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Towada-Hachimantai NP, Iwate
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Hachimannuma fills 11 craters linked east–west, so its single water surface hides a whole chain of volcanic pits. The crater lake formed about 7,300 years ago and has a 1.5-kilometer circumference.
The bog around Hachimannuma holds peat 2.1 meters thick; monitoring estimates it began forming about 5,000 years ago. The lake is older, so wetland has slowly built up around its rim.
Winter winds heap snow behind the plateau, and meltwater feeds the wetland around Hachimannuma from April into June. Spread gently over shallow slopes, that water helps peat accumulate instead of washing away.
The Environment Ministry lists Hachimannuma among Hachimantai’s important wetland sites. Across these high ponds, it records mountain insects including Mutsuakane and Kaojiro-tonbo dragonflies and Chishima-mizumushi water bugs.
Near the pond, trampling once left patches of summit wetland bare. Restoration began in 1993; park volunteers use vegetation mats and native seeds, but the original wetland plants can take decades to return.
The pond’s marshes change color as flowers take their turns: skunk cabbage follows snowmelt, then primroses and cottongrass, with daylilies brightening the bog in summer. A short season brings several distinct scenes.
A local legend links Hachimantai’s Hachiman name to the early-Heian general Sakanoue no Tamuramaro, who supposedly prayed to Hachiman after admiring the mountain. The Japanese Alpine Club notes he may never have visited.
