Reconstruction of the 1941 GLOF process chain at Lake Palcaco- 1 cha (Cordillera Blanca, Perú) 2

The Cordillera Blanca in Perú has been the scene of rapid deglaciation for many decades. One of numer- 20 ous lakes formed in the front of the retreating glaciers is the moraine-dammed Lake Palcacocha, which 21 drained suddenly due to an unknown cause in 1941. The resulting Glacial Lake Outburst Flood (GLOF) 22 led to dam failure and complete drainage of Lake Jircacocha downstream, and to major destruction and 23 thousands of fatalities in the city of Huaráz at a distance of 23 km. We chose an integrated approach to 24 revisit the 1941 event in terms of topographic reconstruction and numerical back-calculation with the 25 GIS-based open source mass flow/process chain simulation of the moraine dam. However, the involvement of Lake Jircacocha disguises part of the signal of process 36 initiation farther downstream. Predictive simulations of possible future events have to be based on a 37 larger set of back-calculated GLOF process chains, taking into account the expected parameter uncer- 38 tainties and appropriate strategies to deal with critical threshold effects.