Pumice is a porous volcanic rock that is formed in gas-rich explosive eruptions on mixing of lava and water. When pressure releases, the melt froths by expansion of carbon dioxide and water vapor, and on rapid cooling the peculiar strongly vesicular texture forms. Pumice is nearly exclusively composed of glass with few mineral inclusions and has up to 90 % porosity which is why in general it floats in water. Depending on the source material and the texture pumice occurs in a broad color spectrum, from nearly white to yellow, gray and practically black. Well known is the Italian pumice from Lipari and Stromboli, and in Germany pumice from the Eifel volcanism is exploited.
Pumice from Lake Chiemsee
Since a few years the intensified geological investigations of the crater strewn field of the Chiemgau meteorite impact has revealed abundant finds of pumice cobbles in the shore region of Lake Chiemsee.
Fig. 1. Pumice varieties from Lake Chiemsee. White pumice – gray, marginally whitish pumice – gray pumice – grayish-black pumice (from top left to lower right). Samples by courtesy of Ernst Neugebauer.
The pumice occurs in various color varieties (Fig. 1) the white pumice rather being rare. Under the microscope the texture of the white form differs from the gray and grayish-black varieties (Figs. 2, 3). Continue reading “Chiemgau impact: Pumice as an impact rock (impactite)”
Presentation: 43. Lunar and Planetary Science Conference (LPSC), March 19–23, 2012, The Woodlands, Texas, USA: http://www.lpi.usra.edu/meetings/lpsc2012/programAbstracts/view/
Shumilova T. G.1 Isaenko S. I.1 Makeev B. A.1 Ernstson K.2 Neumair A.3 Rappenglück M. A.3: Enigmatic Poorly Structured Carbon Substances from the Alpine Foreland, Southeast Germany: Evidence of a Cosmic Relation [Abstract #1430]
1Institute of Geology, Komi SC, Russian Academy of Sciences, Pervomayskaya st. 54, Syktyvkar, 167982 Russia, 2Faculty of Philosophy I, University of Würzburg, D-97074 Würzburg, Germany, 3Institute for Interdisciplinary Studies, D-82205 Gilching, Germany.
The study deals with a so far unknown impactite from the Chiemgau meteorite crater strewn field incorporating a high pressure/high temperature carbon allotrop.
At the AGU (American Geophysical Union) Fall Meeting, December 5-9, two contributions focusing on special features of the Chiemgau meteorite impact strewn field have been presented:
Neumair, A. & Ernstson, K. (2011), Geomagnetic and morphological signature of small crateriform structures in the Alpine Foreland, Southeast Germany, Abstract GP11A-1023 presented at 2011 Fall Meeting, AGU, San Francisco, Calif., 5-9 Dec.
The poster may be clicked here: Poster Neumair & Ernstson
Ernstson, K. & Neumair, A. (2011), Geoelectric Complex Resistivity Measurements of Soil Liquefaction Features in Quaternary Sediments of the Alpine Foreland, Germany, Abstract NS23A-1555 presented at 2011 Fall Meeting, AGU, San Francisco, Calif., 5-9 Dec.
The poster may be clicked here: Poster Ernstson & Neumair
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
Continue reading “Chiemgau impact: an article on the impact-induced soil liquefaction (rock liquefaction)”
The term spallation is used in various meanings, e.g. in nuclear physics and fracture mechanics. For impact processes, spallation plays an important role (however seldom appreciated appropriately) and is closely related with the propagation of shock waves. To put it simply, the process runs as follows: On impinging on a free surface, the shock compressive wave is reflected as a tensile wave of practically identical energy. And while a compressive pulse is squeezing a rock, a tensile pulse is stretching the material thus enabling the development of tensile fractures and in an extreme case leading to the detachment of a spall or series of spalls. This is favored by the fact that the tensile strength of all materials and, hence, also of rocks is considerably less than the compressive strength. This is why it is often disregarded that the enormous destructions upon meteorite impact are not so much the result of the shock wave pressure as of the pull of the rarefaction waves. Spallation may take place also when a compressive shock pulse impinges on a boundary of material with reduced impedance (= the product of density and sound velocity) where part of its energy is reflected as a rarefaction pulse that may likewise enable tensile fracturing. It is worth remarking, however compatible with shock physics, that the process of spallation can be observed on arbitrary scales, from microscopically small deformations right up to the movement of huge rock complexes.
Fig. 1. A limestone cobble (14 cm long) exhibiting the typical open spallation tensile fractures. The process is nicely documented by the observation that the running fractures have come to standstill midway through the cobble. In case they had continued running, the cobble would have been fractionized to pieces, and nothing of note would have remained. Continue reading “Shock spallation – a typical impact process in the Chiemgau meteorite crater strewn field”
We are watching with interest discussions on relevant Wikipedia articles, and we would like to put the reader of this website in a position to receive a first-hand impression of the varied quality of the contributions to the discussion and to form her/his own opinion about the various versions of the Wikipedia articles:
The air photo (1)* originates from the northern part of the impact strewn field near Perach and shows (arrow) a crater leveled on an acre.
Image 1: Chiemgau impact; leveled crater near Perach
By image processing, the in the original photo only adumbrated structure gains amazingly sharp contours (2) clearly exhibiting four different concentric zones (3):
- a 5 m-diameter central area (black)
- a 12 m-diameter adjoining zone (red)
- an annular Zone not quite 10 m wide and with an outer diameter of c. 30 m (yellow)
- an exterior zone (60 – 70 m diameter) displaying extensions radiating up to 50 m from the center.
The following attribution of the individual zones is suggested:
The interpretation of the central spot orients by the GPR (ground penetrating radar) measurements (Dr. Patzelt, Terrana Geophysik; inhttp://www.rssd.esa.int/SYS/docs/ll_transfers/295499_Roesler_pres.pdf and http://www.rssd.esa.int/SYS/docs/ll_transfers/295499_roesler.pdf) that have been conducted over another crater (our crater no. 004 – also see http://www.chiemgau-impakt.de/mineral.html) located in the northern part of the strewn field. The GPR soundings show prominent reflections from the crater floor possibly related with strong compaction of the underground material. Assumed this compaction also exists within the Perach crater serving as impermeable rock, a corresponding moisture penetration could optically be traceable to the surface.
The adjoining 12 m-diameter zone could represent the material from the leveling of the crater. The annular zone is suggested to reflect remnants of the original rim wall. Taken the middle of this zone to have been the location of the rim crest, a 20 m diameter of the original crater results.
Finally, the exterior zone is suggested to reflect the zone of the crater ejecta radiating up to 50 m from the crater center.
This documentation of a ring structure illustrates that alternate explanations (geologic glacial formations, anthropogenic (archeological) structures, primitive industrial sites) readily and frequently given by opponents of the Chiemgau impact and skeptics of the meteorite origin for the innumerable craters, continue to have a hard time.
In any case, it is planned to investigate the Perach leveled crater by various geophysical measuring systems trying to characterize the optical zoning in more detail physically.
* In earlier texts, the air photo was erroneously labeled an infrared image.