Although when meteorites impact the ground they sometimes produce impact pits these are not impact craters. Most meteorites that impact the ground are falling at free fall velocity after having been slowed down considerably by earths atmosphere and they do not have the energy to produce true impact craters. Impact craters are generally produced by larger multi tonne meteorites tonnes that have not been significantly slowed down by earths atmosphere and are still travelling pretty much at cosmic velocity on impact. Upon impact meteorites of this size produce shockwaves both into the ground and also into the impactor itself. These huge shockwaves instantly create huge pressures which in turn create extremely high temperatures (in the order of 10,000 degrees centigrade) These temperatures are enough to almost completely vaporize the impactor and a quantity of the impacted rock, sending them into the atmosphere into an expanding vapour plume. As the pressure waves and temperatures decrease the further into the ground they go the next layer created is a melt layer where the rock is melted. Below this the pressure is still enough to basically fragment and fracture the rock into a breccia. The pressure will also carry downwards melted rock and fragments further into the ground below the impact crater. Impacts of this nature leave behind many different impact products. Impactites, impact melts, tektites, impact glasses, impact breccias, monomict and polymict breccias, suevites, pseudotachylites, shattercones and many more are all terms used for impact related products. All these terms can be very confusing and some are often used interchangeably. I make no claim to correct usage here but hope to keep terminology and classification as simple as possible. Please see ‘Impacts and craters’ page in the ‘About meteorites’ section for more in depth information.
