Posted by: tsubakuro | December 22, 2009

Glaciation of the North Alps

Anyone who has been to the Yari/Hotaka area of Japan’s North Alps will surely have noticed some of the stand-out features of the landscape, namely the great glacial cirques and the U-shaped valleys. The Karasawa Cirque is Japan’s largest, while the U-shaped valley of Yarisawa is said to be the most beautiful of Japan’s glacial valleys. When viewed from Chogatake or from the air, Yarisawa typifies a valley carved out of the mountains by the slow bulldozing force of an advancing alpine glacier.

Looking down into the Karasawa Cirque

Further evidence can be seen in this area in numerous other small cirques from Kita Hotakadake to the north western cirque below Yarigatake. There’s the treacherous arête of the infamous Daikiretto, the tarn and erratics of Hyouga Kouen – Glacier Park – moraines, and of course the eye-catching landmark of Yarigatake, a true horn or Matter horn, as it was carved out by two glaciers in the cirque above Yarisawa and two more glaciers to the north eastern and north western sides.

Yarigatake - the Matter Horn of the Japan Alps with a permanent snow field in a small cirque.

The extent of ice age glaciation does not end with the Yari/Hotaka Range, however. Evidence of glaciers, most notably cirques and U-shaped valleys, can be found throughout most of the North Alps (the Kita Alps or the Hida Range) and in the Central Alps (Chuo Alps or Kiso Range) and South Alps (Minami Alps or Akaishi Range) as well. According to a map in the book, “日本列島の20億年 ― Nihon Rettou no 20 Okunen – The 2 Billion Years of the Japan Archipelago,” glaciers existed in all three ranges of the Alps and in a small area of south eastern Hokkaido. The book, “神々のみた氷河期への旅 ― Kamigami no Mita Hyougaki e no Tabi – Trip to the Ice Age the Gods Saw,” also mentions glacial evidence in two other ranges as well (at present I don’t have the book with me so I will check out these two ranges later and update the information here). Yet even though glaciers formed and crept down from the high peaks of the three ranges of the Alps, the North Alps experienced the greatest amount of glaciation.

A cirque leading to a glacial valley with clear evidence of glacial carving of the mountain sides.

There are three reasons which most likely explain why so many glaciers formed here. The first is that the North Alps receive the brunt of cold air masses coming across the Sea of Japan from Siberia, air carrying moisture from the sea and depositing it as snow once it collides with the sudden rise from sea level to 3,000 metres.

The second reason is sheer surface area: the high mountains of the North Alps are more extensive than the Central and South Alps, having a greater number of peaks over 2,800 metres. The South Alps actually cover more surface area than the North but only the central spine of the South Alps clears 3,000 metres. The mountain ranges on either side reach only just over 2,600 metres at their maximum, and typically reach only about 2,400 or 2,300 metres. The Central Alps have only the one central spine on which only a few mountains clear 2,800 metres. The North Alps, however, have multiple chains of high mountain peaks and mountains of over 2,800 metres are typical.

The last of the three main reasons for glaciation is simply latitude – the North Alps are further north – but in the case of Japan the degree of latitude is nominal when considering ice age glaciation as the direction, temperature, and moisture content of the winter air is more important than latitude in the case of Japan.

Morning sunlight shines in on a glacier's bed.

Cirques and U-shaped valleys exist in many of the sub-ranges of the North Alps. Shiroumadake’s Daisekkei is such a glacial footprint, as are the steep eastern faces of Shakushidake and Kashima Yarigatake with their bowl-shaped basins holding perennial snow below the cliffs. The Tateyama/Tsurugi Range also sports several cirques and U-shaped gullies, the one between Fujioritake and Masagodake being the most exceptional as it is the only place in Japan where glacial ice remains (the ice at the bottom of the snow pack is cobalt blue and has the characteristics of glacial ice but it is a remnant only as the ice no longer has the mass to flow downhill). Even the Murodo Daira area of Tateyama was once the bottom of a glacier’s domain.

Some of the best examples of glaciation in the North Alps can be found on the Ura Ginza Mountains and beyond to Kurobegorodake and Kumo-no-Daira. On these mountains the are plenty of cirques to identify, particularly along the Sugorokudake/Mitsumata Rengedake route, which also offers views into the cirque where the headwaters of the Kurobe River now splash down between Jijidake and Washibadake and over to the clearly carved out peak of Kurobedake. Once one knows what to look for, the evidence of glaciers can be seen almost anywhere from around here.

Glacial cirques around Mitsumata Rengedake.

A cirque below the summit of Mitsumata Rengedake

All the evidence of glaciers in the Japan Alps is believed to be from the Wisconsin Glacial Period – the latest ice age. If there are any traces from previous glacial periods they haven’t been identified yet. One reason that there may be not traces is because the Japan Alps are relatively young ranges and it is difficult to be certain whether or not the mountains were high enough during the previous glacial period. Another more plausible reason is simply that all traces have been erased by the mountain building and weathering process.

One question is whether or not there was any glacial growth during the Little Ice Age – 1300 to 1850. The European Alps experienced two particularly cold periods when glaciers crept down from the mountainsides and devastated small villages, cutting them off from the towns below, destroying farmland and even mowing over structures. Evidence from the Southern Alps of New Zealand suggests that glacial growth there coincided with that of Europe. But what about Japan? I’d like to believe that there was some glacial ice formation in the cirque glaciers of the Japan Alps, at least the North Alps, but I have yet to find a concrete answer.

The glacial cirque and valley below the north west side of Yarigatake and formerly glaciated peaks of the Ura Ginza Mountains

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Responses

  1. Peter: many thanks for bringing my attention to your article here – and it’s good to see the vanished glaciers of Japan getting some additional press, in English. You highlight some very interesting issues – why, for example, the Northern Alps of Honshu attracted more glaciation than the (much colder) mountains of Hokkaido.

    And, yes, since you ask – I did read the bit in Ono Yugo’s book about the excavation of the long-lived snowpatch on Tateyama. Alas, though, it turned out not to be a fossil glacier – the nethermost layer was a mere 1,700 years old if I remember rightly.

    But, then again, as your article raises the question, what if glaciers made a brief return in the Little Ice Age … A fascinating question, which I hope someone will one day answer!

    • Well, it was Chris who referred me to your blog, so we can both thank him. I really enjoyed your post. I can get a lot of useful information from your blog and if and when my book gets published, I will be citing your blog or hopefully your book as a reference.

      I didn’t know about the ice near Tateyama being so young but that gets me thinking. I have read that the earth was warmest since the last ice age around five thousand years ago. Presumably there were more global temperature fluctuations between then and the Medieval Warm Period that preceded the Little Ice Age, and if that ice is 1,700 years old then that may point to a cooling trend around that time. If that’s the case, how extensive was the formation of glacial ice in Japan? We could actually ask how long ago did the last real glacier disappear from Japan? Maybe it wasn’t 18,000 to 10,000 years ago but much more recently.

      Yes, Hokkaido is much colder and there seems to be evidence of glaciers having formed in the Hidaka Range. But perhaps Hokkaido’s mountains were simply not high enough. I am not sure about the volcanic history of Daisetsusan, but I read that during the height of the last ice age, Ainodake in the Minami Alps was higher than Fujisan, and that the Yari/Hotaka Range may well have reached 4,000 metres in height (Yama to Keikoku magazine, summer 2008, I think) but the mountains were then eroded by glaciers to near their present elevation.

      Another point about Hokkaido is that I have heard there is no Tsuyu, no rainy season. Though I would imagine that weather patterns were different during the ice age, perhaps if there was a rainy season in Honshu but not Hokkaido then the amount of precipitation in Hokkaido would be less than Honshu and if Honshu’s high mountains received snow instead of rain even during the summer then it might help explain why glaciers formed so readily in the Japan Alps but not in the mountains of Hokkaido.


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