Sirente crater
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The Sirente crater (Italian: Cratere del Sirente) is a small shallow seasonal lake in Abruzzo, central Italy. The depression, which is located at the center of the Prati del Sirente, a mountainous highland north of the Sirente massif in the Apennines, is 13 km (8.1 mi) from the village of Secinaro. Its formation has prompted a number of theories in recent years, including a meteorite impact.
Interest in the Sirente crater began in the late 1990s after Swedish geologist Jens Ormö, an impact crater specialist, noticed ridges near the site that indicated a bolide collision. A research team named "The Sirente Crater Group" along with two scientists from the International Research School of Planetary Science of Pescara (IRSPS) began a detailed examination of the area. The team concluded the meteorite struck the Earth with the force of a small nuclear bomb; approximately one kiloton in yield. The blast would have created a mushroom cloud and shockwaves similar to a nuclear explosion.[1]
Meteorite
The Sirente Crater Group proposed a meteoric origin for this structure in the late 1990s and results were updated in the following decade.[2][3] A calibrated age of 412 AD was given in 2002.[4]
Anthropogenic (humans)
In 2004 a group of geologists led by Fabio Speranza working in the Istituto Nazionale di Geofisica e Vulcanologia hypothesized that the lake basin was excavated by humans in order to collect natural water for livestock.[5] A similar "shepherdogenic" hypothesis was that the site was a sheep dip, considering the lack of any evidence for impact shock in the area.[6] The nature of the depressions are now believed by Speranza et al. to be karstic or be the result of human activity combined with the action of natural karstic processes.[7] Although the crater lake was suggested to be just part of a larger crater field comprising about 30 individual depressions in the Sirente area, studies have shown the “crater field” is more likely to be the result of human activity.[7]
The theory of the combined anthropic excavation and karstic origin for the Sirente crater doesn't seem however compatible with the result of some seismic and electrical resistivity tests that were performed under the surface of the Sirente lake. More specifically, the geological structure appears too deep to have been excavated by humans in a highly unstable material context and a downward continuation typical of the underground removal of material during karst development is also lacking.[8]
Large numbers of metallic fragments have been found in samples taken from within the crater area. Analysis has proved they were pieces from exploded ordnance such as bombs and grenades. This had led to the theory that wartime bombing could also be the cause of the crater.[9]
Geological
In 2005 Dr Francesco Stoppa from the Gabriele d'Annunzio University proposed that a rapid emission of mud and/or water could also be a potential cause for the basin's formation.[10]
