local people have been urged to move to higher ground. david tappin is a marine geologist at the british geological survey. talk to us through how unusual this particular underwater volcanic eruption is, and also the strength of it. i eruption is, and also the strength of it. ~ ., , eruption is, and also the strength of it. ~ . , . ., of it. i think that this particular event, it of it. i think that this particular event. it is of it. i think that this particular event, it is quite of it. i think that this particular event, it is quite a of it. i think that this particular event, it is quite a surprise. i event, it is quite a surprise. underwater eruptions generating tsunamis are well studied and well known. there is a classic example in 1883 in indonesia when 36,000 people died when a volcano exploded and resulted in an devastating tsunami. along the tonga margin, there have been tsunamis, the most recent in