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Description

The SPIRAL inventory data model was designed to consistently record slope movements across the Pyrenean region. Three requirements were established, 1) to facilitate data entry, 2) to highlight essential characteristics for risk management (including consequences), and 3) to maintain academic rigor in classification. The objective is to provide a practical tool for technicians, administrations, and specialists to analyse the spatial and temporal distribution of phenomena and assess their impact.

For the classification of phenomena, a dual strategy was established: an initial simplified classification based on the most common geological processes generating ground deformation in the mountain range, and a second “complete” classification based on the Varnes classification (Hungr et al., 2014).

The simplified classification consists of 4 categories that are briefly explained in the following sections:

Rockfalls

Imatge

Slope movements occurring on steep slopes along a surface where the mobilized mass undergoes mainly aerial movement, with limited contact with the ground surface, typically experiencing fragmentation or disintegration during its trajectory. 

On cliffs, movement generally occurs by free fall, which upon impacting gentler slopes continues by bouncing and eventually rolling.

These are very rapid, spontaneous, and sudden movements with high mobility, as their propagation paths usually extend much farther than the initial failure point.

Landslides

Imatge

Movement of a mass of soil or rock along a sliding surface, where intense shear deformation controls the movement. The rupture surface may take various forms, most commonly circular or planar, leading to rotational, translational, and/or complex movements. 

In general, landslides involve the movement of a mass in continuous contact with the underlying ground, and the displaced material largely retains its original internal structure. Deformation is concentrated along rupture surfaces.

The mobility of landslides varies greatly depending on their nature and size relative to the slope, but typically a large portion of the displaced mass remains near the initial rupture area. Their velocity is also highly variable, ranging from very rapid, sudden events to slow and progressive movements.

Debris flows (torrential flows)

Imatge

Ground movements in which the mass becomes fluidized, losing its original internal structure and acquiring a viscous behaviour that enables it to travel beyond the initiation area. Flows consist of mixtures of solid particles and water in widely varying proportions and compositions. 

Particle size varies, and together with the solid/liquid ratio, determines the flow’s dynamic behaviour (Pierson and Costa, 1987).

Debris flows are very rapid and highly mobile, often traveling far beyond their origin.

Deep-seated slope deformations

Imatge

Movements affecting an entire slope or a large portion of it. They may or may not have a clearly defined rupture surface, which is typically deep in the central part of the movement. The nature of the mobilized material depends on the slope typologies but generally includes both surface soil and underlying bedrock, often involving multiple material types described by Cruden and Varnes (1996). 

The displaced mass largely loses its internal structure, although large blocks may still preserve it.

This category includes phenomena such as rockslides, debris avalanches, rock avalanches, lateral spreads, and deep-seated gravitational slope deformations (DSGSD).

Data source of the SPIRAL inventory: AR+I, Andorra Research and Innovation; BRGM, Office of Geological and Mining Research (France); ICGC; IGME, Geological and Mining Institute of Spain; UNIZAR, University of Zaragoza; UPV, University of the Basque Country.

References

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