Natural Risks in Mountains: Rock Movements from Triggering to Protection

Flashcards covering key vocabulary related to natural risks in mountains, focusing on rock movements, their causes, different types, associated risks, and protection methods, based on the provided lecture notes.

Photogramétrie

The use of photographs to understand the history of rock destabilizations.

Forêt de protection

A forest used as a method of managing risks associated with rock movements, often acting as a barrier.

Lave torrentielle

A debris flow characterized by very coarse debris downstream and smaller blocks upstream.

Permafrost

A thermal state where lithospheric material remains non-visible but its presence is evidenced by phenomena like rock glaciers. It is typically found above an altitude of 2500m in the French Alps.

Processus en cascade

A chain of events where one geological event, such as a rock detachment, triggers subsequent events like glacier destruction and mudflows.

Chute de pierres/blocs

A rock movement involving volumes less than 10m³, traveling at several tens of km/h.

Éboulement

A rock movement involving volumes between 10m³ and 100m³, traveling at several tens of km/h.

Écroulement

A rock movement involving volumes greater than 100m³, occurring at high altitude and traveling at several tens of km/h.

Avalanche rocheuse

A very large rock movement involving volumes greater than 100,000m³, which can reach speeds of up to 180km/h.

Mouvements versants

A general term for slope movements, which can include phases of rolling, sliding, bouncing, and flying.

Rupture (géologie)

The process where a rock mass completely detaches from its starting zone, leaving a scar on the rock face.

Zone de dépôt

The area where dislodged rock blocks eventually come to a stop.

Rhéologie

The study of how matter evolves under stress, encompassing elastic, plastic, and rupture deformations.

Cryoclastie/Hydroclastie

Mechanical alteration where ice forms in rock fissures, expanding by 9% and causing the rock to break.

Haloclastie

Mechanical alteration caused by the recrystallization of minerals brought by water, leading to rock fragmentation.

Bio-météorisation

The alteration of rock by the action of living organisms, fragmenting it into smaller elements without changing its chemical composition.

Décompression post-glaciaire (Paraglaciaire)

Non-glacial processes that condition the evolution of slopes, often involving fracturing due to pressure release after glacier retreat.

Karstification

A chemical alteration process involving the dissolution of limestone by carbonic acid, leading to the formation of specific landforms.

Glissement de plan

A type of rock movement where the rock mass slides along a single plane of discontinuity.

Glissement dièdre

A type of rock movement where the rock mass slides along two intersecting planes of discontinuity.

Rupture de surplomb

A type of rock movement characterized by the failure and detachment of an overhanging rock mass.

Basculement de colonne ou de bloc

A type of rock movement where a column or block topples over due to instability.

Risque (géologie)

The intersection between a natural phenomenon and vulnerability. It is represented by the formula: Exposure to hazard * Vulnerability.

Effets de cascades

Indirect risks resulting from a chain reaction, where one event triggers several others.

PPR (Plan de Prévention des Risques)

A regulatory document under French law serving as a public utility easement, outlining risk zones and defining measures to reduce potential risks.

Protection passive

Risk management measures that create a physical screen or barrier between the natural hazard and the vulnerability of assets or people, such as nets, galleries, or earth mounds.

Casquette avec plots fusibles

A protection structure for infrastructure, where a canopy is equipped with sacrificial (fusible) elements that are cheaper to repair or replace than the entire structure after an impact.

Protection active

Risk management actions that directly oppose the manifestation of geological phenomena, such as rock bolting (clouage) or cabling to stabilize rock masses.

Clouage

A protection technique involving the installation of steel anchors (nails) into drilled holes, traversing unstable rock mass and extending into stable rock for reinforcement.

Béton projeté

A layer of quick-setting concrete sprayed onto rock surfaces, primarily used to stabilize rock masses with superficial degradation and prevent small block falls.

Purges de parois

Temporary protection measures involving the removal of unstable rock sections, either manually or through controlled blasting.

DGPV (Déformation Gravitaire Profonde de Versant)

Deep-seated gravitational slope deformation, a type of large-scale slope instability that is often difficult to treat, requiring extensive monitoring.

Trajectographie

The modeling and study of the potential paths and trajectories of moving rock blocks on a slope.

Bloc clé

A specific block within a rock mass whose removal leads to the destabilization and potential collapse of a larger assemblage of blocks.