by: Charles O’Dale
IMPACT CRATER/STRUCTURE IDENTIFICATION – Geologic confirmation for an impact event:
- – GEOMORPHOLOGY – One of the first indicators of a possible impact site is “circular geology”.
- ELOCITY OF IMPACT (earth) – On earth the lowest impact velocity with an object from space is the gravitational escape velocity of 11 km / sec. The highest velocity impact is more than 70 km/s:
earth escape velocity [11 km/s] + sun escape at the earth’s orbit [30 km/s] + earth’s orbit velocity [30 km/s] = ~70 + km/sec.
The average earth impact velocity is 17 km/s.
At these speeds, impacts produce shock waves in solid materials. Both meteorite and target rocks are compressed to high density, then rapidly depressurized and exploding violently. Since craters are caused by explosion they are always circular with only very low angle impacts causing elliptical craters.
- CRATER IMPACT AGE vs EXTINCTION EPOCH
- CRATER FORMATION – Impact involves the transfer of massive amounts of energy to a relatively small area of the Earth’s surface, in an extremely short period of time (Kinetic energy). Three stages of crater formation:
– contact & compression;– excavation; and– modification.
- CRATER CLASSIFICATION – On this planet, impact craters are divided into three basic morphologic subdivisions:
– simple craters;– complex craters; and– peak ring craters.
– introduction– meteorite categories;– dating meteorites;– meteorite glossary; and– reference.
- CANADIAN CRATERS – Documented in 1967 & 1975.
- 2019 UPDATES
- UPDATE ARCHIVES
Osinski G. The Geological Record of Meteorite Impacts Canadian Space Agency 2018
ANN M. THERRIAULT – RICHARD A. F. GRIEVE – MARK PILKINGTON The recognition of terrestrial impact structures Natural Resources Canada