(This section is under construction)
This is an idea that has been proposed by Dr. Dan Walker, recently retired from the University of Hawaii. He was able to correlate increases of seismic activity along the East Pacific Rise (a mid ocean spreading center) with El Nino events since the early 1960s. If you then make the assumption that the seismicity is due to eruptions on the spreading center, you may have a connection. His thesis is that large amounts of erupted lava will heat large volumes of water which will then rise to the surface and mess up the currents, climate, etc., thus generating an El Nino.
The idea has not been very well received by the scientific community and Scott Rowland, University of Hawaii, thinks there is some question about the timing of the two correlated events (seismicity and El Nino). El Nino events preceed the seismic swarms by a short time interval and perhaps the El Nino is triggering the seismicity! This would happen because El Nino involves minor changes in sea level at different parts of the ocean, which would be transmitted to the mid ocean ridge below as a change in pressure.