The Formation of Lake Onami-ike
The Kirishima Mountain Range of southern Kyushu is home to over 20 volcanoes, including the larger Mt. Karakuni and Mt. Takachiho. These volcanoes resulted from a great number of eruptions that took place over hundreds of thousands of years. The waters of Lake Onami-ike sit in the crater created by one of these huge volcanic blasts.
Originally a relatively small volcano, Lake Onami-ike acquired its current form as the result of an eruption that took place approximately 45,000 years ago, predating Mt. Karakuni, Mt. Takachino, and many of the area’s other volcanoes. So large was the eruption that the pumice and ash ejected from the volcano spread as far as the Miyazaki Plains approximately 50 kilometers to the east, where a 20-centimeter layer of volcanic debris rained down.
The magma expelled from the Lake Onami-ike volcano piled up around the crater, creating the shape of the mountain as it is today. Post-eruption, the crater filled with groundwater, forming the highest crater lake in Japan at 1,412 meters above sea level.