Diamond Head State Monument in Oahu

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Diamond Head is one of the most popular attractions in Honolulu because of its fascinating geological origin, ancient history, military past, and a hiking trail to the summit with commanding views of the ocean and surrounding area.

There is a Hawaiian hot spot located 900 miles deep under the ocean floor which is responsible for the creation of the Hawaiian Emperor volcanic chain: the seamounts, which had already submerged under the surface of the ocean and eight existing islands, including Oahu. When the hot spot becomes active, magma breaks out through the cracks and fissures on the ocean floor and slowly builds a volcanic cone. Continuous eruptions add layers over layers of basaltic rocks until it breaks the surface of the ocean and as a result, a new island is born.


The Pacific tectonic plate moves to the northeast at a speed of three inches per year, pulling an island away from the hot spot. As a result, all volcanoes on the island become extinct. Due to erosion and its weight an island gradually sinks. The first and the oldest volcano island in the Hawaiian Emperor volcanic chain is Mejii. It was once an island but is now a submerged seamount. It is about 80 million years old and it is close to Kamchatka peninsula, Russia. Kauaii is about 5 million years old and the Big island Hawaii is less than a half million years old. Hawaii is right on the top of the hot spot and has three active volcanoes and one dormant volcano. The work of Hawaiian hot spot is always in progress and now it is working on creating of a new island called Loihi, which is a seamount so far. It’s located just southeast of the island of Hawaii.

The island of Oahu was formed about 3 million years ago after the eruptions of two shield volcanoes from the bottom of the ocean. Shield volcanoes got their name because of the eruption of low viscosity magma, which is highly fluid. These create mounts resembling a warrior’s shield. When these two shield volcanoes erupted and the island Oahu emerged, the Wai’anae and Ko’olau mountain ranges were formed.
Diamond Head, or Le’ahi in the Hawaiian language, was formed during a single but powerful eruption in the Ko’olau range about 300,000 years ago. During the eruption, magma hit the water and an almost symmetrical tuff cone was formed. The wind blew ash and fine particles from the explosion which were cemented together forming a tuff rock. Trade winds were blowing from the northeast so that the southwest rim of the crater is the highest.
Le’ahi in Hawaiian language means the “brow of ahi.” In fact, the profile of the mountain resembles the head of an ahi tuna. Polynesians, who sailed in their canoes and settled on Hawaiian Islands about 1,500 years ago, gave the mountain its name. There is another translation of Le’ahi: “fire headland.” Navigational fires were lit by ancient Hawaiians on the rim of the crater to help canoes navigate the shoreline waters.
Hawaiians considered Le’ahi a sacred place. According to their beliefs, it was a resting place of the goddess of fire Pele and her sister Hi’iaka. The crater was also referred as the place of Pele’s residence so that nobody ever lived there. However, heiau or temples were built on the rim of the crater, dedicated to the god of wind La’amaomao to keep the fires protected from strong updrafts. Nowdays Diamond Head Lighthouse, built in 1917, assists with navigation of the shoreline. Its range is 17 miles.

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Le’ahi got its English name Diamond Head from the sailors of Captain Cook’s expedition in 1774. They mistook calcite crystals in the rocks of the mountain for diamonds.

The military history of Le’ahi is hardly less exiting. The Hawaiian Islands were annexed by the U.S. in 1898 and became a U.S. Territory in 1900.

In 1904 Diamond Head and the surrounding area was purchased by the U.S. Government for military use. Fort Ruger was built.  It included two tunnels, five batteries, a gun range, and a Fire Control Station. The batteries were built on the slopes of Diamond Head and the Fire Control Station was built on the summit. It coordinated and directed fire from Battery Harlow at Fort Ruger and Batteries Randolf and Dudley at Fort deRussy in Waikiki.  The Fire Control Station has four levels for observation.  It also has plotting rooms, which had sophisticated instruments to calculate the trajectory of the fire. The Fire Control Station was camouflaged by rocks and cement. In building this engineering marvel, mules were used to pull construction materials halfway and then a winch and a cable were used. No shots were ever fired from the batteries during WWI and WWII and all guns were removed by 1950th.

The crater of Diamond Head is about 3520 feet in diameter and is 760 feet high. The hiking trail starts at the bottom of the carter. It’s a combination of paved and unpaved switchbacks, a 225 feet long tunnel, steep stairs, and lookouts with benches. The summit offers stunning views of the ocean, the city, Waikiki beach and surrounding mountains.

Diamond Head State Monument has a visitor center, an interpretive kiosk, a retail store and facilities. Entrance fees are $5 per car and $1 per pedestrian paid in cash only. There are no facilities on the summit. Bring plenty of water, use sunscreen and enjoy your hike!

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