Diamond Head

The volcanic tuff-cone crater rising behind Waikiki Beach, Hawaii's most recognisable skyline.

Hawaiians call it Lēʻahi. The name most likely joins words meaning "brow" and "tuna", because the ridge looks like the back fin of a tuna fish. Diamond Head is a tuff cone: a hill made of volcanic ash that settled and hardened into rock called tuff. Today it is protected as Diamond Head State Monument, and since 1968 it has also been a U.S. National Natural Landmark. More than 3,000 people a day hike to its summit.

How it formed

Diamond Head was made by a single, explosive eruption that threw ash and tiny bits of rock into the air. As they fell back down, they cemented together into tuff and built a wide, saucer-shaped crater. Hawaii's state parks say this happened about 300,000 years ago, while other scientific estimates put it at 400,000 to 500,000 years ago. Either way, it is much younger than the Koʻolau mountains behind it, which are about 2.6 million years old.

Why is it called Diamond Head?

In 1825 British sailors spotted sparkling crystals in the rocks and sand near the crater and thought they had found diamonds, so they named it Diamond Hill. The crystals were really calcite, a common, shiny mineral. Later the name changed to Diamond Head, "head" being short for headland, a point of land sticking out into the sea. Locals also call it Kaimana Hila, a Hawaiian way of saying "Diamond Hill".

Hiking to the top

The summit trail was built in 1908 as part of Oʻahu's coastal defence system. It is about 1.3 kilometres long and climbs roughly 170 metres from the crater floor, with switchbacks, steep stairs and a lit tunnel about 70 metres long. At the top is a Fire Control Station, finished in 1911, that once directed army guns. From there you can see the coast from Koko Head to Waiʻanae, and in winter you may spot humpback whales. A lighthouse built in 1917 stands on the outer slope.

On the globe

The model shows the broad volcanic crater with its sharp ridge rising above the Honolulu shoreline. Zoom in to see the bowl-shaped crater floor inside the ring of cliffs.