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The island of Oahu was formed from two shield volcanoes, Waianae and Koolau. The Waianae volcano was
formed first, some 2.2-3.8 million years ago. Koolau, some 1.8-2.6 million years ago. Both volcanoes are extinct.
The Waianae caldera is near center of Waianae Range, on Oahu's west side.
Waianae's last eruption was 1.8 million years ago. It's eroded remnants make up the Waianae Mountain Range.
The Koolau caldera is south of Kaneohe Bay, on Oahu's east side. About half of the volcano slid into the ocean
during the Nuuanu landslides, shortly after the volcano formed. Following a period of dormancy, Koolau eruptions about
one million years ago known as
the Honolulu Volcanic Series created landmarks such as Diamond Head, Hanauma Bay and Punchbowl Crater.
Koolau's eroded remnants make up the Koolau Mountain Range.
Oahu Volcano Exploration
Diamond Head is a volcanic crater and is part of the Koolau range. It has been extinct for 150,000 years.
It's possible to hike to Diamond Head's 760 foot summit. The steep Diamond Head Summit Trail starts as a concrete walkway with
switchbacks, continues up a series of steep stairs and long, dimly-lit tunnels. The trail length is 1.6 miles with an
elevation gain is 560 feet. Anticipate that it could take 3 hours to reach the summit.
Bring water and a flashlight.
Park Brochure: Diamond Head National Monument
Oahu has a great bus system!
Depending on where you plan to go, you might not even need to rent a car to explore the island.
A shield volcano is a large volcano with a gentle slopes.
A caldera is a collapsed volcano.
In contrast to a caldera, a crater is a smaller, circular depression that is created during volcanic eruptions when
an explosion ejects rocks from the earth.