Dellen is a 20 km diameter (topographic) impact crater formed ca 90 Ma ago in a terrestrial environment. The structure is characterised by impact melt (two outcrops) and suevite (boulders only) occurrences in the centre of a ca 350 m deep topographic depression occupied by the lakes Norra and Södra Dellen. Detailed petrophysical, gravity, airborne magnetic, electromagnetic, gamma radiation measurements were made as part of a systematic survey.
Boulders of suevite have been found 20 km away in glacifluvial deposits and boulders of characteristic impact melt (dellenite) as far away as 300 km to the south (in northern Uppland, Sweden).
An information folder (Dellenstrukturen en meteoritkrater, by Herbert Henkel) , two nature trails with descriptions (Natur och kulturstig vid Avholmsberget, and Från kraterrand till kraterbotten Geologisk naturstig i Dellenkratern, by Herbert Henkel) and a rock exhibition is available for interested tourists.
Several international courses on impact geology and geophysics have had Dellen as field example.
Presently research is ongoing about impact induced fracturing and integrated geophysical modeling of the structure.
References:
Henkel, H., 1992: Geophysical aspects of meteorite impact craters in eroded shield environment, with special emphasis on electric resistivity. Tectonophysics 216: 63-89.
Svensson, N-B., 1969: The Dellen lakes, a probable meteorite impact in central Sweden. Geologiska Föreningen i Stockholm Förhandlingar 90: 314-316.