NZ scientist piecing together Tonga's volcanic eruption

January's volcanic eruption in Tonga and subsequent tsunami garnered international intrigue, but a New Zealand volcanologist is the first overseas scientist allowed into the kingdom to piece together what led to such a massive explosion. When Tonga's Hunga Tonga-Hunga Ha'apai submarine volcano erupted in January, explosions could be heard as far away as New Zealand and Alaska. It is now known to be the largest volcanic explosion ever recorded - double that of the next largest, Mount Pinatubo in the Philippines in 1991. Professor of Volcanology at the University of Auckland, Shane Cronin has examined ash from the explosion, video footage and aerial images. He has a working theory that the side of the volcano collapsed, vastly expanding the already explosive interactions between magma and water. Lynn Freeman speaks to Professor Cronin who is in managed isolation in Tonga.