The Carancas event: a recent hypervelocity impact crater in the Altiplano
Tancredi, Gonzalo1; Ishitsuka, J.2; Schultz, P.3; Harris, S.3; Brown, P.4; ReVelle, D.5
1Fac. Ciencias, - Not specified -; 2Instituto Geofísico del Peru, - Not specified -; 3Dept. Geological Sciences, Brown University, UNITED STATES; 4Dept. of Physics and Astronomy, University of Western Ontario, CANADA; 5Meteorological Modeling Team, Los Alamos National Laboratory, UNITED STATES

Interplanetary material (meteoroids) continually enter the upper atmosphere of the Earth at velocities over 40,000 km/h. Due to friction with the air, the smallest particles totally sublimate in the upper atmosphere, leaving a luminous ionized trail. Larger particles (up to a few tons), produce bright fireballs that can be observed over extended areas, and they may produce audible sounds. During atmospheric entry, larger meteorites typically decelerate and fragment. In some cases, a few meteorites reach the surface at very low velocities (close to terminal speed, 100-300 m/s), producing little damage in the impacted area. Iron meteoroids with masses over a few tens of tons can reach the surface without major loss of the original mass, but weaker stony meteoroids need masses greater than several megatons in order to reach the surface at hypersonic velocities. A recent crater-forming event in the Andes Altiplano of Peru challenges that long-accepted picture of the atmosphere effectively shielding the surface from high-speed impacts by the most common stony meteoroids. On September 15th, 2007, at 11:45 AM local time, on the Southern shore of Lake Titicaca, many inhabitants saw a bright fireball and heard explosive sounds. Ten kilometres south of Desaguadero, Carancas villagers heard a large explosion and observed an expanding cloud of dust covering a large fraction of the sky. Some minutes after, they found a 15m-diameter crater at the site of the "explosion" as well as numerous blocks of near-surface sediments (<1m) dispersed over large distances. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earth's atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event.