by Dr. David Kring
The energy of the impact event melted some of the target rocks, and dispersed those melts in the form of small droplets and melt splashes around the crater. Melt was produced from all four types of rock seen in the walls of the crater, plus the impacting asteroid. The melt droplets are often vesicular, indicating gases were escaping the melts while they were flying through the air and solidifying.
The four types of rock in the target sequence that were melted are, from top to bottom: 6 to 30 feet-thick red Moenkopi siltstone, 260 to 265 feet-thick Kaibab dolomite and sandstone, 10 feet-thick Toroweap sandstone and dolomite, and 700 to 800 feet-thick Coconino sandstone.
The melts produced from these rocks were not mixed well, and therefore the melt droplets show a variety of compositions. Fred Horz, David Mittlefehldt, Tom See, and Charles Galindo recently (in 2002) found that some of the melt seems to have been produced near the surface of the impact site, because it is a mixture of 55% Moenkopi, 40% Kaibab, and 5% meteorite. The scientists estimated that this melting occurred in the upper 100 feet of the impact site. Other melts in their study seem to have formed from much more Kaibab (50-70%) and entrained more of the melted asteroid (15-20%). These melts could have formed in the same shallow interval, but could also have formed more than 270 feet below the target surface.
Because the melts were made from dolomite, a lot of the gas that produced the vesicles in the melt droplets was probably carbon dioxide. Calculations by David Kring indicate the amount of carbon dioxide released to the atmosphere was not, however, large enough to affect the climate. Steam was another gas that was probably produced by the impact event.
The amount of melt produced by this impact event was small. The melt was also ejected from the crater quickly, preventing thorough mixing of the melt produced from each of the target rocks and asteroid. A larger impact event, in contrast, will produce a much greater volume of melt. In larger impact events a greater fraction of the melt will also remain in the crater, producing a melt sheet with a much more homogeneous composition than the melt droplets at Barringer Meteorite Crater. Impact melt at a larger crater will also have a smaller contribution from the impacting asteroid. Generally, only traces to perhaps 1% of the melt comes from the impacting asteroid in larger impact events.
Hand Built for maximum Impact by The Cyrus Company. 1998.