I haven't worked much on meteorite impact craters for about 20 years, and have been delighted to find how much the concepts have changed since Chuck Simonds and I published our ideas about the role of volatiles and lithology in impacts back in 1980. The dramatic increase in our understanding results from two factors: over a half century of detailed work by (mostly) German geologists documenting the Ries in detail at all scales, and the dramatic increase in computational capacity since the 1980's. I reproduce here a figure from Stoffler et al. (2013) and a brief description of the five phases of an impact that they discuss. Strongly recommend the original papers. The impact scenario is for formation of the 24-kilometer Ries Crater in Germany, about 14.5 million years ago. It's a favorite spot for meteorite enthusiasts, not the least because in the village of Nordlingen, a church is constructed from one of the impact products, suevite!
·
Phase 1,
panel a: Impact phase, about 2 milliseconds after impact;
·
Phase 2,
panel b: Primary ejecta plume and final shape of the transient cavity;
ejecta curtain and clast-laden impact melt layer, about 10 seconds after
impact;
·
Phase 3,
panel c: fully developed primary ejecta plume, crater shape after collapse
of transient cavity; formation of central uplift, and innermost ejecta blanket,
the Bunte Breccia from deposition by the ejecta curtaint; about 40 seconds
after impact, and
Phase 3, panel d: buoyant primary ejecta plume begins collapsing, deposition of Bunte Breccia; slumping of volatile-containing sediments into the hot melt pool begins; about 2 minutes after impact
Phase 3, panel d: buoyant primary ejecta plume begins collapsing, deposition of Bunte Breccia; slumping of volatile-containing sediments into the hot melt pool begins; about 2 minutes after impact
·
Phase 4,
panel e: Secondary plume(s) formed by reaction of the hot melt pool with
water for a fuel-coolant-interaction (FCI) process is fully developed, time =
days to months;
·
Phase 4,
panel f: Collapse of the FCI-induced secondary plume(s) and early phase
deposition of outer suevite and part of crater suevite. Time = minutes to tens
of minutes after start of FCI
·
Phase 4,
panel g: late phase of secondary plume(s) and deposition of the main mass
of crater suevite-time scale of months to years
·
Phase 5,
panel h: final crater with all units in place, before formation of a crater
lake if that happens. Time – months to years after impact.
References:
Kieffer, S. and Simonds, C., The role of volatiles and lithology in the impact cratering process, Reviews of Geophysics and Space Physics, 18(1), 143-181, 1980.
Stoffler, D., et al., Ries crater and suevite revisited--Observations and modeling Part I: Observations, Meteoritics and Planetary Science 48 (4), 515-589, 2013.
Artemieva, N.A., Ries crater and suevite revisited--Observations and modeling Part II: Modeling, Meteoritics and Planetary Science 48(4), 590-627, 2013.
No comments:
Post a Comment