SUMMER 2003GEOHAZARDS COURSE AT UWI, MONA - page 085

Prepared and compiled by Rafi Ahmad, Unit for Disaster Studies,
Department of Geography and Geology,
University of the West Indies, Mona, Kingston 7, Jamaica

BOX NO. 2 LANDSLIDE FUNDAMENTALS


Types of landslide movement
Landslides may occur as falls, topples, lateral spreads, slides, or flows.
Falls are masses dislodged from very steep slopes or escarpments which then free-fall, bounce, or roll downslope. Falls usually move very to extremely rapidly.
Topples are a forward rotation around a pivot point low or below one or more masses.
Lateral spreads are the result of movement involving lateral extension accommodated by shear or tensile fractures. This type of movement is earthquake-induced.
Slides displace masses along one or more discrete planes. Slides may either be rotational or translational in their movement.
Rotational movement is where the plane is curved. The mass rotates backwards around a common point with an axis parallel to the slope. Translational movement is where the plane is more or less planar or gently undulating. The mass moves roughly parallel to the ground surface. More than one form of movement may be represented in some landslides. Movement in this case is often described as complex.

Landslide Materials
1. Landslides may involve displacement of either ROCK, SOIL, or a COMBINATION of the two materials.
2. Rock refers to hard or firm bedrock, which was intact, and in place prior to slope movement.
3. Soil is used in the engineering sense to mean loose, unconsolidated particles or poorly cemented rock or inorganic aggregates. The soil may be residual or transported material.
(NOTE by editor, BLO: soil is specifically NOT transported; if loose material is transported and deposited, it should be referred to as 'sediment")
 4. Soil may be described as either DEBRIS or EARTH. Debris is engineering soil with 20 to 80 percent of the fragments larger than 2mm in size and the remainder smaller. Earth is when 80 percent or more of the soil consists of fragments 2mm or smaller.

BLO 20010531 - - - COMMENTS ? - - - next page - - - Table of Contents