Recent warming has had enormous impacts on glaciers and high-mountain environments. Hazards have changed or new ones have emerged, including those from glacier lakes that form as glaciers retreat. The Andes of Peru have repeatedly been severely impacted by glacier lake outburst floods in the past. An important recent event occurred in the Cordillera Blanca in 2010 when an ice avalanche impacted a glacier lake and triggered an outburst flood that affected the downstream communities and city of Carhuaz. In this study we evaluate how such complex cascades of mass movement processes can be simulated coupling different physically-based numerical models. We furthermore develop an approach that allows us to elaborate corresponding hazard maps according to existing guidelines for debris flows and based on modelling results and field work.

This experimental study provides a characterization of the flow field created by bed discordance at a fixed 70 ${}^{\circ }$ open-channel confluence on the basis of detailed free surface topography and three-component acoustic Doppler velocimetry measurements, which are contrasted with the results for a concordant bed junction. Due to bed discordance, the jet-like flow from the tributary is bent downstream to be aligned with the main channel axis. Underneath the tributary backward-facing step, separation occurs, producing negative vorticity along the main channel axis. A strong secondary motion downstream of the tributary junction is related to flow separation at the step and to flow release from the jet-like flow induced by a difference in the curvature of jet-like motion. A quantification of the terms in the equation of conservation of the longitudinal vorticity shows that the vortex stretching terms are sufficient to explain the development of the helical motion, which is thus classified as a secondary motion of Prandtl's first kind.