Hanauma Bay

Staring out at the circular-shaped shore of Hanauma Bay on the southeast tip of East Honolulu, you can imagine how this beautiful cove was once a volcanic crater. Today, this crater, likely flooded by wave erosion, is home to an important nature preserve and the island's most popular snorkeling destination.

The Hanauma Crater was created about 32,000 years ago during the Honolulu volcanic series, the latest (and perhaps final) burst of volcanic activity to occur on Oʻahu.Tens of thousands of years ago, a series of volcanic vents opened along the southeast shoreline of Oʻahu. Unlike the gentle lava flows currently building the island of Hawaiʻi, the late-stage eruptions on Oʻahu were violent explosions. The volcanic vents that formed Hanauma Crater opened on the sea floor. Upwelling magma vaporized the ocean water and steam explosions blew the magma into fine ash. The explosions built cones of ash, which solidified into tuff. The eruptions shattered the sea floor—coral reef and basalt—and scattered pieces that are now embedded in the tuff. Wave erosion eventually cut through the low, southeast wall of the crater, forming the current bay.