Fig. 1. Experimental impact crater produced by a projectile (as lying in the hand) in a target of flour. The angle of the impact trajectory was 30°. On CLICKING a video can be downloaded that shows the impact process recorded with a high speed camera. The outer ring-like fold of the foil is a side effect of the experimental set-up.

Details of the experiment are as follows:The projectile (the “meteorite”) is a 5 mm-diameter plastic sphere (Fig. 1). It is shot by a gun (Fig. 2) and leaves the barrel at a velocity of c. 1,500 m/s. On impact the velocity is lowered to still c. 1,250 m/s. This is a remarkably high velocity with regard to the comparatively low efforts W. Mehl makes with these unusually instructive experiments. Impact experiments performed by other institutions are utilizing “canons” of entirely different dimension.

Fig. 2. The gun positioned for a very flat angle of incidence. To the right on the floor the “impact target”. 

The velocity of the accelerated projectiles is a basic factor for these experiments of crater formation. As has repeatedly been mentioned here on our website true impact craters are formed by hypervelocity projectiles, i.e. the projectiles must impact at a velocity exceeding the sound (seismic) velocity in the target. Then, shock waves are generated which are indispensable for the formation of meteorite craters. On impact of cosmic projectiles arriving at cosmic velocities (in the range of c. 10 – 70 km/s) these conditions are fulfilled, of which more HERE.

It goes without saying that the experiment must also meet this requirement, and this is why the projectile velocity produced by the gun is so much important as is the choice of the target material. In this special case, flour has been chosen which is estimated to have a sound velocity of the order of 100 m/s. Hence, the impact velocity of the plastic sphere of mentioned 1,250 m/s is considerably larger. Consequently shock waves are propagating into the flour target, and observers not being in the “secret” are most surprised seeing that this tiny projectile is able to produce such a big crater (Fig. 1). That’s impact physics!

The video to be downloaded here was taped with a high speed camera. The cameras used by W. Mehl are able to record up to 1 Mill. images/second, and 3D mode with a pair of cameras is also routine. In the impact experiment reports to follow we will publish respective 3D movies showing impressive processes of crater development.

The video file shown here had an original size of 1 gigabyte and for good reasons had to be cut low for this presentation. On regarding the video (preferably in multiple re-run) the most important sequences of the crater formation including excavation and the developing ejecta curtain can be studied. They are producing the rim wall merging into the ejecta blanket of decreasing thickness around the crater.

Something like this, the formation of the Lake Tüttensee crater in the Chiemgau impact event has to be imagined, and we suggest that the doubters of the impact origin still perpetuating the dead-ice theory should view the movie on every occasion. After that they possibly will understand how the rim wall around Lake Tüttensee was formed, and perhaps they will realize the formation of the impact catastrophic ejecta layer that has been uncovered by innumerable geologic excavations near the Mühlbach creek, in the town of Grabenstätt (Stefanutti excavation), and elsewhere.

Very instructively, the video shows how already during the expansion of the ejecta curtain considerable bulks of the just developing rim wall are flowing back into the still enlarging crater. Exactly this has to be envisioned with the Lake Tüttensee: As early as during and shortly after the crater formation bulks of the uncemented gravelly sediments of the ring wall are moving into the cavity partly backfilling it. This can be seen also from seismic sediment echo sounder measurements on Lake Tüttensee. There are no finely bedded sediments beneath the lake bottom as is well known from other pre-alpine lakes; instead the seismograms reveal a wealth of diffraction hyperbolas as the result of seismic diffraction effects with the debris of the replenishment. Ignoring this special crater formation process, geologists of the Bavarian geological regional authorities (LfU), all but familiar with impact cratering, have drilled a borehole for sediment dating purposes erroneously interpreting their data in terms of the Lake Tüttensee age.

A very interesting observation can be made at the very beginning of the movie directly shortly after the contact of the projectile: Ejected target particles are leaving the ground with the beginning crater development at extremely high velocities (which have been estimated to be as high as several 1,000 m/s) (recommendation of starting the film several times in quick succession). Impact physics gives an explanation and points to a superposition of shock and rarefaction waves in the so-called interference zone leading to the high-velocity ejection of the so-called spall plates. As for the Chiemgau impact and the Lake Tüttensee meteorite crater this process is very remarkable in so far as “erratic” large blocks were again and again excavated from near-surface purely loamy ground (in part at larger distance from Lake Tüttensee) having regularly puzzled the locals. Now, this may be understood with regard to such spallation “missiles”.

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).

Fig. 2. Differing texture of the white and grayish/blackish varieties.

Fig. 3. White and grayish/blackish pumice varieties from Fig. 2 in close-up.

The difference becomes especially evident on larger magnification (Fig. 3) which shows distinctly broader partitions between the bubbles for the white pumice, for their part also exhibiting vesicular texture.

The difference is also a matter of material: An acid test of the white pumice shows a high carbonate amount which is very low in the grayish-black pumice. This  corresponds with differing consistency. While the white pumice can easily be crumbled with one’s fingers the grayish-black pumice reacts with finest pulverization. In both cases the compressive strength is low as shown by simple indenting with the fingernail.

 Grains under the microscope

Fig. 4. Grinded pumice on grain slide under the polarization microscope. Upper: grayish-black pumice (plane polarized light). – Lower: white pumice (crossed polarizers). In the lower middle of the image a quartz grain can be observed that exhibits planar fractures (PFs). The images are c. 500 µm wide.

Grain slides under the microscope are underlining the difference. The ground material of the grayish-black pumice (Fig. 4, upper) shows finely fractured shards of glass (extinction under crossed polarizers). Few mineral grains (quartz, white mica) and minute carbonate aggregates are interspersed. The glass itself shows vesicular texture and opaque lining of the voids.

The grains of the white pumice (Fig. 4, lower) consist of aggregates of finest crystallites which according to the acid treating should be carbonate (calcite). Compared with the glass in Fig. 4, upper, considerably more quartz grains, mostly sharp-edged fractured and sized of the order of 20 µm, are interspersed.

Fig. 5. Quartz grain exhibiting planar fractures (PFs) along three different orientations. The image is c. 30 µm wide.

Within the quartz grains the occurrence of planar fractures (cleavage) (Figs. 4, 5) is a prominent attribute. In the white pumice a large part of the numerous quartz grains show these fractures.

Origin

Volcanism?

Although pumice is a typical volcanic rock, an on-site volcanic formation can basically be excluded. An “import” of the pumice from known volcanic areas is in principle imaginable (for example in connection with Roman settlement). Because of the predominantly carbonate white pumice this explanation presents a nearly insoluble problem. Moreover, it doesn’t make much sense if pumice “imported” from some dark side and for unknown purposes was thrown into Lake Chiemsee in larger quantities to strand, nicely rounded, some decades later on the shore.

Anthropogenic, technical product?

Artificial products that are adapted from pumice are known in manifold variants. This includes, e.g., cellular glass, expanded glass, expanded clay, and foamed or porous concrete. As for the internal structure these materials are similar to the pumice as described. For a possible confusion, expanded glass and expanded clay are out of the question because they are produced in small granulation and in nodular form, respectively. Porous concrete consists mainly of a crystalline phase and not of glass and, moreover, is free of carbonate. In addition, all these technical products share a high compressive strength and acid resistance, and exactly these properties are lacking in the case of the Lake Chiemsee pumice. And like with the hypothetical volcanic origin these technically produced materials must ages ago have been thrown into Lake Chiemsee in considerable quantities so that they are today can be sampled as well-rounded cobbles.

The Lake Chiemsee pumice as an impact rock (impactite)

Like with the explosive volcanism, the meteorite impact process offers virtually ideal conditions for the production of pumice if certain requirements are fulfilled. For a better understanding it is once more pointed to the basic importance of shock wave propagation in an impact event. Behind the shock wave front of extreme pressure, extreme temperatures emerge on pressure release which, following the zone of vaporization, lead to melting of the impacted underground (see, e.g. here: http://www.impact-structures.com/understanding-the-impact-cratering-process-a-simple-approach/).

If the rocks in the ground are containing much water a mixing of the impact “magma” with the shocked water may occur, and on shock pressure release the same happens exactly like with the explosive volcanism: frothing of the rock melt and, on rapid cooling, the formation of a highly porous glass, the impact pumice. If in addition carbonate rocks (e.g., limestone) are contributing the shock-produced carbon dioxide may boost the process, and different from normal volcanism carbonate melt may be formed.

Exactly these conditions appear to have perfectly been fulfilled in the case of the Chiemgau impact. From the detailed SONAR echosounder measurements individual projectiles of the large impactor have evidently crashed into Lake Chiemsee as is documented by the rimmed doublet crater at the bottom of the lake. And there the already mentioned ideal conditions were met: a water-saturated sediment composed of glacial deposits, lake calcareous mud and clay.

Melting und explosive degassing of the silicate clay led to the formation of the grayish-black pumice, and carbonate rocks and lake calcareous mud were the source material for a carbonate melt being converted to the white, predominantly carbonate pumice.

This interpretation is supported by the occurrence of the already mentioned abundant quartz grains in the pumice matter exhibiting planar fractures (PFs, Figs. 4, 5). Although not proving in the strict sense PFs are strong evidence for a shock damage.

More detailed investigations of this peculiar pumice material will follow.

Affinities of pumice and the Chiemgau impact melt rocks (“swimstones”) as well as similar formations (volcanic and impact scoria) will also be discussed soon.

A foamy pumice texture in glasses from the Bosumtwi impact structure in Ghana has been reported by  Boamah, D. & Koeberl, C. (2006): Petrographic studies of “fallout” suevite from outside the Bosumtwi impact structure, Ghana. – Meteoritics & Planetary Science 41, Nr 11, 1761–1774.

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.

Abstract download:

http://www.lpi.usra.edu/meetings/lpsc2012/pdf/1430.pdf

Poster download:

Poster LPSC

The study deals with a so far unknown impactite from the Chiemgau meteorite crater strewn field incorporating a high pressure/high temperature carbon allotrop.

So far, shatter cones have never been found in the crater strewn field of the Chiemgau impact as a positive impact evidence, which we explained by the predominant uncemented loose sediments of the impact target. In this regard, a change of thinking is necessary since only recently clear shatter cone structures were detected in a rock sample from the Lake Tüttensee ring wall (Fig. 1).

Fig. 1. Shatter cones with counter orientation from the Lake Tüttensee crater.We are seeing a double cone of counter orientation weathered from a fine-grained sandstone along the fracture surfaces where the frustrums are preserved (Fig. 2).

Fig. 2. The graphically completed frustrums of the counter shatter cones. – The circular conic section of the larger cone.

A shatter cone from the Crooked Creek meteorite crater in Missouri, USA, allows a fine comparison (Fig. 3).

Fig. 3. The Lake Tüttensee shatter cones in comparison with a shatter cone in dolomite from the Crooked Creek meteorite crater, Missouri, USA. 

Although weathered, the typical horsetail fracture markings of the Lake Tüttensee shatter cones can still be recognized. A confusion with other structures (cone-in-cone structures, lancet fracture markings, ventifacts, etc.) often seen with inexperienced observers and mistakenly shown even in the internet, can be excluded.

Because of the find in the area of the impact ejecta of the Lake Tüttensee ring wall we have to assume that the shatter cones formed near the central impact point where the necessary shock pressures (roughly 2 – 20 GPa) were obtained, before they were excavated and ejected as rock fragment. We are unable to reconstruct the shape of the original rock. Possibly it was a big moraine erratic block or a larger sandstone component as part of a thick Nagelfluh (= strongly cemented conglomerate) plate. Large sharp-edged rock fragments are still today found on the Lake Tüttensee bank. It is unknown, however not to be excluded entirely, whether shatter cones can form also in individual cobbles. There is still much open with regard to the process of shatter cone formation. For example, till this day it is unresolved why in the mixed target of the Ries impact structure clear shatter cones are only known from crystalline rocks but have never been found in optimally suited Malmian limestones although pressure conditions must have been fully adequate.

As for the Ries crater shatter cones we note that they are not only found in crystalline rocks exposed within the crater (e.g., in the abandoned Wengenhausen quarry) but can be sampled also as nice specimens from the Bunte breccia ejecta. These are the same conditions as obviously fulfilled at Lake Tüttensee: The shatter cones develop in the very beginning of the cratering process on passage of the shock wave and are then ejected with the shocked rock.

The combination of counter cones with the Lake Tüttensee shatter cones is remarkable. In general and statistically verified, the cone apices more or less point towards the source of the shock deformation. However, strongly varying orientations are observed, and frequently – as in the Lake Tüttensee case – reverse cones occur. This can be explained physically (David 1977) not further considered here. In the case of the Crooked Creek shatter cones (Fig. 3) reverse cones are relatively abundant, and in Fig. 4 and Fig. 5 examples from the Steinheim and Kentland impact craters are shown.

Fig. 4. Reverse shatter cones as negative and positive in Malmian limestone. Steinheim Basin impact structure, Germany.

Fig. 5. Two shatter cones exhibiting counter orientation. Kentland impact structure (Indiana, USA).

Summarizing we conclude: The original opinion that the dominating loose sediments of the Chiemgau impact target have prevented shatter cone formation can obviously no longer be maintained. Therefore, it may be promising to look for more respective pieces of evidence, which requires memorization of the most important features of these very peculiar fracture markings. The probably most comprehensive information about shatter cones may be clicked here:

http://www.impact-structures.com/impact-rocks-impactites/the-shatter-cone-page/

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

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. For a better understanding we add that fractures always begin at a definite point within the material propagating from there with a certain fracture velocity which may change during propagation and may even become zero. Then the fracture stops unless it is again fed with energy and continues running.

As for the Chiemgau impact and shock spallation quite peculiar conditions are met namely particularly in the form of very solid cobbles of Alpine lithology. Apart from the occurrence as components of the strongly cemented Nagelfluh plates, the cobbles are in general found in loose bulk and, hence, predestined for a reaction to the passage of shock waves with resulting spallation. It’s not just the extreme contrast of impedance at the cobbles’ surface, also their frequently nodular shape may boost the effect by internal focusing of the shock and rarefaction waves in part yielding enormous energy densities.

As early as in the beginning of our impact research in the Chiemgau crater strewn field we have reported on these deformations and have shown typical photos of spallation fractures down to microscopic scales. Here, we present new examples from recent investigations near the small town of Obing north of Lake Chiemsee. The reader may forgive our keeping secret about the precise coordinates of the impact sites. Our bad experiences with ransacked smaller craters and with the Tüttensee crater where practically all rocks with impact-typical deformations have been removed by rock hunters or people disliking our impact research are forcing us in order to preserve these peculiar impact features for science and interested scientists.

Fig. 2. A quartzite cobble exhibiting a prominent spallation fracture which like the rock in Fig. 1 has not completely split the cobble. In Fig. 3 we point to features very characteristic of spallation fracturing.

Fig. 3. A close-up of the spallation fracture in Fig. 2 shows some typical behavior: Frequently, the pathway of the spallation fracture proves to be a mirror image of the cobble’s surface curvature, and in the case under discussion we have marked the axis of mirror symmetry by a blue dashed line. This may be understood as a consequence of the reflection of the shock (compressive) wave at the free surface for geometrical reasons leading to a mirrored front of the reflected rarefaction wave.

Fig. 4. Spallation fractures in a gneiss cobble. Here again the open fractures do not split the cobble completely, and here again the geometry of the roughly perpendicularly oriented ruptures mirrors the shape of the angular cobble.

Fig. 5. Open spallation fractures in a garnet amphibolite.

The examples of spallation fractures in quartzite, limestone, gneiss and amphibolite cobbles demonstrate that the process is independent of rock lithology und produces recurrent features.

To obviate objections these deformations have already originated from tectonics in the Alps (regularly claimed by local geologists) and have been transported in the form of cobbles in rapid glacial and post-glacial streams and in the end to have been deposited near Obing north of Lake Chiemsee, we point to the frequently very fragile character of the cobbles. Moreover, any strong pressure having acted on the cobbles can basically be excluded because they would inevitably have been broken and sheared.

For comparison spallation like in cobbles from the Chiemgau crater strewn field is shown in the next figures with examples from the Ries impact crater und the Spanish Azuara http://pubs.giss.nasa.gov/abs/er01000b.html Rubielos de la Cérida impact structures. The latter occurrences have been investigated more intensively including spallation experiments. A related article has been published in the prestigious GEOLOGY journal (see here where the full article can be downloaded), and an extended report may be read here.

Fig. 6. Limestone cobble from the ejecta (Bunte Breccia) of the Ries impact structure (Nördlinger Ries crater) showing spallation fractures that have not split the cobble. After the shock spallation the deformation of the cobble continued – probably in the course of excavation – without dissecting it.

 Fig. 7. Quartzite cobbles from the Spanish large Azuara and Rubielos de la Cérida impact structures showing very typical shock-induced open spallation fractures. For some of the fissures the rough mirror symmetry of surface and fracture geometry becomes again evident. 

http://en.wikipedia.org/wiki/Talk:Chiemgau_impact_hypothesis

THE CHIEMGAU METEORITE IMPACT AND TSUNAMI EVENT (SOUTHEAST GERMANY): FIRST OSL DATING

I. Liritzis, N. Zacharias, G.S. Polymeris, G. Kitis, K. Ernstson, D. Sudhaus, A. Neumair, W. Mayer, M.A. Rappenglück, B. Rappenglück

Mediterranean Archaeology and Archaeometry, Vol. 10, No. 4, pp. 17‐33

The full article may be clicked here:

PDF

[1] A POSSIBLE NEW IMPACT SITE NEAR NALBACH (SAARLAND, GERMANY)
E. Buchner, W. Müller and M. Schmieder
www.lpi.usra.edu/meetings/metsoc2011/pdf/5048.pdf
[2] NALBACH (SAARLAND, GERMANY) AND WABAR (SAUDI ARABIA) GLASS – TWO OF A KIND?
M. Schmieder, W. Müller and E. Buchner
www.lpi.usra.edu/meetings/metsoc2011/pdf/5059.pdf
[3] IMPACTITES AND RELATED LITHOLOGIES IN GERMANY – CURRENT STATE OF KNOWLEDGE
M. Schmieder, W. Müller, L. Förster and E. Buchner
www.lpi.usra.edu/meetings/metsoc2011/pdf/5060.pdf

Among the authors W(erner) Müller is particularly singled out who has only recently performed meticulous field work near the town of Nalbach in the Saarland region near the French border. He sampled a large amount of peculiar rocks and natural glasses as well as suspected iron meteorites. From these finds he concludes the possible existence of a meteorite impact only in younger times, and as the discoverer of the phenomenon he has published an article in the Scribd scientific internet forum:

Prims: a possible Holocene meteorite impact in the Saarland region, West Germany
which may be clicked HERE

This postulated meteorite impact is shortly attended by the other authors in the above-mentioned abstracts where the original Scribd article is referred to only in abstract [2], but strangely not in abstract [1] obviously standing more to reason thematically.

The close relation to the Chiemgau impact arises from Werner Müller’s Scribd article and, hence, comprises the abstract articles of Buchner et al. and Schmieder et al. As can be read in the article of Müller and especially pointed out by him, many striking parallels to finds in the Chiemgau meteorite crater strewn field are obvious:
– pebbles and cobbles showing mechanical load and high-temperature signature in the form of glass coating and interspersing the in most cases sandstone samples
– polymictic breccias
– slag-like melt rocks
– glass as matrix of melt rocks with various rock fragments
– glass-like carbon
– spherules
– probably shock-induced spallation effects in melt rocks

The reader is encouraged to take a look at the images in Werner Müller’s Scribd article and to compare them with the Chiemgau samples. Images are to be found on the website http://www.chiemgau-impact.com/petrographie.html and in the Ernstson et al., 2010 article or, as originals, in the Grabenstätt impact museum

Although there is so far no definite age for the postulated Saarland impact, W. Müller, because of first-sight field impressions and considering the in most cases very fresh glasses, clearly favors a Holocene age. Hence, with regard to the Chiemgau impact Holocene age the obvious question arises whether the Chiemgau and Saarland impacts may belong to the very same cosmic event. This can be imagined given the cosmic projectile was already in disintegration when approaching Earth (like, e.g. in the 1994 Shoemaker-Levi-9 comet crash with Jupiter) and in the end leaving impact scars in an even much larger strewn field than hitherto assumed for the Chiemgau impact.

From this viewpoint of a relation of both phenomena it is rather remarkable if the CIRT research project on the Chiemgau meteorite impact achieves considerable support by two of the abstract authors (E. Buchner, M. Schmieder) as is well known confirmed opponents of the CIRT research and of the Chiemgau impact at all. Notably the hint of Buchner et al. [1] to a possible meteoritic airburst to have produced the Saarland impact signature raises attention because such a possibility has already been discussed for the Chiemgau impact event in the context of the formation of some peculiar craters there (e.g. Ernstson et al., 2010, S. 92-93).

A comment on the abstract article of Schmieder et al. [3] is being added. The authors refer to several structures in Germany for which a meteoritic origin has been postulated, “[cit.] however, all of these geologic features currently lack evidence for shock metamorphism and/or meteoritic matter as proof for impact”. Among these structures, the Chiemgau impact has been classified, thereby referring to the 30 pages article ‘Ernstson K. et al. 2010. J. Siberian Fed. Univ. Engin. Technol. 1:72–103 (HERE to be downloaded)‘ Either have Schmieder and Buchner never read this basic and comprehensive article about the Chiemgau impact or they calculatedly conceal that on p. 82-83 under the heading 8. Shock metamorphism generally accepted impact shock effects in rocks from the Chiemgau craters together with several photomicrographs are reported. The shock effects include multiple sets of planar deformation features (PDFs) with up to five sets in one quartz grain, and diaplectic glass requiring even higher shock pressures of formation than do PDFs.

This keeping silence about proofs for the Chiemgau impact and at the same time claiming the Chiemgau impact is not confirmed [3], is rather odd with regard to the fact that comparably unambiguous impact proofs for the Saarland phenomenon could so far not be presented [1].

Owing to the promising similarities between Chiemgau impact material and material from the Saarland area we can but encourage the colleagues to perform continuing research. We are glad to see that the research of Buchner and Schmieder on the Saarland impact contributes to a better understanding of the Chiemgau impact, even though their work features some deficits and oddness.