt than the surrounding seawater. At the same time, however, some of the Mounds continue to lose seawater in the subsurface, keeping the underground water and material cycle going.

Sensation under the landslide

Quite surprisingly, the researchers awaited their second stop, the Quepos slide. At a depth of around 600 meters, the sediment has given way here in several places and has slid down the continental slope. In search of the cause of this geological underwater disaster, the scientists discovered high concentrations of methane in the overlying water layers an indication that probably a sudden outgassing of gas hydrates has triggered the landslides might.

Three-dimensional scanning force microscopy image of a blood clot from tzi's back wound Marek Janko

But the actual sensation was revealed when the scientists examined an area with a particularly large number of bacterial mats with the aid of the "multicorer" and soil water creatures, which were equipped with cameras. Pure blood emerges beneath the meter-thick sediment heap at the foot of the landslide S wasser out. An analysis of the trace elements quickly shows that groundwater and not "normal" deep water are actually leaking out here. Obviously there is an underground water connection to the coast, at least 80 kilometers away.

The discovery also explains why bacteria and other sea creatures are particularly abundant at this point. This seepage stream offers them particularly favorable living conditions. The researchers also come closer to the cause of the landslides: Obviously, the groundwater discharge has destabilized the gas hydrate that occurs underground and thus triggered the outbreak of gas.

Meanwhile, the scientists of the Sun Expedition are back home long ago, but the samples and data collected during the expedition are far from fully evaluated. The results so far, however, already show how much there is still to be discovered at these interfaces of the earth and how much research is still needed in this area. Research programs such as GEOTECHNOLOGIEN should help to keep the numerous secrets of the continental countries still alive ...

More about the project "Subduction" can be found here .

More information about the research of continental countries and the research program GEOTECHNOLOGIEN can be found here in go.de.

(SFB574, GEOMAR, 16.02.2004 - NPO)