Kohala Volcano, Hawai`i

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Haleakala
Loihi

Kohala
Hawai`i's Oldest Volcano

Photo by J. Kauahikaua on August 26, 1994

Kohala Volcano is the oldest of Hawai`i's five subaerial volcanoes and probably emerged above sea level more than 500,000 years ago. Toward the end of its shield-building stage 250,000 to 300,000 years ago, an enormous landslide removed the volcano's northeast flank. Twenty kilometers wide at the shoreline, the landslide cut back to the summit of the volcano, which at the time was just over 1,000 m higher than today, and traveled 130 km across the ocean floor. The famous sea cliffs of windward Kohala shoreline mark the topmost part of the headwall of this ancient landslide.

When eruptions had built Kohala's broad shield to its greatest extent, the volcano was more than twice as wide as it is today. Based on an abrupt change in angle of the submarine slope at a depth of about 1,000 m, scientists estimate the subaerial part of the island at this time was more than 50 km wide. Then, when the rate of eruption decreased more than 300,00 years ago, the slow subsidence of the Island outstripped the rate of growth of the volcano, which slowly began to sink beneath sea level. But to the southeast, lava flows from Mauna Kea and Mauna Loa buried the southern flank of Kohala.