The crater lake on Washiba-dake in the Northern Japan Alps betrays the nature of the forces beneath, although not to us
How can a mountain with a pointed summit also sport a volcanic crater? This was the question that exercised me as we walked up the ridge towards Washiba-dake (2,924m), the Eagle Feather Mountain. Perhaps the so-called crater lake we’d heard about was just a corrie carved by some long-vanished glacier. Anyway, in a few minutes we hoped to see for ourselves.
We’d spent three days wading and walking up the Kurobe river. A passing typhoon had harassed us, but the sky had cleared overnight and, across the valley, the sun was rising over Yarigatake. For a few minutes, the summit of Washiba glowed yellow in the dawn light. Then the fogbank below us stirred into life. In minutes, the vapour surged up the slope and robbed us of our view. So we never saw Washiba’s crater, even though we walked right past it.
Fortunately, the weather was better one summer day in 1907 when Shimura Urei passed this way. Looking down from the summit, he immediately recognized the crater for what it was: "I saw a small pond below and to the south, for all the world like an eruption crater … this crater on Washiba is probably a surprise for the world."
The savants were soon on the case and proved that Shimura’s first impressions were correct. Six years later a geologist named Katō Tetsunosuke reported that the banks of the crater lake comprised two layers of lava. However, he thought that the crater was too small to be the lava’s source and was formed instead by the slumping of the molten rock as it cooled. A thin layer of ash and volcanic bombs was found scattered about, further confirming the crater’s fiery origins.
That deepened rather solved the mystery of Washiba-dake. For the mountain’s summit, just a hundred metres or so above the crater lake, is not volcanic. On the contrary, it is made of a coarse-grained granite, as we could see for ourselves even in the drifting mists. We crunched through its speckled, off-white fragments as we passed by Washiba’s invisible peak.
The fog surrounding the mountain’s split personality was partially dispelled by a later generation of geologists. The granite and tonalite body of the mountain, they say, congealed about 190 million to 170 million years ago from a deep-seated magma reservoir. Much more recently, these rocks were uplifted – we may imagine them rising gracefully from the depths like a Wurlitzer organ from the pit of an old-time cinema – and then revealed by erosion to grateful mountain-climbers. So their credentials are impeccably alpine: Mt Blanc was formed in much the same way
By contrast, the crater is a parvenu. It blew (or slumped) onto the scene a mere 6,000 years ago, as a last hiccup of the volcanic activity that wracked the nearby Kumo-no-daira tableland from about 300,000 to 100,000 years before present. Much in this account remains obscure, though, notably the source of the lavas that form Kumo-no-daira. Today, dense forest and boggy alpine meadows draw a veil over the volcanic past, but the terrain lets slip a few hints here and there. Washiba’s crater is one and another is found in the plumes of sulphurous steam that still vent from Io-zawa a few kilometres to the southeast.
Two years later, we went to Washiba again, reaching the summit in cloud and driving rain. Once more the mountain kept the secret of its crater to itself. According to the Hyakumeizan author Fukada Kyūya, the lakelet was known in feudal times as “Dragon Pond”. Somehow, we seemed to have offended the beast, perhaps by doubting the volcanic origins of his crater.
We were never able to make a third attempt but, surfing a Ginza gallery one lunch hour, I did find a woodblock print that shows the pond. In front of it, under a starry sky, two Taishō-period mountaineers are sitting round a campfire. Their antique habit and the pristine scenery call to mind Fukada’s closing words about the crater. “In that pioneering era, such unexpected discoveries were not uncommon in the Northern Alps. Today, mountaineering is much more convenient but it has lost this element of surprise and wonder.”
Nihon Hyakumeizan, in a forthcoming translation as “One Hundred Mountains of Japan”
Hyakumeizan no Shizengaku (Nishi-Nihon) by Shimizu Chōsei, Kokon Shoin 2002
Woodblock print by Yoshida Hiroshi, from Twelve Scenes in the Japan Alps series (1926), published in The Complete Woodblock Prints of Yoshida Hiroshi, Abe Shuppan