Landslides associated with recent road constructions in the Río Lucma catchment, eastern Cordillera Blanca, Peru.

Extensive road construction works recently took place in the remote eastern part of the Peruvian Cordillera Blanca, aiming at a better connection of isolated mountain communities with regional administrative centres. Here we document and characterize landslides associated with these road construction efforts in the Río Lucma catchment, Peru. We show that a total area of 321,332 m2 has been affected by landslides along the 47.1 km of roads constructed between 2015 and 2018. While landslides downslope the roads (48.2%) and complex landslides crossing the roads (46.4%) were the most frequent landslide types in relation to the position of the road; slide-type movement (60.7%) prevails over the flow-type movement (39.3%). Timewise, we found that 75.0% of landslides were observed simultaneously with road construction work, while the remaining 25.0% occurred up to seven months after the roads had been constructed. We plotted the lagged occurrence of these subsequent landslides against precipitation data, showing that 85.7% of them were observed during the wet season (November to April). We conclude that the majority of mapped landslides were directly associated with road constructions and that the road constructions also may set preconditions for landslides, which mainly occurred during the subsequent wet season.

Detecting landslide-dammed lakes on Sentinel-2 imagery and monitoring their spatio-temporal evolution following the Kaikoura earthquake in New Zealand.

Landslide-dammed lakes pose a risk for upriver and downriver communities and infrastructure. The 2016 Kaikoura earthquake affected the northeastern region of the South Island in New Zealand, triggering numerous landslides that dammed river courses leading to the formation of hundreds of dammed lakes. Detecting and monitoring landslide-dammed lakes is important for disaster management. Satellite remote sensing imagery is often complementary to field acquisitions to obtain an overview of large and remote areas and thus can be exploited to monitor landslide-dammed lakes. Yet, the strengths and limitations of freely available multi-temporal satellite imagery for landslide-dammed lake assessment remain largely unexplored. This study aimed at automatically mapping landslide-dammed lakes caused by the 2016 Kaikoura earthquake and monitoring their evolution using time series of Sentinel-2 imagery and the computing capabilities of the Google Earth Engine. Our approach combined dynamic thresholding, change detection, and connected component analysis. Landslide-dammed lakes larger than 300 m2 and located on relatively flat terrain were detected with reasonable accuracy, while lakes located in steeply incised valleys were detected less frequently. Despite the challenging topographical and environmental characteristics of the study area, we were able to detect landslide-dammed lake candidates at a regional scale. Temporal monitoring of the evolution of the landslide-dammed lake area revealed four distinct patterns: 1) constant, 2) increasing, 3) decreasing, and 4) variable. Our approach contributes to the understanding of the utility and limitations of temporal and spatial monitoring of landslide-dammed lakes, their potential cascading hazards and their interactions.

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

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.