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What is deep-seated sliding?

Deep-seated sliding refers to landslides with a relatively deeper sliding surface, lower velocity, less disturbance upon the movement and, in general, an arc sliding surface. Although deep-seated sliding tend to occurs in gentle slopes with a gradient between 5° and 30°, there are also examples of having deep-seated sliding occurred in steep slopes.

A number of unique topographic features often appear upon the occurrence of deep-seated sliding, such as scarp, main body, flank and toe.

(1) Scarp: A horseshoe-shaped scarp slope. The new scarp slop is bright and the crown on the upper edge thereof has a concentric arc-shaped tension crack. Beneath the scarp, there is a depression or ponded water.

 (2) Main body (sliding block): Refers to a wicker scoop-shaped depression with a change in vegetation comparing with surrounding areas. Where the main body is different from surrounding forests for the past many years due to its nature of being a grassland, bamboo woodland or terraced paddy field, its upper surface has a depression; middle surface appears to be a gentle slope; and lower surface forms an uplifted terrain respectively.

(3) Flank (water system characteristics that shows the lateral ditches come from the same source): The lateral sides of the main body are shear fracture zones created by the main body and envelopes. As the soil and rocks thereof are severely damaged and easy-to-be-eroded, two lateral ditches with the same source at the main scarp are gradually formed after a period of time.

(4)Toe: Toe is can damage riverbanks as the displaced landslide materials can narrow or turn the river channel; and form a dammed lake in upstream.