You probably have the best resources for studying Laki there in Iceland so
hopefully my answers won't be too simple. There has only been a little
bit of work on the effects of lava flows entering the ocean. As far as I
can tell, at least in Hawai'i, the effects are rather small and localized.
The two main things that can happen involve the generation of littoral
explosions, the heating of the water, and the burying of the near-shore
sea bottom. Littoral explosions result from the interaction of sea water
with hot lava. They can be minor or rather explosive. Some of the
littoral explosions in Hawai'i threw 2-m sized blocks a few hundred
meters, and that involved a flow much smaller than the Laki flow. Still,
compared to a big explosive eruption littoral explosions are pretty minor
unless you happen to be nearby.
Heating of ocean water seems to sometimes kill ocean life and other times
it doesn't. I've seen movies taken offshore from Hawai'i while lava was
entering the ocean. The fish are swimming happily around, perhaps even
feasting on organisms escaping the lava. On the oter hand, lava entering
the ocean during the 1995 Fernandina (Galapagos) eruption killed hundreds
of fish, then sea birds dove into the hot water to eat the cooked fish and
got cooked themselves.
As for the subsurface, there are probably lots of bottom dwellers who
wouldn't be able to move fast enough to avoid being buried/cooked by the
lava. Their demise would most certainly be felt all up the food chain.
Scott Rowland, University of Hawaii
Kristin Martha Hakonardottir
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