Dozens of hammerhead and silky sharks were filmed swimming around in extremely hot, acidic water inside the caldera of the Kavachi volcano in a lagoon in the country's west.
The expedition leader, Brennan Phillips, says the scientists were expecting to find very little life in the harsh water conditions.
"But we saw all the big sharks that were in there. So that was a total surprise and it just kept coming. You know, there's dozens of them and they are quite large.
