Re: deep water = less ejecta?

[Mike Habib <habib@jhmi.edu>]

On Jan 27, 2008, at 1:50 PM, don ohmes wrote:
> Not qualitatively, according to my understanding; the heat of the  
> vapor obviously dissipates quickly relative to liquid due in part to  
> the many point sources involved. Also as the the vapor condenses it  
> extracts heat from the atmosphere.

True.  The specific heat capacity of water vapor is still quite high,  
though.  It much lower than that of liquid water (assuming standard  
pressure and temperature) but the heat capacity of water vapor is  
greater than, for example, solid silicious clay.  Your point about  
point sources for dissipation is well taken; this applies to both the  
water vapor and the vaporized rock, however.

> A jet of steam is devastating at close range, but cools quickly,  
> whereas a jet of liquid water (or molten rock) will hold it's heat  
> much further/longer...

True, but this is largely because of the mass differences: a jet of  
liquid water will usually have more mass than a jet of steam.  If the  
mass of the hypothetical jets of material are all the same, then the  
liquid water would hold the energy the longest, followed by the water  
vapor.  The particulate/vaporized rock would probably cool off the  
most quickly, though I say this with some hesitation as I do not have  
heat capacity data for molten substrates handy.  We should also keep  
in mind that the superheated ejecta would have higher heat capacity  
than at standard temperature; water vapor at 1000 K, for example, has  
a heat capacity of 2.288 kJ/kgK (compared to 1.954 kJ/kgK at 500 K).

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280-0181
habib@jhmi.edu