The book I read was "Island of Volcanoes"

The book that I read was about two boys, Tony and Robert,  who went in a island where some old temples. They went to an island by plane and from the island to the Island of volcanoes by helicopter. On the island they met Raul, a man who works on the island and he said that there was a temple on the island but it was vanished. After that Dad went to work near the beach and the two boys with Raul decided to go to search the vanished temple. They walked for a long time and they found an entrance. They found an entrance of a cave and they found a piece of the temple, it was enormous. They found another thing: a statue, it was fantastic. Tony toke the photos. They slept in the cave all night and in the morning Raul saw that on the entrance of the cave there were a lot of rocks. They climbed but Tony hurt his leg. They went out from the cave and they saw that fire came out of volcano. The boys' dad saw it and went by helicopter to take them. When, all together, went to the beach Robert showed them some old pieces of money, but they were gold!