Distinct mechanisms of landslides in moraines associated with the post-LIA glacier thinning: observations from the Kinzl glacier, Huascarán, Peru

The Kinzl glacier (N Huascarán, Cordillera Blanca, Peru) is surrounded by welldeveloped Little Ice Age (LIA) moraines. Here we interpret distinct mechanisms of landslides in these moraines and link them to glacier retreat and thinning, based on the field observations and analysis of old field (since 1932) and remotely-sensed (since 1948) images. Three types of landslides are distinguished according to the cross-profile morphology: (i) type „N“; (ii) type „M“; and (iii) type „A“ (see Fig. 1). The occurrence of all these types is associated with glacial ice loss and downwasting occurring since the end of the LIA and might represent a trigger of glacial lake outburst floods (GLOFs) if a lake is developed. We show that sliding of type „N“ is likely gradual process which takes place simultaneously to glacier downwasting (speed < 1m/yr); in contrast, type „A“ can occur rather rapidly at any time once glacier has downwasted and does not anymore support nearly vertical inner slopes of lateral moraines. Despite generally poorly sorted moraine material, landslides of types „N“ and „M“ are internally integrated, keeping its shape during the sliding (hundred meters long, unbroken blocks moving), while type „A“ is internally disintegrated. Investigated landslides are characterised by movement perpendicular to the direction of the flow of the glacier, and width > length. In the regional context, landslides in the LIA moraines of the Kinzl glacier are unique considering their volume up to 1 Mm3.