Christian Koeberl, head of the Department of Lithospheric Studies at the University of Vienna (Austria), has recently returned from an expedition to Arctic Siberia. He is one of the principal investigators of a drilling project at the El’gygytgyn meteorite impact crater that is coordinated by the International Continental Scientific Drilling Program (ICDP) and that was recently concluded.
The main goals of the project are to obtain, from analyses of the drill cores, new information about the formation of the impact crater, as well as to derive a climate history of the Arctic. The investigation of the impact breccia drill cores will be coordinated by Christian Koeberl, and studies in Vienna will be funded by the Austrian Science Foundation FWF.
The El’gygytgyn crater formed 3.6 million years ago by the impact of a large meteorite or asteroid, about 1 km in diameter. The crater and the lake that fills most of it are of scientific interest for two main reasons. First, this is the only known meteorite impact crater that formed in acid volcanic rocks and thus it offers the unique possibility to study the impact and shock effects on such rocks, which has implications for comparative planetology.
Second, the about 300 meter thick deposit of lake sediments that were laid down on top of the impactites constitutes a unique climate archive of the largely unknown Arctic climate history. Investigating the lake sediment drill cores will provide important constraints on cause and effect of climate changes in the polar regions. Such work has great implications for the understanding of future climate change.
Impact breccia provide important data on crater formation
The logistically very challenging drilling project was successfully concluded during the first half of May 2009. As hoped for and anticipated, an almost complete section of impact breccias was recovered underneath the lake sediments. Immediately below the lake sediments is an about 60 meter thick layer of so-called suevites. These are breccias that contain impact glasses and are composed of fragments representing a variety of different rocks that are cemented together in a fine-grained Matrix. Such rocks occur on Earth only in meteorite impact craters. Underneath the suevites, the drilling encountered broken and fractures volcanic basement rocks, which were shocked, brecciated, and uplifted during the impact event.
During formation of a meteorite crater, basement rocks are first pushed downwards, but then rebound and formerly deep-lying rocks are uplifted to close to the surface and form a so-called central peak. Impact craters with a central peak are also called “complex craters”. Ther formation of such a crater, and the central peak, is a very rapid process – within a minute so so, a mountain of several kilometers in diameter is uplifted out of the ground by 1 to 2 kilometers! The over 200 meters of impactite drill cores that were recovered will help to understand the details of the crater formation process. In total the drilling reached a depth of 517.3 meters below the lake floor, or a total depth, from the lake surface, of 687.3 meters.
Breccias will be studied at the University of Vienna during the next years
In June 2009 the drill cores will be transported by charter plane from Pevek (at the Arctic Ocean, in the northeast corner of Russia) to St. Petersburg. There the export and customs procedures take place and the cores are then expected to be transported to Germany in September or October 2009, from where the next steps of investigations will be coordinated. The main parts of the studies will take several years. The impact breccia studies will be coordinated by the Austrian impact researcher Christian Koeberl, at whose laboratory major aspects of this work will be done within a research project that was recently funded by the Austrian Science Foundation FWF. Besides a detailed study of the shock behavior of the volcanic basement rocks, his group will attempt to determine the composition and nature of the meteorite that formed the crater. In addition, it is hoped that the studies will allow constraining the energy that was released during the impact, which in turn has implications for the environmental effects of the impact event.
Complex preparations with great financial effort
On April 14, 2009, at a depth of about 312 meters below the lake floor (total depth 482 meters) the drilling reached the transition zones between the post-impact lake sediments and the impact breccia deposits. This also represented the time marker of 3.6 million years. This important moment was preceded by a long and difficult process. Just the planning of this project, from the scientific concept to the logistical planning, application for funding, and obtaining all the necessary permits, took over 8 years. Several hundred tons of equipment had to be transported to the very remote drilling location. Drilling was done from the top of the frozen lake, where it turned out, for example, that the actual ice sheet had to be strengthened by pumping more water to the surface where it froze to increase the ice thickness, so that the about 75-ton drilling platform and all the supporting vehicles were safe above the 170-meter-deep lake.
The closes town is Pevek at the Arctic Ocean, at a distance of about 350 km from the drilling location. In Pevek is a port (ice-free only for a few months in the summer) and an airport, which is connected to Moscow by only one flight every two weeks. The complete drilling equipment was sent by ship to Pevek during the summer of 2008 and then transported over land, on a specially constructed snow road, to the El’gygytgyn lake. Personnel and scientists, as well as sensitive equipment, were transported to the lake by cargo helicopter – and each of the about 15 flights cost about 13,000 Euro. Temperatures down to -30°C and snow storms with up to 100 km/h, resulting in wind-chill factors of -50°C, made the work difficult at times.
In total the drilling costs alone were about 10 million US dollars. This does not yet include the actual scientific studies on the drill cores that will now follow. The drilling costs were mainly financed by the ICDP, the US National Science Foundation, and the German Ministry for Education and Research. The Austrian Ministry of Science and Research also provided a contribution. The other principal investigators and project leaders are Prof. Julie Brigham-Grette (University of Massachusetts-Amherst, USA), Prof. Martin Melles (UNiv. Cologne, Germany), and Dr. Pavel Minyuk (Russian Academy of Sciences, Magadan, Russian Federation).
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