Landslides in the Cordillera Blanca

Landslides are essential for the landscape character in Cordillera Blanca Mts. where they also represent natural hazard with potentially catastrophic effects on society. This is why the traditional knowledge of the mountain inhabitants contains explanations of their origin as well as measures mitigating their negative impacts and this information proved to be useful for scientific research and in landslide risk reduction efforts. Landslide spatial and temporal distribution as well as scientific knowledge about them is uneven. Most of the documented landslides of different types were mapped in Mesozoic sediments and metamorphic rocks, while granites are less susceptible with rock falls as the prevailing landslide type. Cordillera Blanca landslides are triggered by earthquakes capable of initiating thousands of landslides ranging from single boulder falls to extremely voluminous and fast ice/rock avalanches, which claimed about 6000 casualties during the May 31st 1970 earthquake. Prolonged and intensive precipitations during the annual rainy seasons along with glacier melt water are responsible for increased groundwater levels triggering rock or debris slides and flows. The number of reported landslides whose origin is linked to permafrost degradation is still rather small, but their future frequency is expected to significantly increase due to observed and predicted global warming. They often impact recently enlarging and newly forming glacial lakes and initiate chains of hazardous processes. They possibly result in far-reaching floods which attract a lot of scientific attention. If future research is to gather the necessary information to effectively reduce landslide risk, it must focus on previously neglected (e.g., landslides and debris flows in the piedmont region) or under-researched (e.g., mountain permafrost conditions) topics searching for ways to include traditional knowledge in the investigations and results application.