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The Sirente Crater Field

The first impact structures in Italy

Impact crater geology has been integrated as an important part of the planetary research conducted at IRSPS. Studies of craters in images from Mars, Venus and other bodies in the Solar System are combined with fieldwork on terrestrial craters. Projects are currently carried out on craters in many different parts of the world (e.g. Mongolia, Africa).

The first impact craters in Italy have been recently discovered in the Abruzzo mountain range. They form a crater field of more than 20 structures and they are extremely well preserved, having a very young age (about 1500 years).

The Sirente crater field is in the Sirente-Velino Regional Park, in the Abruzzo inland. It is located in a small mountain plain, called Prati del Sirente, just North of the Sirente massif (2348 m)

ASTER Satellite image (RGB-321) covering the Prati del Sirente plain: The main crater, occupied by a small seasonal lake is clearly visible. In this combination of bands the vegetation appears from red to greenish. (Click to see larger version)

The Sirente Crater Field has been discovered by Jens Ormo in late '90 during his post-doctoral period at IRSPS. A research group was immediately formed, together with Angelo Pio Rossi and Goro Komatsu The main structure, currently occupied by a small seasonal lake, first attracted the attention of the research group, which started working about 2 years ago. A profile of the discoverers is available in this page.

Map of the crater field: the crater field is located in the Western end of Prati del Sirente plain. The small craters in the field are concentrated only in its westernmost portion. The distribution of craters in the field suggests that the projectile had come from western quadrants (from Ormo et al., 2002). (Click to see larger version)

The crater field consists of a larger structure, currently filled by a temporary lake, and several smaller craters, scattered in the western portion of Prati del SIrente plain.

Various studies have been carried out on the Sirente crater field in a few years following the initiation of the investigation, including detailed morphometric measurements, drillings, excavations and geophysical surveys. Further studies are currently ongoing.

3-D model of Sirente Main Crater: the structure has a prominent rim, with a maximum height of 2.2 meters and a width up to 10 meters. (courtesy of M. Marchetti, INGV) (Click to see larger version)

History of the discovery

During the first reconnaissance trip to the lake it was clear that the lake was larger than first expected and that it showed a striking resemblance to small impact craters known from other areas in the world. Due to the geological setting of the lake and its voluminous elevated rim it was soon clear that is origin was not compatible with karst.

After ruling out some other alternative causes of formation based on the local geology (e.g. volcanic), only three plausible alternatives remained: periglacial feature (i.e. Pingo), a man-made water reservoir, or an impact crater.

The morphology of the main crater was studied by detailed leveling of the elevated rim and close surroundings. This gave that the elevated rim rises about 2.2 m above the surrounding plain and that it is 15 m wide. It was also evident that the lake was slightly oval with a maximum rim-to-rim diameter of 140 meter. The studies continued with core drillings, one near the centre of the lake (7 meters in length) and two on the elevated rim (3 meters and 5 meters in length). The core drillings confirmed that the lake depression is developed entirely in soft sediments. Radiometric carbon dating of material in one of the cores from the rim gave that the elevated rim is formed by overturned material in a way typical for impact crater rims, and that the age of formation could be set to the 4th or early 5th century AD.

The partial excavation of two of the small craters in the field allowed to study their internal structure, also ruling out a karst origin for them as well.

The Sirente Research Group (from left to right: Ormo, Rossi and Komatsu) during fieldwork, drilling the northern rim of the main crater. The spectactular northern scarp of the Sirente massif is visible in the background. (Click to see larger version)

Theoretically, an impact crater of the size of the Sirente lake depression cannot exist alone. It must be surrounded by a field of small craters. This is due to the fact that small cosmic objects that approach the Earth would fragment during the passage through the atmosphere, producing a cluster of craters on the surface. In the case of sirente the biggest fragment should have produced the main structure, with a prominent rim. The spatial distribution of the craters in the field allow us to hypothesize a roughly NW direction for the incoming object.

Close-up of one of the small craters in the crater field (crater C1 in foreground). The diameter of these craters is ranging from few meters up to 15 meters. (Click to see larger version)

Usually the velocity of such objects (e.g. asteroids and comets) when they impact the Earth is about 20 km/second (but it can vary). It is more than 20 times the velocity of a bullet from a high-velocity rifle. The collision with the atmosphere generates so high stresses in the object that it breaks apart. Only objects forming craters larger than about 1 km in diameter can survive the passage through the atmosphere as reasonable coherent bodies.


3-D view of Sirente massif and surroundings. The Prati del Sirente plain is well visible, as well the small lake corresponding to the main structure in the crater field. (ASTER imagery draped on ASTER-derived digital elevation model, data processing by A. P. Rossi)

Viev a MPEG4 movie of Sirente massif in 3-D Link to .mp4 file, Link to .avi file


How to reach the crater

Location map of the Sirente crater field. The structures are easily accessible, just few hundreds of meters from the road (modified from Ormo et al., 2002). (Click to see larger version)

The Sirente Crater field is located in a protected area, in the Velino-Sirente Regional Park, inside the Secinaro municipality. If you plan to visit the structures please keep this in mind.

From Rome

Take the A24, continuing on A25 highway towards Pescara. Exit at AIELLI-CELANO. Continue on S.S. 5bis. Just before entering Rocca Di Mezzo turn on the right for SECINARO. The crater about 7 km far, on the right.

From Bologna

Take the A14 towards south. After PESCARA-NORD take the next exit for the A25 highway (Pescara-Roma). Exit at AIELLI-CELANO. Continue on S.S. 5bis. Just before entering Rocca Di Mezzo turn on the right for Secinaro. The crater about 7 km far, on the right. You can alternatively (beautiful landscape!) exit at PRATOLA PELIGNA-SULMONA, passing through RAIANO, CASTELVECCHIO SUBEQUO, SECINARO, ROCCA DI MEZZO (beautiful landscape!). The crater is after few km on the left.


Literature on Sirente

Ormo, J., Rossi, A. P., Komatsu, G. (2002) The Sirente crater field, Italy. Meteorit. Planet. Sci., V. 37, No. 11, 1507-1522. Link to abstract

Ormo, J., Rossi, A. P., Komatsu, G., Marchetti, M., De Santis, A. (2002) The discovery of a probable well-preserved impact crater field in Central Italy. Lunar and Planet. Sci. Conf, XXXIII. Link to pdf file

Ormo, J., Rossi, A. P., Komatsu, G. (2001) Sirente: a possible small impact crater in Italy. Suppl. Meteorit. Planet. Sci., 36, A54.

Ormo, J., Rossi, A. P., Komatsu, G. (2001) The Sirente structure, a possible well preserved Holocene impact crate in the Appennines, Italy. Impact markers in the stratigraphic record. Sixth ESF-IMPACT Workshop, 83-84.

Santilli, R., Ormo, J., Rossi, A. P., Komatsu, G. (2003) A catastrophe remembered: A meteorite impact of the 5th century AD in the Abruzzo, central Italy. Antiquity, 77, 296.

Ormo, J., Rossi, A. P., Komatsu, G. (2002) The discovery of the Sirente Crater Field. Tumbling Stone, 18, Spaceguard Foundation and NEODyS. Link to article


Useful links

Contacts

For information on the Sirente crater field and related activities at IRSPS please contact:
Angelo Pio Rossi
IRSPS
Universita' d'Annunzio
Viale Pindaro, 42
65127 Pescara, Italy
Tel: +39-085-453-7506
Fax: +39-085-453-7545
e-mail: arossi@irsps.unich.it.
Goro Komatsu
IRSPS
Universita' d'Annunzio
Viale Pindaro, 42
65127 Pescara, Italy
Tel: +39-085-453-7507
Fax: +39-085-453-7545
e-mail: goro@irsps.unich.it.
Jens Ormo
Centro De Astrobiologia
INTA
C. de Torrejon a Ajalvir
Torrejn de Ardoz, Madrid
Tel: +34-91-520-1936
Fax: +34-91-520-1621
e-mail: ormo@inta.es.
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