Lēʻahi, known globally as Diamond Head, is the iconic volcanic cone dominating the skyline of Honolulu, Hawaii. Situated at the edge of Waikīkī, this landmark draws countless visitors each year. The direct answer to whether Diamond Head is an active volcano is no; it is a remnant of a single, explosive event that occurred hundreds of thousands of years ago. The geological processes that created this feature have long since concluded.
Defining the Volcanic Status
Diamond Head is classified by many geologists as an extinct volcano, though some sources may use the term dormant. A volcano is considered active if it has erupted within the last 10,000 years or shows signs of ongoing seismic unrest or gas emissions. Diamond Head does not meet this criteria, as its last eruption is estimated to have happened between 150,000 and 500,000 years ago.
The volcano is widely considered a monogenetic feature, meaning it resulted from a single, short-lived eruptive episode. Monogenetic volcanoes do not have a sustained magma supply system and are not expected to erupt again once their initial event is over.
The lack of any current seismic activity or heat flow associated with the cone confirms its inactive status. While “dormant” implies the possibility of future eruption, the monogenetic nature of Diamond Head suggests it will never erupt again. It remains a stable geological structure.
The Unique Formation of the Tuff Cone
Diamond Head is geologically categorized as a tuff cone, distinct from the massive shield volcanoes that form the bulk of the Hawaiian Islands. Its formation resulted from a powerful hydrovolcanic eruption, which occurs when rising magma violently interacts with groundwater or seawater. This contact causes the water to flash into steam, triggering a highly explosive event that shatters the magma into fine particles.
The pulverized material, consisting of ash, cinders, and tephra, was ejected and settled around the central vent. These layers then lithified, or cemented together, into a soft rock called tuff, creating the cone’s steep slopes and wide crater. The entire process that built Diamond Head was likely very brief, possibly lasting only a few days to a month, contributing to its symmetrical shape. This rapid, explosive formation contrasts sharply with the slow, effusive lava flows that build gently sloping shield volcanoes.
Diamond Head’s Place in Oahu’s Volcanic History
Diamond Head is a product of the Honolulu Volcanic Series (HVS), a secondary phase of volcanism on the island of Oʻahu. This series began long after the Koʻolau Volcano, which formed the main eastern mass of the island, had gone dormant and was heavily eroded. The Koʻolau shield volcano is millions of years older than the features of the HVS.
The HVS eruptions created many of Oʻahu’s recognizable landmarks, including Punchbowl Crater, Hanauma Bay, and Koko Head. While Diamond Head is an extinct monogenetic cone, the Honolulu Volcanic Series as a whole is considered potentially dormant. Future, localized eruptions are geologically possible along the same rift zone, but they would likely form a new monogenetic cone rather than re-awakening Diamond Head.