Debris Flow Dating and Magnitude Reconstruction

Abstract

Debris flows typically occur in mountain regions with high energy relief, complex geology and extreme climate conditions, where they often affect humans as well as their cultural and economic assets. Understanding the frequency and magnitude of debris flows is essential to conduct reliable hazard and risk assessments in the context of climate warming. However, observational records of past and recent debris flows are unusual worldwide and difficult to gather. In this chapter, we review methodological advances (after Jakob, Debris flow hazards and related phenomena, Springer, 2005) on debris flow dating and magnitude estimation. We briefly describe the theoretical basis of classical absolute and relative dating techniques, including radiometric, botanical and historical as well as modern approaches based on remote sensing. We also review different existing strategies to quantify the magnitude of debris flow retrospectively, including empirical equations on different parameters (volume, affected area, peak discharge or frontal flow velocity) and the use of latest-available numerical models. Finally, we discuss the applicability and limitations of the frequency-magnitude relationship in the context of hazard and risk assessments. The approaches provided in this chapter are grounded on field-truthed evidence and contribute to more assertive spatial decision-making and to build more resilient societies in the context of climate warming.