The 12 km wide and about 175 m deep El'gygytgyn crater lake in Central Chukotka, NE Siberia, is of special interest for investigation as it could provide the first undisturbed 3.6 Ma terrestrial record from the Arctic realm, reaching back a million years before the first major glaciation of the Northern Hemisphere. A single-channel seismic survey was carried out on an expedition to the lake in 2000, in which both high resolution and deep penetration data were acquired. Seismic data suggest an impact crater structure in Cretaceous volcanic bedrock, indicated by velocities of >5000 m s-1, whose upper 500-600 m is brecciated. The lake is filled with two units of sediments, the upper one well stratified and the lower one massive. In the center of the lake, the combined thickness of the two sedimentary units is estimated to be 320-350 m. The upper unit is draped over the location of an interpreted central peak and is locally intercalated with debris flows, mainly in the western part of the lake and at the lake margins. Most of the lower unit is obscured by multiples as a result of high reflection coefficients in the upper unit. As at least the upper unit appears to be undisturbed by glaciation, the lake should yields unique information on the paleoclimatic development of the East Siberian Arctic. © 2006 Springer Science+Business Media B.V.