The Calderas of Akan-Mashu National Park
Akan-Mashu National Park has been shaped by volcanic activity over hundreds of thousands of years and comprises three large calderas (vast craters formed when a volcano collapses): Akan Caldera in the southwest, Kussharo Caldera in the north, and Mashu Caldera in the northeast. Each caldera contains a namesake body of water; these are, respectively, Lake Akan, Lake Kussharo, and Lake Mashu.
Akan Caldera formed over 150,000 years ago and contains several volcanoes, including Mt. Oakan, Mt. Meakan, and Mt. Fuppushi. There are approximately 10 lakes of varying sizes within Akan Caldera, many of which were formed when these volcanoes erupted. Lake Akan, the largest crater lake in the caldera, covers 13 square kilometers.
Mt. Hakuto and the summit of Mt. Meakan offer panoramic views of Lake Akan, and several smaller lakes are visible from the summit of Mt. Oakan. Visit the southern shore of Lake Akan to see bubbling bokke (mud pools), another reminder of volcanic activity in the area.
Kussharo Caldera was created by a massive volcanic eruption that took place approximately 100,000–130,000 years ago. Lake Kussharo is Japan’s largest caldera lake, covering 80 square kilometers.
For panoramic views of Lake Kussharo and the surrounding volcanic terrain, hike to the top of Mt. Mokoto. Enjoy lakeside views from the Wakoto Nature Trail on the Wakoto Peninsula. This trail loops the peninsula and passes Oyakotsu Jigoku, a spot on the lakeshore where hot water bubbles at the waterline and steam escapes from between rocks.
Mashu Caldera is the youngest of the three craters, having formed approximately 7,000 years ago. Lake Mashu (19 sq km) fills the caldera to its brim and is one of the world’s most transparent lakes.
Mt. Mashu, on the eastern edge of Lake Mashu, is an ideal spot to enjoy the views of the lake and surrounding area. There are many excellent vantage points along the Mt. Mashu Trekking Trail, which follows the rim of the caldera to the top of Mt. Mashu. The summit of nearby Mt. Nishibetsu also commands fine views of the lake, and is accessible via the Mt. Nishibetsu Trekking Trail.