The eruption affected wheather in Europe for at least a year during and after the eruption. Kristin Martha Hakonardottir Dear Kristin, 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. 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.