Tsunami experts believe a bomb secretly tested off the coast of Auckland 50 years ago could be developed to devastating effect.

University of Waikato researchers believe a modern approach to the wartime idea tested off Whangaparaoa could produce waves up to 30m high.

Dr Willem de Lange, of the Department of Earth Sciences, said studies proved that while a single explosion was not necessarily effective, a series of explosions could have a significant impact.

"It's a bit like sliding backwards and forwards in a bath - the waves grow higher," Dr de Lange said yesterday.

He was responding to a Weekend Herald report of experiments at Whangaparaoa in 1944-45 to create a tidal wave bomb. The top-secret work by the late Professor Tom Leech was detailed in 53-year-old papers released by the Ministry of Foreign Affairs and Trade.

Dr de Lange said a coastal marine group from the university recently studied the likely impacts of underwater volcanic explosions.

Their work concluded that the next eruption in the Auckland region was likely to be under water, given the large amount of water around the city.