Re: dry Meditteranean

From: Aidan Karley (aidan_at_mynameplus1.demon.co.uk.invalid)
Date: 01/18/05 

Date: Tue, 18 Jan 2005 16:00:07 GMT

In article <A_KdnbZ9-rfYJ3HcRVn-qw@is.co.za>, Frank Scrooby wrote:
> What happens if Gibraltar is blocked and Mount Vesuvius (spelling probably
> not right - Volcano in Sicily - Pompeii) goes into semi-permanent eruption.
>
       Vesuvius is the volcano that totalled Pompeii, just outside Naples,
about half-way "up" the Italian peninsula; Etna is the volcano on Sicily.
       
> I don't know if the volcano has the lava reserves for this but what if it
> starts behaving like the volcano chain in Central America or like the
> Hawaiian chain?
>
       There is one volcano on the Big Island which has been in a long,
relaxed eruption for the last half century or so (Kiluea, or something not
dissimilar), but the total volume of lava is not huge (anyone got any
figures? a cubic km or so?); eruptions along the Andes/ Central America/
Rockies/ Aleutian/ Kamchatka/ Japan/ (...) chain of volcanos is more-or less
continuous, but if you restrict your attention to moderate spans (say, 500km)
it is discontinuous on the decadal time scale.
       
       I'm guessing that you normally post in rec.arts.sf.science, not
sci.geo.geology (no disrespect - asking questions is the best way to clear up
lack of information).

> Assume there is a new eruption every year or two. The lava heads down hill
> into an increasingly saline sea. Big sizzle-pop-bang when hot lava meets
> cold water. Much evaporation.
>
       Shades of the oft-seen clips of (basaltic) lava running into the sea
off Hawaii, forming "pillow" structures etc. Impressive, isn't it. That the
(generally) live cameraman who filmed these close up wasn't broiled is a good
illustration of the abnormally high specific latent heat of evaporation of
water, which is a consequence of it's strong hydrogen bonding. (It also
illustrates the relatively low spec.lat.ht.fusion of silicate melts, and that
the melts don't do a lot of crystallisation in these circumstances, so don't
get to release their spec.lat.ht.crystallisation either.) The actual volume
of water evaporated by lava flowing into isn't particularly large, compared
with the amounts evaporated by the action of sunlight over thousands of
square kilometers of sea surface. My gut feeling is that the impact of lava
on the postulated evaporation of the Mediterranean is not going to speed
things up significantly over the Med as a whole. When you get down to the
small final "bittern" salt pools on a halite plain, you're in a different
arena, but remember that there's not a lot of reason to expect the volcano
locations to move to follow the shrinking shoreline, so *most* of the lava is
going to freeze solid long before it approached the final deeps.
       Your point about an *increasingly* saline sea is interesting though. I
*think* that the natural experiment is carried out in a number of locations -
running lava out onto the salt flats in the high Andean deserts around Lake
Titicaca (-69d E, -15d N), and comparable situations in the East African Rift
system in southern Ethiopia. The EAR has some interesting lava chemistry, but
that's from much deeper sources than surface contamination.
                

-- 
 Aidan Karley,
 Aberdeen, Scotland,
 Location: 57°10'11" N,  02°08'43"  W (sub-tropical Aberdeen), 0.021233

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