Diamond Head is the name of a tuff cone on the Hawaiian island of O'ahu and known to Hawaiians as Leahi (photograph at right). Its English name was given by British sailors in the 19th century, who mistook calcite crystals embedded in the rock for diamonds.

Geology

Diamond Head is part of the complex of cones, vents, and their associated flows that are collectively known to geologists as the Honolulu Volcanics, which are part of the much larger Koolau Volcano (known to most people as the Koolau Range). The Honolulu Volcanics is a series of volcanics that created many of Oahu’s well-known landmarks, including Punchbowl, Hanauma Bay, Koko Head, and Manana Island in addition to Diamond Head. Diamond Head, like the rest of the Honolulu Volcanics, are much younger than the main mass of the Koolau Mountain Range. While the Koolau Range is about 2.6 million years old, Diamond Head is estimated to be about 200,000 years old.

The eruption that built up Diamond Head was probably very brief, lasting no more than a few days. It was probably explosive, since when the cone was originally formed, the sea level is thought to have been higher and the vent burst erupted over a coral reef. Another factor probably contributing to the eruption’s explosive nature was that rising magma would have come into contact with the water table. The eruption’s relatively brief length is thought to explain why the cone today is so symmetrical.

A nearby eruption that took place at about the same time (probably after) as the Diamond Head eruption was the eruption that built the Black Point lava shield.

Since the type of eruptions that built Diamond Head tend to be a one-time-only event, geologists don’t believe Diamond Head will erupt again.

Diamond Head in Local Culture

Diamond Head cone seen from a Waikiki Hotel

It is located on the coast east of Waikīkī (in Honolulu) and is a defining feature of the view known to residents and tourists alike. A symbol of worldwide recognition, it is not surprising that the name Diamond Head is widely exploited for commercial purposes (see disambiguation page). The volcanic cone is a State Monument. A popular trail and stairway lead from the interior of the crater to lookouts along the rim.