Mount Zao Okama Crater Lake (Emerald Volcanic Caldera)

Category: Spectacular Volcanic Crater Lake & Scenic Alpine Drive | Location: Togatta Onsen, Zao Town, Katta-gun, Miyagi Prefecture

Resting high upon the volcanic spine of the Zao Mountain Range at an elevation of 1,600 meters along the border of Miyagi and Yamagata Prefectures, the Okama Crater Lake (Zao no Okama) stands as one of Japan's most awe-inspiring alpine geological wonders. The name 'Okama' derives from its uncanny circular resemblance to a traditional cast-iron Japanese cooking cauldron (kama). Ringed by the stark, mineral-scorched volcanic precipices of Mount Kattadake, Mount Kumanodake, and Mount Goshikidake, the crater presents an unforgettable visual contrast between rugged, desolate volcanic rock walls and the serene, jewel-toned waters cradled within. Measuring approximately 325 meters in diameter and plunging 27 meters deep, the crater pool is filled with intensely acidic water (pH approximately 3.5) saturated with dissolved sulfur and copper salts, entirely preventing any aquatic plant or fish life from colonizing its depths. The defining marvel of Okama is its mesmerizing optical chameleon effect: the water shifts constantly across a spectrum of vibrant shades—ranging from vivid emerald green and jade to luminescent turquoise and deep cobalt blue—governed by the angle of sunlight, seasonal temperature inversions, and drifting alpine cloud cover, earning it the affectionate moniker 'Goshikinuma' (Five-Color Pond). Travelers reach the summit observation decks with exceptional ease via the scenic Zao Echo Line and Zao Highline toll highways, which traverse subalpine forests from late April through early November before closing for the subarctic winter. When the highway first reopens in late April, motorists drive through dramatic towering snow corridors (Yuki no Otani) carved through meters-deep drifts. From the panoramic lookouts near Kattamine Shrine atop Mount Kattadake, visitors savor crisp mountain breezes while gazing down upon the gleaming emerald crater, frequently set against spectacular seas of undulating clouds rolling over the valleys below.