Oahu's prominent promontory evokes our island home to people everywhere

It started out with a bang. No kidding. Hot, molten lava was extruded upward through faults and channels in the Earth's mantle until -- ka-boom! -- it contacted sea water, close enough to ocean level for a pyroclastic cake bake. The resultant explosions tossed out a ring of sizzling "tuff" rocks that compacted and built up a ring on the flank of the Koolau shield volcano.

And then the rains came. Water sculpted not just the Koolaus, but also created the prow-high landmark that anchors the southernmost tip of Oahu. Sailors, excited about the glittering rock that made up the peak, dubbed the volcanic crater Diamond Head, but the gleam is only calcite crystals. Ancient Hawaiians apparently knew better and avoided the dust-bowl interior; travel writings in the 19th century mention dozens of skeletons simply dumped inside the bowl. They called it Le'ahi after the distinct forehead shape of the yellowfin tuna.

But ancient Hawaiians didn't have a travel industry. The shores of Waikiki became a haven for Hawaiian royalty, and then for vacation homes and municipal parks, and before you knew it, there were mighty hotels springing up. And they all did so in the brooding shadow of Diamond Head, a kind of landscape mnemonic, an instantly recognizable shape.

Diamond Head is a kind of logo for Hawaii, said artist Pegge Hopper. "The sheer shape of it is so iconic. A great crutch for beginning artists; if you had to ship out a label for anyone. Diamond Head, a hula girl, plumeria lei, a coconut tree -- mix them together in any combination, and you have a logo that's distinctly Hawaii."

Diamond Head's visual prominence also benefits from Hawaii's weather, said Hopper. The clear air and low clouds set off the shape the way a frame promotes a picture. "In Hawaii you see sharp, dense shadows and sparkling highlights on the landscape, and that helps define it as well."

Government-owned, Diamond Head served over the years as a training ground and revetment for the military, rarely open to the public except during occasional music festivals. That has changed, and the two-hour hike to the 760-foot summit has become one of the most popular outings in the islands.

On the rim, visitors can also inspect the tunnels and sighting apertures dug out by the Army, when the peak was an important part of Fort DeRussy's artillery system.

Diamond Head is also the name of a British heavy metal band and of a Charlton Heston movie, of a comic-book villain and of a tiny Southern hamlet. But our Diamond Head is simply the best-known volcanic crater in the universe. So there.

» To visit: Diamond Head State Monument is open from 6:30 a.m. to 6 p.m. daily. It costs $1 to walk into the crater or $5 to drive a car and park. If you hike the trail to the summit, take water and a flashlight, as you'll have to pass through some military tunnels. Call 587-0285.