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SV: deep water = less ejecta?



Chicxulub did not hit in deep water. It was on a continental shelf. If
the water was 200 meters deep (which is rather a lot for a shelf sea) it
would be equal to:

2 % of the diameter of the impactor
<0.5 % of the diameter of the transient crater
0.1 % of the diameter of the final crater

Cushioning would be minimal. The main effect would be that the initial
shockwave would contain rather more superheated steam and rather less
rock vapour than for a land impactor.

The effects would be more important after the initial impact since the
sea would pour into the (initially red-hot) crater. Vast amounts of
water would be vaporized and since the water would be extremely turbid I
would expect large amounts of sediments to accumulate very quickly.

Things would be very different for a hit in really deep oceanic water,
where an appreciable part of the depth of the transient crater would be
in water rather than rock. In such cases even a fairly large bolide
might not even leave a discernable crater on the bottom. 



Tommy Tyrberg 


-----Ursprungligt meddelande-----
Från: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] För john
bois
Skickat: den 25 januari 2008 13:02
Till: dinosaur@usc.edu
Ämne: deep water = less ejecta?

OK...so the Chicxulub crater is shallow because the bolide hit in deep 
water...thus sending massive water into the atmosphere and, at the same 
time, cushioning the blow to underlying solid materials.  Do we now have
to 
downgrade the amount of re-entering ejecta and associated fire storms,
heat 
pulse, and toasting as a killing mechanism?