To determine if there were a correlation between undersea earthquakes and the El Nino phenomena, I executed a query excluding Richter 5+ earthquakes and earthquakes deeper than 50km in the El Nino area of the Pacific from 1970-2000, since stronger and deeper earthquakes rarely indicate volcanic eruptions. This seems reasonable to me, since we're looking here for a connection between volcanic eruptions and El Nino. This very interesting graph shows earthquakes in the area east of Indonesia, where El Nino originates. The graph shows extreme peaks in 1982 and 1995-98, that correlates with the 1982-83 and 1997-98 extreme El Ninos. From this I conclude that the idea of El Nino being caused by under sea volcanoes is correct.
Offered by Kiko.