PARTS OF A LANDSLIDE

OBJECTIVE: Participants will be able to identify different parts of landslides, descriptive terms applied to landslides, and recognize their usefulness in landslide investigation.
CONTENTS:
A. Landslide Nomenclature
1. Because a landslide involves a mass of soil or rock moving downslope, a landslide can be described in terms of differences between the mass forming the landslide and the unfailed slope.
a. The unfailed slope can be termed the original ground surface. This is the slope that existed before the movement took place. If this is the surface of an older landslide, that fact should be noted.
b. The mass that moved is the displaced material. It is the material which moved away from its original position on the slope. It may be in a deformed or undeformed state.
c. The displaced material overlies two distinct zones. The zone of depletion is the area within which the displaced material lies below the original ground surface. The surface of rupture where the mass detached from the slope defines this zone. Where no displaced material remains over the surface of rupture or where flowage rather than rupture occurred, it may be more suitable to call this the source area. The zone of accumulation is the area within which the displaced material lies above the ground surface. This zone is defined by the underlying surface of separation which separates the displaced material from stable material but is not known to have been a surface on which failure occurred. In some instances, it may be more useful to call this zone the depositional area.

2. Parts of a landslide
a. Crown - unfailed area of slope above the landslides. May contain ground cracks called crown cracks.
b. Main scarp - a steep surface on the margin of the slide caused by the movement of displaced material away from the neighboring, unfailed slope. By projecting this scarp under the displaced material, it would become the surface of rupture.
c. Minor scarp - a steep surface on the displaced material produced by differential movement within the displaced material.
d. Toe of surface of rupture - the intersection (sometimes buried) between the lower part of the surface of rupture and the original ground surface. It marks the point separating the zones of accumulation and depletion.
e. Head - the upper part of the displaced material along the contact between the material and the main scarp.
f. Top - the highest point of contact between the displaced material and the main scarp.
g. Main body - the part of the displaced material that overlies the surface of rupture between the main scarp and the the toe of the surface or rupture.
h. Flank - the side of the landslide.
i. Foot - that portion of the displaced material that lies downslope from the toe of the surface of rupture.
j. Toe - the margin of displaced material most distant from the main scarp.
k. Tip - the point on the toe most distant from the top of the slide.

l. NOTE: Not all parts of a landslide may be present due to past movement deformation or the nature of the slope movement.