The paper concerns rock avalanches and their deposits reflecting strong interactions with rugged terrain, deformable and wet substrates. Of 186 rockslide-rock avalanche events identified in the Karakoram Himalaya, over 160 show singularities related to run out in rugged terrain. Twelve record complex interactions with substrate materials over large areas of intermontane basins. Other complications arise from travel on to glaciers. 'Complexity' appears in diverse and irregular plan forms recording divergence and splitting of debris streams into multiple lobes. Deposits often have highly asymmetrical long and cross profiles, including Heim's brandling or 'surge' forms against opposing slopes. Morphological complexity is reflected in deposit facies and fabric. Rock avalanches encountering credible and deformable substrate developed extensive longitudinal ('digitate') and transverse ridges. Substrates display complicated folding, faulting and dislocations ('landslide-tectonized' forms). Substrate material penetrate the rock avalanches in multiple dykes, flame, diapir and injection structures. Some debris streams disintegrated to a 'chaos' of substrate and rock avalanche materials. Field diagnostics are emphasised due to a history of misidentification involving, especially, features associated with complex run out. Diagnosis is further complicated by post-emplacement erosion and burial, associated with massive disturbance of Holocene land form development, notably by large rock avalanche dams of which over 90 are identified.
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