Hunga Ha'apai Underwater Cave

Pangai · Ha'apai Group · Tonga

Hunga Ha'apai is a crescent-shaped volcanic island in Tonga's remote Ha'apai Group, its steep jungle-covered slopes rising sharply from an ocean that is absurdly blue even by South Pacific standards. The island is uninhabited, its only visitors the occasional fishing boat and the rare dive charter that makes the crossing from Pangai. What draws those divers is a system of lava tube caves formed during ancient eruptions, their seaward ends now submerged and accessible from the open water while their inland extensions rise above sea level into air-filled chambers lit by shafts of light filtering through the volcanic rock and jungle canopy above. I entered the water from the dive boat anchored off the island's western shore and swam toward the cliff base. The cave mouth was a dark arch in the volcanic rock at five metres depth, roughly four metres wide and three metres tall. The water inside was even clearer than outside, the lack of plankton and surge producing visibility that seemed limitless. I finned slowly through the entrance tunnel, my torch beam catching the rough texture of solidified lava on the walls, its surface folded and rippled in the patterns frozen from the moment the molten rock met seawater thousands of years ago. After thirty metres the tunnel opened into a chamber perhaps fifteen metres across and ten metres high. The bottom was a jumble of fallen lava blocks at twelve metres depth, and between them red soldierfish clustered in dense groups, their large dark eyes reflecting my light. A painted crayfish backed into a crack, its ornate purple and white patterning looking almost artificial against the dark volcanic rock. Above me the ceiling rose to an air dome, and when I surfaced inside, the sound changed completely: the rhythmic breathing of my regulator gave way to the drip of water, the distant crash of waves outside, and birdsong filtering down from the jungle.