Chiemgau impact: an article on the impact-induced soil liquefaction (rock liquefaction)

Article on the Thunderhole phenomenon in the Chiemgau impact area: 

The sinkhole enigma in the alpine foreland, Southeast Germany: Evidence of impact-induced rock liquefaction processes

Kord Ernstson, Werner Mayer, Andreas Neumair and Dirk Sudhaus


The article describes the very first geologic and geophysical investigations of the so-called Thunderhole (“Donnerloch“) phenomenon in the region of the small town of Kienberg north of Lake Chiemsee in Southeast Bavaria. 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).

Some characteristic images of this highlighting rock liquefaction (or soil liquefaction) process can be seen on continuing

freshly collapsed sinkhole impact-induced soil liquefaction chiemgau impact

A freshly collapsed sinkhole (Thunderhole) – from the impact-induced rock liquefaction (soil liquefaction) in the Kienberg district. Chiemgau impact.

excavator geologic excavation of an impact-induced sinkhole Thunderhole Chiemgau impact

Beginning the excavation of a sealed sinkhole – impact induced soil (rock) liquefaction in the Chiemgau impact event.

impact-induced sinkhole before excavation Chiemgau impact

A sealed sinkhole before excavation. Kienberg district, area of the impact-induced sinkhole phenomenon; Chiemgau impact event.

shock-induced perforation of a Nagelfluh plate as a result of explosive discharge in the course of the Chiemgau impact event

The excavated sinkhole #1 exhibiting the perforated Nagelfluh plate. Nagelfluh denotes a strongly cemented, concrete-like conglomerate. The perforation has been the result of  shock-induced rock (soil) liquefaction and explosive discharge upwards. The white color   originates from scratches of the excavator that was unable to penetrate the Nagelfluh plate.

highly energetic intrusion and uplift in the rock liquefaction process Chiemgau impact

Geological excavation of sinkhole #1 demonstrating the heavy shock from below. a = Nagelfluh perforation; b = intrusion of sandy-gravelly material; c= updoming of the overburden. Rock (soil) liquefaction in the Chiemgau impact event.

heavily fractured cobbles as a result of highly energetic soil liquefaction intrusion Chiemgau impact

Strongly fractured cobbles sampled from the top of the intrusion within soft sediments prove a sudden highly energetic event. Rock (soil) liquefaction in the Chiemgau impact event.

geological excavation of sinkhole (Thunderhole) #2 showing breccia intrusion into loess cap

Geologic excavation of sinkhole #2 in the Kienberg district.Rock (soil) liquefaction in the Chiemgau impact event. Note the breccia-like intrusions (dark) into the loess top layers. Rock (soil) liquefaction in the Chiemgau impact event.

sinkhole #2 excavation collapse structure Chiemgau impact soil liquefaction

Excavation wall, sinkhole #2, with collaps structure. Rock (soil) liquefaction in the Chiemgau impact event.

open holes encountered in excavation #2 soil liquefaction Chiemgau impact

Open holes uncovered by the sinkhole excavation: “embryo” of a future thunderhole collapse. Rock (soil) liquefaction in the Chiemgau impact event.

heavy nagelfluh blocks (up to several 100 kg) uplifted up to 1 m in the Chiemgau impact soil liquefaction process

Nagelfluh blocks weighting up to several 100 kg that were uplifted up to 1 m by the shock-induced rock liquefaction discharge. Rock (soil) liquefaction in the Chiemgau impact event.

Google Earth image Mörn farmhouse soil liquefaction phenomena, active depression, possible sand boils

Mörn farmhouse near Kienberg. a = location of an active depression probably preceding a coming Thunderhole collapse. Here, geophysical measurements (complex geoelectrics, resistivity and induced polarization electrical imaging) have been performed. b: According to the owners of the Mörn farmhouse this pool originally consisted of two circular small basins. We suspect that they were related also with the Chiemgau impact rock liquefaction and originated from an explosive discharge (sand explosion, sand boil) well known to occur with very strong earthquakes (e.g. with the 1811/1812 New Madrid earthquake in the USA).

complex resitivty measurements elctrical imaging over an active rock liquefaction depression, Chiemgau impact

Geoelectric field campaign. Electric imaging (resistivity and induced Polarization, IP) over   the active depression near the Mörn farmhouse. Instrument Lippmann 4point light high power für spectral IP measurements.

resistivity and induced polarization pseudosections, electrical imaging of the active rock liquefaction depression, Chiemgau impact

Electrical imaging profile over the active depression at the Mörn farmhouse. Resistivity and Induced Polarization (IP) pseudosections. Note the clear signature of the intrusions from below seen in the IP section. In many cases IP proves to supply a much better resolution of underground structures compared with resistivity.