What are my risks?

• Oahu Volcanoes
• Is there a threat of a volcano erupting on Oahu again?
• Vog and Laze Hazards on Oahu

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Oahu Volcanoes

Oahu has been formed from two principle volcanoes: Waianae and Koolau. Waianae is about 2.2-3.8 million years old and Koolau is about 1.8-2.6 million years old. Both volcanoes are now considered extinct.

The island is also riddled in spots by smaller volcanic features such as Diamond Head, Punchbowl, Salt Lake Crater, Koko Head and Koko Crater. These smaller volcanoes formed in more recent times, although the age determinations on them are not very good. In general, these "post-erosional" volcanoes are believed to be between 70,000 and 500,000 years old.

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Is there a threat of a volcano erupting on Oahu again?

It is always possible, but the odds are extremely slim. Vulcanologists (people who study volcanoes) predict volcanic activity for places such as Oahu by looking at the area's historical record. Although data is limited, it suggests Oahu's post-erosional volcanoes erupted every couple of 10,000 years or so. Since it has been longer than that since the last eruption, it indicates volcanic activity has finished for Oahu.

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Dr. Ken Rubin, Assistant Professor
Department of Geology and Geophysics
University of Hawaii, Honolulu, HI 96822

Vog and Laze Hazards on Oahu

Although volcanoes on Oahu are extinct, volcanic hazards do affect the island. Volcanoes spew noxious plumes of acidic gases. The resulting vog and laze effect many communities across the State, including Oahu.

When a volcanic erupts, sulfur dioxide within the molten rock is converted to sulfuric acid. The resulting plume is known as vog (volcanic fog).

Gases are also produced at the ocean. When the lava enters the ocean, hydochloric acid is produced - called laze (lava haze). Both of these gases can contain particulate matter, such as volcanic glass or trace metals.

Vog and laze are carried by winds across the county. The impacts include: