Elaboration of a magnitude-frequency relationship for debris flows by aerial photographs: case study from a national park in the Spanish Pyrenees

Abstract

Magnitude—frequency relationships provide essential information for landslide hazard and risk analysis. A debris-flow inventory was created in the “Aigüestortes i Estany de Sant Maurici” National Park in the Central Pyrenees, Spain, by the interpretation of several sets of aerial photographs covering a time span of 53 years. 194 debris flows were detected, which provide a spatial density of 0.5 events per square kilometre. The areas affected by the debris flows range from ∼200 m2 up to 35000 m2. The magnitude—cumulative frequency curves include a strong rollover effect at about 2000 m2 and events larger than this magnitude can be represented by a power law with an exponent between −1.5 and −1.9.