Since a few years there is evidence of a dual meteorite crater at the bottom of Lake Chiemsee (Fig. 4) in the Chiemgau meteorite crater strewn field. The search for a suspected impact into the lake was originally based on reports of fishermen about unusual sharp-edged large stones at the lake bottom that had damaged their fishnets. Such stones are in fact foreign matter in the lake. A general echo sounder campaign, followed by a detailed survey veritably revealed a peculiar structure, likewise a foreign element in the lake, with all evidence of a rimmed doublet crater (Fig.1).

Fig. 1. The proposed meteorite doublet crater at the bottom of Lake Chiemsee from detailed sonar echo sounder measurements. Meter scale indicates water depth.

The similarity to meteoritic dual craters on Mars is striking (Fig. 2). From the Mars image it is evident that the doublet structure formed on synchronous impact of twin projectiles. Continue reading “Chiemgau impact: the dual crater at the bottom of Lake Chiemsee – nice counterparts”

  Continue reading “Chiemgau impact: Shock metamorphism (diaplectic glass) in the #001 crater, the Carancas (Peru) crater, and the question of the formation of very small hypervelocity impact craters.”

Experimental hypervelocity impact crater generation and the formation of the Lake Tüttensee crater

Fig. 1. Snapshot of a hypervelocity impact into flour taken from a high-speed camera video. The full video may be played back by clicking on the image.

Meteorite impact is a fascinating geologic process that for many geologists, however, has remained enigmatic. Therefore we are glad to present here on our website some results of experimental impacts that have been recorded by high speed cameras. This has been possible by a cooperation between the CIRT and Werner Mehl who is a world-wide known specialist for ballistics and high speed photography http://www.kurzzeit.com/eng/startseite.htm).

Fig. 2. Experimental hypervelocity 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 on the image in Fig. 1 the full video can be  played back 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: Continue reading “Chiemgau impact: conducting hypervelocity impact experiments”

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)”