Distinct types of landslides in moraines associated with the post-LIA glacier thinning: Observations from the Kinzl Glacier, Huascarán, Peru

Abstract

The Kinzl Glacier is a unique dendritic-type glacier of the Peruvian Cordillera Blanca and is surrounded by well-developed Little Ice Age (LIA) moraines. Based on field observations and analysis of historical photographs (since 1932) and remotely sensed images (since 1948), we interpret distinct mechanisms of landslides in these moraines and link them to glacier retreat and thinning. Three types of landslides are distinguished according to the cross-profile morphology: (i) type “N”, (ii) type “M” and (iii) type “A”. Our data show that sliding of type “N” is an ice-contact slope failure that occurs as a gradual process simultaneously to glacier downwasting. In contrast, type “A” can occur at any time once the glacier has downwasted below the sliding plane and cannot buttress the nearly vertical inner slopes of the moraine anymore. We further argue that the type “M” can gradually evolve from type “N” or can occur as an episodic event. Probably due to overconsolidation of moraine material, landslides of types “N” and “M” keep their shape during sliding and move in form of several hundred meters long unbroken blocks. In contrast type “A” is internally disintegrated during landsilding. All investigated landslide types are characterized by increased width-length ratio and movement perpendicular to the direction of the flow of the glacier. We opine that the occurrence of these landslide types is directly or indirectly associated with glacial ice loss occurring since the end of the LIA. The observed landslides in the LIA moraines of the Kinzl Glacier are unique in the regional context considering their estimated size on the order of 106 m3 and contribute significantly to the paraglacial adjustment of moraine slopes and landform evolution in the post-LIA context. Apart from their role in moraine evolution, these landslides can trigger hazardous cascading process-chains in high-alpine environments.