hillside phenomena or hillside movements are movements of masses of land or rocks that are on a slope "Slope (geography)"). They are due to the instability of the materials that make up the slope. These displacements occur in the direction of the slope as a consequence of the force of gravity.

Different hillside phenomena can be differentiated according to the type of movement by which the materials move:

Various factors influence slope movements.

The main factors referring to the structure of the slope are gravity, the inclination of the slope "Slope (geography)"), the arrangement of the strata parallel to the slope and the alternation of strata with different permeability.

There are also external factors such as the climate of the area, the use of the land by humans and the absence of vegetation, since the vegetation absorbs rainwater, prevents runoff and favors the support of the land.

In addition, there are triggering factors for hillside phenomena such as water, earthquakes, erosive processes and anthropogenic actions.

Hillside movements pose a geological risk for the population and their property. To reduce the chances of this risk materializing, it is necessary to carry out a series of preventive measures.

These measures are mainly based on the use of engineering structures as protection. There are two classes: