Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!ukma!rutgers!att!cbnews!henry@zoo.toronto.edu
From: henry@zoo.toronto.edu (Henry Spencer)
Newsgroups: sci.military
Subject: Re: Largest Bomb dropped
Message-ID: <5199@cbnews.ATT.COM>
Date: 29 Mar 89 03:21:10 GMT
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From: henry@zoo.toronto.edu (Henry Spencer)
>     I 'heard' (ie totally unsubstantiated) that this 'propane' bomb created
>     a very distinct 'mushroom shape' cloud - and that the Air Force was
>     told not to use it anymore in Vietnam - for obvious reasons.

I can't answer on the latter part, but any big, hot explosion near ground
level will create a mushroom cloud.  The hot fireball tends to rise, being
lighter than air.  Air drag and cooling due to mixing will slow it, but
mostly around its periphery.  This tends to reshape it into a doughnut-
shaped vortex, with the internal circulation moving down on the outside
and up on the inside.  The rise of the fireball plus the extra upward
motion at its center pulls the stalk of smoke and debris upward beneath it.
Large charges of conventional explosives will give a small, brief mushroom
cloud.  It's entirely believable that fuel-air explosions would too.

                                     Henry Spencer at U of Toronto Zoology
                                 uunet!attcan!utzoo!henry henry@zoo.toronto.edu