Definitions of the movement of ground

A grassroots movement is a movement more or less brutal of the soil or sub-soil along a slope. Depending on the speed of movement, there are two types of ground movement : slow (progressive deformation, often imperceptible) and fast. Landslides involve changes to the landscape.

The manifestations of a grassroots movement

Predisposing factors

• The terrain, the slope : a rock falls from the top to the bottom because of its weight, the force of gravity and the slope of the slope. The more slope, the more movements !
• The type of ground : depending on the nature of the soil (rock, earth, sand), the erosion is more or less important. The instability, thus the movement, depends on the type of soil.

Explanatory diagram of the ground motions

Factors precipitating or aggravating

• The weather : heavy rain, wind and drought contribute to the wear of the rock (called erosion). The water seeps into the cracks, the materials move out and become brittle. The soils are less stable.
• The activity of the man : the construction is too large, poorly organized or changing the nature of the soil (excavation, removal of boulders) can aggravate the problem of soil erosion. Furthermore, the deforestation accelerates the process, since the roots of the trees have a stabilizing effect. However, the presence of vegetation material may also play a role as a trigger of falling blocks since the roots may develop cracks, making the unstable blocks.

Source : Booklet teacher-cycle 4 – Project "Pare pa Pare" – French Red Cross – 2024

For more information :

Ground movement – NEMO – Government of Saint Vincent and the Grenadines. Explanations to understand what are the movements of the field, how to deal with it and protect themselves before, during and after. (English)

Movement of ground – Geohazards – French Government. Guide, explanations, practice sheets and French schemes earthquake (French)