A Catastrophe Remembered: A Meteorite Impact of the Fifth Century AD in the Abruzzo, Central Italy. (Research)

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The Sirente meteorite and its date

The Sirente crater is located at an altitude of 1100 metres in the Abruzzo Mountains, on a plain on the northern side of the 2348 metres high Sirente massif, inside the Sirente-Velino Regional Park (Figures 1 and 2). It shows strong geological similarities with known meteorite craters and was the first to be identified in Italy (Ormo et al. 2002 a & b). The Sirente crater consists of a main crater surrounded by a group of smaller craters distributed in a field covering about one square kilometre. The main crater is slightly oval with a well-developed rim 140 x 115 metres across rising about 2.2 metres above the surrounding plain. The morphology of the main crater and its relation to the crater field points to an impact from a projectile that broke up during the passage through the atmosphere. The main impact must have resulted in an explosion that vaporised the bulk of the meteorite (Ormo et al. 2002b).

[FIGURES 1-2 OMITTED]

The date of this event has been measured by radiocarbon. Bulk samples were taken from the upper 50 mm of the old ground surface defined beneath the crater rim, and extracted carbon measured with AMS. The date obtained was 1650 [+ or -] 40 radiocarbon years BP, which gives a calibrated age around 412 AD (Ormo et al. 2002a) (Figure 3). However, given the inevitably mixed sample, a date of the late fourth to early fifth century is probably the most precision that should be claimed.

[FIGURE 3 OMITTED]

Its effect

An idea of the likely consequences of such an impact can be obtained from modern eyewitness descriptions. The most famous is the Tunguska explosion that occurred over Siberia in 1908. It was an object that exploded at about seven kilometres height in the atmosphere and it did not leave any crater on the ground. However, about 2000 [km.sup.2] of coniferous forest were devastated by the blast, and about 100 [km.sup.2] were burnt from the heat of the explosion (Vasilyev 1998). Another famous meteorite fall happened in 1947 near Sikhote Alin in eastern Russia.

It is a crater-forming event that left over 122 small craters in a 1.6 [km.sup.2] elliptic field (Hodge 1994, and references therein). The largest crater is only 27 metres wide. The fall was seen by a large number of people. They described a fireball so bright that it hurt their eyes and outshone the sun. When the fireball had disappeared, loud explosions were heard, followed by a roaring noise. Doors were blown open, windows were broken, and plaster fell from ceilings. A huge dust train remained in the sky to mark the flight of the meteorite for several hours (Hodge 1994). An artist in a nearby town made a painting of the event, which later was used for a postage stamp of the USSR.

A more recent crater-forming event is the Sterlitamak impact, Bashkir Republic, in 1990. It landed in a soft sediment and caused a crater about 10 metres wide (Petaev 1992), too small to be a true explosion crater and fragments of the meteorite could be retrieved. Nevertheless, the appearance of the atmospheric entry is probably typical for larger meteorite falls. Petaev (1992) describes how numerous witnesses in the Bashkir territory observed a powerful fireball moving from south to north at an angle near 45 degrees to the horizontal plane and left behind zigzag-shaped light traces. The fireball was lit all the way until the moment of impact with the ground. The whole effect lasted for seven to eight seconds. Some seconds later several explosions were heard accompanied by ground shaking and glass rattling. A witness 1.6 kilometres from the crater noticed how the brightness of the fireball increased up to five stellar values, terminating with a bright flare and the appearance of a fireball with a tail, from whose motion was first extracted one fragment and 0.5 seconds later two more fragments.

It is estimated that the meteorite recorded at Kaali weighed about 450 tons on impact (Veski et al. …