Subject: Formation of Kaneohe Bay and Ko'olau Cliffs on Windward O'ahu

I have heard that Kaneohe bay may have been the crater for the volcano which formed the Ko'olau range, and that this section of the island dropped into the sea creating the steep cliffs above Kaneohe. Is this correct, and can you give me a brief summary of the geologic history of the Ko'olau and how these magnificent cliffs were formed?

    Yours is a fasinating story for the origin of Kaneohe Bay (which is off of northern-eastern O'ahu in the Hawai'ian islands) but it is only somewhat correct. The area near Kaneohe bay was once a crater but it filled in with lavas and rock debris over a million years ago. The Bay we see now is not related to a volcanic crater.
    After this crater filled in, much of the windward side of Oahu (the eastern side of the Ko'olau) dropped into the ocean in a giant landslide. The debris extends for hundreds of miles north and east of the island. However, this slide did not cause the Pali. My interpretation of how the Pali formed comes from looking at photos of the island (of O'ahu) and living on the Honolulu (western) side. In the back of the valleys on the Honolulu side, there are steep cliffs between the valleys are ridges. If these ridges were to continue to erode away, the cliffs in the back of the valley would merge together to form a giant wall (which is essentially what the windward Ko'olau cliff is). If you look at the windward side from the air, you would see low ridges extending from the Pali towards the ocean. These low ridges are the eroded leftovers of the ridges we see on the Honolulu side (e.g., St. Louis Heights or Waahila Ridge).
    For addional geologic information on this subject, the best book to look in is 'Volcanoes in the Sea' by G. A. Macdonald and others.

Dr. Mike Garcia, Professor of Geology
Department of Geology and Geophysics
University of Hawaii, Honolulu, HI 96822

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