|Issue number 25 : 20/05/2004
A scientific publication by SGF and NEODyS
An anthropogenic origin for the Sirente crater
by Fabio Speranza - Istituto Nazionale di Geofisica e Vulcanologia
In our paper ["An anthropogenic origin of the 'Sirente crater', Abruzzi, Italy", by F. Speranza, L. Sagnotti and P. Rochette, Meteoritics & Planetary Science 39, Nr 4, 635-649 (2004)] we report the results and the conclusion of a specific study on the morphological and geological characters of the Sirente plain, on the comparative analysis of several lakes from neighbour Abruzzi highlands which are very similar to the Sirente lake, and on geophysical and geochemical analyses carried out on soils and paleosols from Sirente and other Abruzzi localities.
We conclude that the lake from the Sirente plain is not the result of a meteoritic impact, but rather is the well preserved relict of an efficient hydraulic work created by man, taking advantage of a natural setting favourable to the accumulation and retain of water. Besides the fact that in the Sirente plain none has ever found any meteorite fragment, nor shocked or fused materials, nor high-pressure minerals, nor microspherules, nor a significant abundance of typical ET elements (such as Ir), the conclusion of our work is founded on four additional lines of evidence:
|From the left to the right: Lago di Filetto (diameter 91 m); Lago di Barisciano (diameter 124 m); an unnamed sag pond in the locality “Il Prato” (diameter 49 m); an unnamed sag pond in the locality “Le Locce” (diameter 51 m) (Photographs: copyright Speranza et. al, images taken from the article).|
|A map showing the location of the Gran Sasso sags and Sirente plain and the principal paths (dashed-lines) of the seasonal migration of herds from Abruzzi to Apulia (from Regione Abruzzo 2000 - image taken from the article).|
Moreover, the "crater field" (according to Ormo et al., 2002) around the Sirente lake is in fact simply composed by dolines, which are common in karstic environments and widespread over Sirente and the other Abruzzi carbonate massifs. These dolines are filled by soils (as they normally do), none has a raised rim, and the radiocarbon ages reported by Ormo and colleagues for the formation of the main lake and of one of the smaller dolines differ (significantly) by more than two millennia, thus excluding that they were all contemporaneously formed by a meteoritic impact.
As a conclusion, all the available observations and data suggest that the Sirente lake, together with analogous large sags in the Abruzzi intermountain plains, have to be attributed to the historical phenomenon of "transumanza". Such sags were excavated and used for several centuries, at least, to provide water for millions of sheep, which spent summers in the Abruzzi karstic high pasture lands, on carbonatic massifs deprived of natural superficial fresh water. The present aspect of such sags is due to a combination of natural features and human activities spread over a significant time. We have no definitive element to constrain the period of the main phase of excavation for all these sags, since the transumanza custom is documented in Abruzzi since Bronze age (ca. 2000 BC), has prospered in the Roman period, and reached its acme in late Middle Age-Renaissance times. However, relying over several bits of evidence, we speculate that the present aspect and the distribution of such water reservoirs in Abruzzi mostly reflect the pastoral activity of such last period (i.e. during the XII-XVII centuries AD).