Kohala is an extinct shield volcano that is located on the island of Hawaii and reaches an elevation of 5,480 feet. It is one of five volcanoes that comprise the island of Hawaii and is thought to be about one million years old, although it only emerged from the sea about 500,000 years ago. Because its last eruption is thought to have occurred about 120,000 years ago, based on studies conducted on hardened lava flows, this volcano is not thought to pose a threat to inhabitants on the island.
Because Kohala is so old, it most likely experienced the reversal in magnetic polarity that occurred 780,000 years ago. Between 250,000 and 300,000 years ago, the volcano experienced a major landslide that shortened the volcano by 3,281 feet and sent debris as far as eighty-one miles away from the shoreline. Although it is widely accepted that its last eruption occurred 120,000 years ago, lava specimens from the eastern and western sides of the volcano date to between 60,000 and 80,000 years ago. It once had two active rift zones, which is typical to other volcanoes in the area, which caused it to be active in its shield stage, which ended 245,000 years ago, and post-shield stage, which the volcano is currently in. Eruptions during these stages caused lava flows that are now layered and are known as Hawi flows and Pololu flows.
Today, the forests that have grown on the slopes of Kohala are intermingled with cones. Although the western, eastern, and southern slopes hold a low slope grade, the northern slope contains some of the highest seacliffs in the world. These cliffs are associated with the collapse that caused the major landslide and other features associated with this event include a small string of faults near the caldera. Many valleys occur along the sides of the volcano, created by water erosion and dike complexes from the many streams that flow along its slopes. The dike complexes also allow rainwater to seep through the lava into underground reservoirs, which support the inhabitants of the island.
Evidence has been found that suggests pre-modern civilizations also depended upon the volcano, including evidence of crops like sweet potatoes, bananas, gourds, and taro. Walls and steps can still be seen on its slopes, which hold some of the only remaining evidence of these cultures in the area. Some areas of the island receive an adequate amount of rainfall to grow crops, while others as close as eleven miles away receive less than five inches of rain per year. Habitats range from dry forests along the coast to cloud forests near the summit of the volcano. Because the island was isolated for so long, these types of unique habitats were able to flourish and support 155 species that are native to the island. The past isolation now poses a threat to the island, as its ecosystem cannot protect itself against invasive plant and animal species. Organizations, like the non-profit group known as The Kohala Center, have been established to help raise awareness of the importance of the island’s cultural and natural significance.
Image Caption: View north toward Kohala Volcano from the slopes of Mauna Kea. Credit: Aoi/Wikipedia