Evolution of the covered glaciers in the Cordillera Blanca during the period 1962 - 2020

Glacier dynamics and the effects of climate change accelerate bedrock erosion and instability of the surrounding topography, causing clean glaciers to be gradually covered by debris, particularly in the ablation zones. While the area of glaciers covered worldwide is increasing, there are few studies on this phenomenon in tropical glaciers and its possible significant effects on glacier melt. In this context, this study analyzes the spatio-temporal evolution of the area of glaciers covered by debris in the Cordillera Blanca from 1962 to 2020. 

To achieve this aim, we used data from the Peruvian National Glacier Inventory for 1962 and 2020. We also identify the covered glaciers through the photo-interpretation of geomorphological features, such as the color and texture of the ground surface, the presence of thermokarst zones, and the formation of small lakes/lagoons observed in the satellite images. In addition, we got the topographic features from the ALOS PALSAR digital elevation model.

The outcomes of this investigation reveal an increase in the number and surface area of glaciers covered, from 33 units (15.41 km2) in 1962 to 173 units (23.06 km2) in 2020. This shows an increase of 49.64% from the glacier area covered by debris. The increase in covered glaciers in the Cordillera Blanca could be because many glaciers identified as debris-free in 1962 were partially or totally covered in 2020; 17.13 km2 of the glacier debris-free area was covered by debris during this period. It has been observed that 93% of the area covered by debris is on slopes greater than 8°. Of these, 25% were in the 24° - 33° range, and 23% were on steeper slopes than 33°. The orientation analysis indicates a predominance of surface covered towards the southwest and south.

Likewise, the areas of glacier retreat covered between 1962 and 2020 were analyzed, identifying 9.45 km2 of glacier surface loss. 18% of the loss areas are on slopes steeper than 8º, mainly from 8º to 17º slope, where 28% of the loss area is located. Meanwhile, a clear retreat trend is observed in those areas with a north orientation of 95% and a northeast orientation of 5%.

These findings suggest a possible association between the higher magnitude slope conditions and the formation of covered glaciers, while the orientation influences the retreat of these glaciers.