The Kohala Mountains are the most northerly and subsequently oldest volcanoes on the Big island of Hawaii. This is where the island began over the same hot spot in the Earth’s crust that has created every island from here to Wake Island, tracing the movement the Great Pacific Plate.
The Kohala, like Mauna Kea and Mauna Loa, create a barrier to moist westerly breezes. The rise in elevation, provided by the volcanic mountains, causes the clouds to lose their burden of moisture on the windward or northeast side, which is why the west side of the island tends to be slightly dryer. This continuously abundant rain on the mountains will, as these waterfalls attest over millions of years, return the great island to the ocean from which it came.