It would have to be a very powerful explosion.
Actually the island is already split and sperating according to a special that was on TV last year. All it would take would be for the volcano to activate in a certain area to make the break slide off --- this will cause the tsunami.
If you look at the undersea maps around Hawaii, you will see huge areas that were cause by these massive landslide that in turn cause mega-tsunamis.
A scientist claiming it will take a thousand years for the island to maybe fall is probably the same scientist that would have predicted no tsunamis will happen in 2004 on december 23 if asked.
PS --- On december 24 2004 an asteroid came UNDER the orbit of our man-made satellites - almost immediately there was a massive earthquake 8.4 opposite of its approach near Australia, then came the series of quakes following up and around the tectonic plate line. ---- is Krakatoa next? Then .... ???