By Dayle Turner Of the craters on Oahu, the most familiar to residents and visitors are Diamond Head and Koko Head. According to Hawaiian legend, Ka'au was formed as a result of an unsuccessful island-unification effort by the demigod Maui.
Geologists tell a different story.
In the scientific version of the genesis of Ka'au, the crater was formed by an explosive upswelling of volcanic material deep within the earth's core. In geological terms, Ka'au is classified as a tuff cone, its foundation composed primarily of compacted volcanic ash and dust. The trail to Ka'au begins in a quiet neighborhood at the end of Wai'oma'o Street on the Maunalani Heights-side of upper Palolo Valley. This locale is the domain of the Board of Water Supply and hikers must obtain permission to legally enter the area. For the first 15 minutes, the trail meanders mauka along Wai'oma'o Stream, the same watercourse where a woman was tragically swept downstream and drowned during a flash flood in 1986.