Cliff collapse - Rock fall

Japanese: 崖崩れ - がけくずれ
Cliff collapse - Rock fall

A phenomenon in which a steep natural slope suddenly slides down due to heavy rain or an earthquake. Most cliff collapses are seen on terrace cliffs such as coastal and river terraces, and are generally shallow surface collapses. Cliff collapses can occur in any type of geology, but areas with weathered granite and areas with volcanic eruptions are at high risk of cliff collapses. The water that causes cliff collapses is an intermediate flow that flows near the surface, and is most affected by heavy rainfall over a relatively short period of time. Although the number of cliff collapses is small, some cliff collapses occur in response to a total amount of rainfall over a long period of time. The impact of human activity around cliffs on cliff collapses should also not be overlooked. For example, if there is farmland or housing complexes on the plateau at the top of the cliff, care should be taken as poor wastewater treatment there can cause cliff collapses. Under the Law Concerning the Prevention of Disasters Caused by Collapse of Steep Slopes (1969), countermeasures are being implemented for natural slopes with an inclination angle of 30 degrees or more, a vertical height of 5 meters or more, and which could cause significant damage to five or more houses or public buildings.

[Kazuo Ashida and Takahisa Mizuyama]

[References] | Coastal terraces | River terraces | Shirasu | Terraces | Landslides

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

急勾配(こうばい)の自然斜面が豪雨や地震などの作用により突発的に滑落する現象。崖崩れの多くは海岸段丘や河岸段丘のような段丘崖(がい)にみられ、一般に浅い表層崩壊である。どのような地質でもおこりうるが、花崗(かこう)岩の風化したマサ土地帯や火山噴出物のシラス地帯は崖崩れの危険度が高い。崖崩れを引き起こす水は表層近くを流れる中間流で、比較的短時間の強雨がもっとも影響する。数は少ないが、長時間の総雨量に対応して発生する崖崩れもある。崖周辺における人間の活動が崖崩れに及ぼす影響も見逃せない。たとえば、崖上部の台地に農地や住宅団地がある場合など、そこでの排水処理のまずさが崖崩れの原因となることもあるので注意が必要である。「急傾斜地の崩壊による災害の防止に関する法律」(1969)によって、傾斜角が30度以上の自然斜面で、斜面の直高が5メートル以上、かつ人家5戸以上または公共建物に著しい被害を及ぼすものを対象として対策事業が進められている。

[芦田和男・水山高久]

[参照項目] | 海岸段丘 | 河岸段丘 | シラス | 段丘 | 山崩れ

出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例

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