An Earth and environmental sciences concept defining a process, measurement, or principle used to understand Earth and its systems. It applies within stated assumptions and depends on reliable observation and analysis. It does not ensure correct inference without attention to scale, uncertainty, and validation. It supports planning and scientific understanding by linking measurable variables to real-world outcomes. The concept is generally stable, though datasets and analytical tools evolve over time.

Principle

Landslides occur when a pre-existing or newly formed shear surface permits a block or mass to move because driving stresses exceed shear strength along that surface; pore-water pressure, weak layers, and structural discontinuities control the initiation and mode.

Demonstration

A rotational slump in a clay-rich slope where a curved failure surface produces uplifted terraces, or a translational rock slide where a planar bedding plane detaches a rock slab and allows rapid downslope motion.

Misapplication

Labeling any rapid downslope sediment transport (for example, an entrained debris flow or a rockfall of discrete blocks) as a landslide without assessing coherence, failure surface presence, or flow behavior.

Consequence

Landslides can cause abrupt topographic change, destroy infrastructure, block drainage and create temporary dams, and initiate secondary hazards such as flooding or downstream sedimentation.

Reversal

Post-failure re-establishment of slope stability by removal of driving loads, reinforcement of the failure plane, drainage to lower pore pressure, or engineered retaining measures that restore resisting forces.

Boundary

Refers to coherent or semi-coherent failures along a defined surface; excludes flow-dominated phenomena (rapid debris flows, lahars) and pure falls where motion is dominated by free-fall and bounce rather than sliding along a shear plane.

Semantic Tension

Classification conflicts arise at the margins between a slide that disintegrates into a flow, or a slide versus a rockfall when coherence and mode evolve during motion; discipline-specific thresholds for 'slide' versus 'flow' vary.

Synthesis

A landslide is a gravity-driven failure of earth or rock that moves as a mass along a discernible shear surface, characterized by its failure geometry and kinematics and distinguished from flows and falls by coherence and sliding mechanisms.