The impact of cosmic bodies to produce large impact craters is related with the propagation of seismic waves which may release energies comparable to strongest earthquakes, and even beyond that. It is obvious that similar processes and well-known drastic deformations may result in the ground and at the earth’s surface.
In this context, W. Alvarez and coauthors (Alvarez W., Staley E., O’Connor D., Chan M.A., Synsedimentary deformation in the Jurassic of south-eastern Utah, a case of impact shaking? Geology, 1998, 26, 579-582) went into an interesting question when they related characteristic deformations in exposed older geological layers with a possible meteorite impact in a past geologic epoch thus pointing to the Upheaval Dome impact structure (Utah, USA) and distant rock liquefaction phenomena. Rock liquefaction is an established process during strong earthquakes which can lead to enormous modifications of the earth’s surface and catastrophic damage when the seismic shock affects water-saturated uncemented rocks. For the study of earlier earthquakes in the geologic past (paleoseismicity), observations in older layers may be important, and Alvarez had now pointed to the possibility that fossil sedimentary liquefaction features need not necessarily have originated from earthquakes but may be related with former large impact events. A critical debate, however, submitted that in the special case such a context of the relatively small 6 km-diameter Upheaval Dome impact structure and the geological outcrop some 260 km apart must be questioned.
Now for the first time, a compelling direct evidence for the relation of a large meteorite impact with distinct rock liquefaction features has been established. The recently printed article
Ernstson, K., Mayer W., Neumair, A., and Sudhaus, D. (2011): The sinkhole enigma in the alpine foreland, Southeast Germany: Evidence of impact-induced rock liquefaction processes. – Cent. Eur. J. Geosci., 3(4), 385-397. DOI: 10.2478/s13533-011-0038-y
describes the first geologic and geophysical investigations of the so-called “Thunderhole” (in German: Donnerloch) phenomenon in the region of the town of Kienberg north of Lake Chiemsee in Southeast Bavaria (Germany).
Fig. 1. A freshly caved-in and a somewhat older thunderhole near the town of Kienberg north of Lake Chiemsee. Strikingly different from customary and well known sink holes e.g. in karst areas, the thunderholes exhibit a highly energetic rock mass transport from the bottom up before collapse, which is typical for liquefaction processes.
The authors conclude that the innumerable enigmatic sudden sinkhole cave-ins having happened in living memory originate from late and even today acting processes of an earlier shock-induced underground rock liquefaction known from strong earthquake shocks. The geologically prominent underground structures that have now been uncovered are considered the result of impact shocks in the course of the formation of the Chiemgau meteorite crater strewn field (Chiemgau impact), and a comparison is made with the famous widespread and strong rock liquefaction features in the large region affected by the catastrophic 1811/1812 New Madrid (Missouri) earthquake series.
More detailed information about the geophysical measurements (resistivity and induced polarization (IP) soundings) of the thunderhole structures was given in a presentation at the 2011 Fall Meeting of the American Geophysical Union (AGU) in San Francisco:
Kord Ernstson & Andreas Neumair: Geoelectric Complex Resistivity Measurements of Soil Liquefaction Features in Quaternary Sediments of the Alpine Foreland, Germany. – AGU Fall Meeting, December 5-9, 2011, NS23A-1555.
Fig. 2. From the geophysical investigation of the impact-induced thunderholes in the Chiemgau impact event. The geoelectrical measurements of induced polarization on a profile across an active depression as a precursor of a future thunderhole reveal perfectly clear the intrusion paths bottom up as a document of impact liquefaction.