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Re: deep water = less ejecta?

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).



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