Lake El’gygytgyn – a 3.6 million years old meteorite impact crater lake in NE Siberia
The El’gygytgyn crater (diameter 18 km) located in the remote Anadyr Mountains in Central Chukotka, NE Siberia (Figure 1), was formed by a meteorite impact about 3.6 Mio years ago and is now one of the world’s best preserved impact craters of its size. The crater has never been glaciated since its formation and, therefore, its lacustrine fill provides up to 3.6 Mio years of Arctic paleoclimate history. The crater lake has a diameter of about 12 km and is bowl-shaped with a maximum depth of about 170 m. It is fed by 50 inlets and drained by a single outlet in the southern part. The crater rim forms the outer margin of the lake’s catchment.
In a first step towards continental deep drilling (ICDP) a seismic refraction and reflection pre-site survey was carried out during expeditions in 2000 and 2003.
The seismic reflection and refraction data in combination with the echosounder (3.5 kHz) data allowed a first study on the characteristics of the lacustrine sediments and on the crater geometry (Figure 2). The lake revealed about 400 m of lacustrine sediment, underlain by an impact breccia and brecciated bedrock. The crater morphology shows a central uplift ring structure as expected for impact craters of comparable size.
Debris flows are prominent features in the 3.5 kHz profiles, and debris flows with several meters in thickness can even be observed in the reflection seismic sections. Debris flows seem to occur cyclically in distinct levels of the lacustrine sediments. Within these levels, several debris flows can be observed in different regions of the lake, mainly in proximal areas. The lake and its sediments are highly sensitive to changes in insolation and atmospheric conditions, thus it is likely that the occurrence of debris flows is closely correlated with paleoclimate changes. Thawing of permafrost soil during warmer periods most probably led to thicker active layers and hang instabilities in the catchment and, subsequently, to enhanced mass movements such as lacustrine debris flows. However, little is known about land-lake interactions at the Lake El’gygytgyn so far, and it is not yet clear whether these debris flows are in fact robustly correlated to warmer periods.
At present, a three-dimensional model of the lacustrine sediments will be developed based on seismic reflection and high-resolution 3.5 kHz profiles. This model will be the first three-dimensional record from the impact crater lake compared to punctual information from cores and to two-dimensional seismic sections. It will allow us to better understand sedimentary effects due to paleoclimate changes. Furthermore, a detailed correlation between the future ICDP cores will be possible by mapping reflectors between the drillsites.