The basic aim of this website is to contribute to a better understanding of the geologic process of impact cratering. Impact cratering comprises all aspects related with the formation of an impact structure including astronomical considerations, impacting cosmic bodies (impactors; meteorites, asteroids, comets), the various stages of the crater-forming process, geological and geophysical implications, impactites, shock metamorphism, impact experimental studies and scaling, and last but not least the social factor (NEO, Near Earth Objects, threat to mankind).

Image: NASA

The basic events during and after the meteorite impact process are largely understood since decades. More than thirty years ago, the late Eugene Merle Shoemaker, American geologist and astronomer, who pioneered the study of impact cratering on Earth, on the Moon, and on the other planets and their satellites, stated that impact cratering must be considered to have been one of the most important geological processes in the development of our planetary system. Some twenty years ago, the first textbook on “Impact Cratering. A Geologic Process” (Melosh 1989) was printed.

Nevertheless, the educational impact in schools and universities has been and is still poor. The majority of geologists still do not believe that extraterrestrial objects made a significant impact on the geology of planet earth. Partly bizarre ideas about the formation of impact craters are found among many geologists, and even the most common impact rocks like polymictic breccias, impact melt rocks, impact glasses, suevites and shattercones (spelled also shatter cones) have never been at their hands to say nothing of their knowledge of typical impact outcrops and of the simplest concepts of impact physics.

No wonder that even today the opposition of regional geologists can be considerable when an impact origin for a newly discovered structure is suggested.

This in mind, we began to construct the Ernstson & Claudin impact structures website in the late nineties, and we are now proud of posting a completely revised version. As before we focus on the geology of impact structures and impact processes and on impact rocks from various crystalline, sedimentary and mixed impact targets from all over the world. And like with the previous issue of the website, we attach great importance to graphical material like outcrop, impactite and micrograph images.

Azuara impact structure. Google Earth.

Apart from the Ries, Steinheim (Germany) and Rochechouart (France) impact structures which among the European sites are especially familiar to us, the main part of our homepage is dedicated to the large Spanish Azuara and Rubielos de la Cérida impact structures. This is done for the following reasons. We (the authors F.C. and K.E., and co-workers) have now been working for more than 25 years in this geologically exiting impact region. During this time we carried together a host of material in the form of innumerable outcrop studies and descriptions, many big cases of impact rocks as well as abundant petrographic evidence of impact. The impact region measuring 120 km in length at least, is distinguished by the excellent outcrop conditions, the great variability of geological impact scenarios and the easy access. While in the Yucatán region with the famous buried Chicxulub impact structure impact samples must be drilled from kilometer-deep boreholes at enormous costs, comparable samples can easily be taken with the hammer in the Azuara/Rubielos de la Cérida area (at the same time a wonderful landscape), and quite a few of the outcrops may be and have been termed geologically educational.

There is one more reason to consider the Spanish impact structures and their investigations educational. The Azuara – Rubielos de la Cérida impact represents the typical case of a controversy concerning its origin. Those hard-fought controversies are well known for the Vredefort, Sudbury, Ries and many other impact structures. All controversies proceeded nearly identical bringing the regional geologists to the scene. For them, the impact of a cosmic body was incompatible with the regional geology. They thus ignored that meteorite impact is a completely statistical process and that an impacting body will not take care of the regional geology (and the regional geologists).

For the Azuara – Rubielos de la Cérida impact structures the same debates have been conducted, backed by a part of the so-called “impact community” (whatever that may be), and that is why we dedicate a special and comprehensive chapter to this Azuara – Rubielos de la Cérida controversy shedding some light on how science is (mal)functioning.