On our May 2026 WAZA & Friends visit to northern Japan and Hokkaido, one place was named by everyone as a highlight: the Oirase Gorge in Aomori Prefecture. It is a corridor of lush forest beside a river of fast, startlingly clear water, and its making is tied to the geology of Japan itself.
A young, restless land
The Japanese archipelago stretches more than 3,000 km, from subarctic waters in the north to subtropical islands south of Okinawa. That is a little less than the distance from Cape Town to Kinshasa. It is a country about a third the size of South Africa, yet home to some 124 million people, roughly double our number. The land is narrow, with no point more than about 150 km from the sea, and about three-quarters of it is mountainous and forested, so cities, people and farming are pressed onto the coastal plains and river valleys.
Japan sits where four of the world's major tectonic plates meet, and for millions of years they have ground, collided and slid beneath one another, buckling the land into mountains. Those mountains are young in geological terms, on the order of fifteen million years, perhaps twelve times younger than the Drakensberg. Young mountains make fast rivers: the water drops steeply, carves narrow gorges, and carries sediment down to the plains. The Oirase Gorge is one result. Lake Towada, at its head, is another, a deep double caldera formed by two overlapping volcanic eruptions.
How the gorge formed
About 760,000 years ago, volcanic activity in this region laid down thick layers of pyroclastic material across the plateau. As it cooled and fused under its own weight it became welded tuff, a dense and very hard rock. Draining southward from Lake Towada, the Oirase River cut down through this rock when the rim of Lake Towada's caldera breached and a catastrophic flood tore out the deep valley roughly 15,000 to 12,000 years ago, carving the gorge our group of South Africans walked in May.
The geology is legible in the walls. The welded tuff shows both tabular jointing, the flat horizontal fractures formed as the rock cooled from above, and columnar jointing, the angular vertical columns formed as it contracted. It is one of the few places in Japan where both appear in the same section, which is part of why the gorge is a designated natural monument.
Moss doing the quiet work
Welded tuff is almost inhospitable to plants, holding no real soil. Yet the gorge carries a mature deciduous forest of beech, katsura, tochinoki, sawagurumi and hornbeam, and the reason is moss. More than three hundred kinds of moss blanket every surface that is not moving water, and over centuries they have built soil on bare rock, millimetre by millimetre, trapping organic matter and holding moisture until trees could follow. The remarkable clarity of the stream owes much to that slow filtering through generations of accumulated moss.
The Oirase is the only outlet of Lake Towada, so every drop that leaves the lake passes through this single fourteen-kilometre corridor, cold and quick with snowmelt in May. The sound changes at every bend, from a murmur over smooth stones to the low roar of the Ashura Rapids, named for a fierce guardian figure of Buddhist tradition.
Walking it
The trail follows the water for its whole length, with only about two hundred metres of descent across fourteen kilometres. It is genuinely flat, so each person in the group could decide how far to walk, with our two coordinators, Botha and Toast, moving between them to be sure everyone was comfortable with the distance. It made for an unhurried morning, and afterwards everyone named it their favourite part of the trip.
Getting there
Oirase Gorge lies within the Towada-Hachimantai National Park and is most easily reached by JR bus, or by rental car. From Tokyo, take the Tōhoku Shinkansen to Hachinohe or Shin-Aomori, and then the JR bus toward Lake Towada: the Oirase-go from Hachinohe, or the Mizuumi-go from Aomori and Shin-Aomori. The ride to the gorge takes roughly one and a half to two and a half hours, and the buses are covered by the Japan Rail Pass. Services run from about late April to mid-November and are suspended in winter, and they are infrequent, so it is worth planning around the timetable.
You can get a rental car around Shin-Aomori station if you wish to combine the shinkansen with a self-drive option.
The most comfortable way to walk the gorge is the way our group did. We stopped Ishigedo rest stop and walked approximately nine of the full fourteen kilometres upstream towards Lake Towada. The full route will take about four to five hours, but the stops along the route, among them Yakeyama, Ishigedo, Kumoi Falls and Nenokuchi, let you walk only the section you wish. Rental bicycles are available too, and may be returned at a different point along the path. The finest times to come are late May (like in these pictures) for the fresh green leaves, and late October, for the autumn colours.
