Inside the Deep Caves Carved by Lava

Centuries of eruptions on the Big Island have created hidden networks of passages beneath volcanoes.

In December 2016 a large lava delta formed by Kilauea volcano sank into the sea, exposing the mouth of a lava tube. A lava delta is created when molten rock reaches a flat area and spreads out in multiple directions like a fan. After this lava delta collapsed, new lava spewed from the tube like a fire hose into the ocean 60 feet below.

Veteran cavers Peter and Ann Bosted were cruising around their hometown of Hawaiian Ocean View, on Hawaii’s Big Island, a few years ago when Ann spotted a small hole off the side of the road.

It was no more than three feet wide—just big and inviting enough for the couple to pull their car over and try to slink into.

“We had a couple hours to kill,” Peter told me, “so we started surveying, and we found a side passage that turned out to be a lot more mazy than we expected.” Back home, Peter marked the puka, or cave entrance, on a digital map and planned to return later—with the landowner’s permission—to see where the opening might lead.

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