Tsutanuma
Tsutanuma, or Tsuta Swamp, is 1 kilometer in circumference, making it the largest of the six swamps on the trail. The swamps were created thousands of years ago when the slope of 1,298-meter-high Mt. Akakura (visible to the left) suddenly collapsed in a debris avalanche, transforming the valley landscape. Debris avalanches occur when brittle rock forms on the upper reaches of the mountain on top of a softer, more fragile base. The configuration has been described as similar to “a paperweight sitting on tofu,” and it can crumble at the slightest impact, with the avalanche reaching incredible speeds.