The Sakae village landslide in Japan

In the morning of 9 May 2022 a significant landslide occurred near to Sakae Village in northern part of Nagano Prefecture in Japan.  Saito Hitoshi (@GinHS) from Nagoya University has tweeted about this landslide, noting that it has partially blocked the valley:-

長野県栄村の斜面崩壊。推定崩壊土砂量は約140,000 m3、小規模な天然ダムもできているように見える。湯沢砂防事務所： https://t.co/6YQVizHKKD pic.twitter.com/LifLH8KOKS

— 齋藤　仁／Saito Hitoshi (@GinHS) May 10, 2022

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A rough translation of the tweet is: “The slope collapse of Sakae Village, Nagano Prefecture. The estimated amount of collapsed sediment is about 140,000 cubic metres, and it seems that a small natural dam has also been created.”

In a further tweet he has pinpointed the location:-

対岸は尾根筋だしヤバそうですね。ここ閉塞すると切明もまずいのか。しかし地すべりだらけですね。https://t.co/ZietfIqEXv pic.twitter.com/lqDjLGvroP

— ちずらぼ (@chizulabo) May 10, 2022

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The link provides further detail of the site, which is centred on 36.813, 138.623.  The Google Earth image shows a small existing failure at this location.  The map above highlights that the Sakae Village landslide has occurred in terrain that has many existing failures, and that the topography of the site indicates that this is likely to be a reactivation.  The location on the outside of a bend in the river suggests that erosion of the toe is likely to have been a factor in the triggering of the most recent failure.

NHK has an article in Japanese that provides greater detail about the landslide.  It is about 100 m long, 200 m wide and about 7 m deep.  The estimated volume is, as noted above, 140,000 cubic metres.

The best image that I have been able to obtain is in a pdf document released by the Ministry of Land, Infrastructure, Transport and Tourism of Hokuriku Regional Development Bureau:-

The 9 May 2022 landslide at Sakae Village in Japan. Image from the Ministry of Land, Infrastructure, Transport and Tourism of Hokuriku Regional Development Bureau.

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The video in the NHK article and the image above both indicate that there is water flow past the dam, indicating that the risk associated with valley blockage from the Sakae Village landslide is small.

Japan is probably the most capable country in dealing with landslides, based upon many decades of experience.