As lava from Kilauea flows to the sea, it forms a ‘shelf’ that eventually breaks off and slides underwater down the steep slopes. The whole southeast coastline of the Big Island has a giant crack and cliff where the land area below Kilauea is sinking into the sea. That whole wedge could break sending hundreds of square miles of land into the ocean. The resultant Tsunami would reach Honolulu some 200 miles distant in a mere 20 minutes… with a 100 foot wall of water.
And yes, there is an undersea ‘seamount’ eruptive cone named Loihi that is slowly building. Estimates are in 10,000 years it will finally break the surface and become a new island just a few miles south offshore… depending on what happens with the wedge break above.
When Kilauea first became active again in 1983, the TV stations contracted with independent Kona videographer Mick Kalber to get us video of the volcano action. Mick has made a career of shooting volcano video and documenting the volcano. You can see his works here:
http://www.tropicalvisions.com/