Genesis and implication of soft-sediment deformation structures in high-energy fluvial deposits of the Alaknanda Valley, Garhwal Himalaya, India

• SSDS were identified in the high-energy fluvial environment.
• Most of the SSDS are aseismically formed in Alaknanda Valley.
• SSDS were mainly formed by flood surges.
• Ground fissures were formed by earthquake.

Valley-fill terraces and fluvio-lacustrine sediment successions were investigated for the nature and type of soft-sediment deformation structures (SSDS) in the Alaknanda Valley of the Garhwal Himalaya. Based on their morphologies, sediment characteristics and comparison with existing data on SSDS, these features are classified into seismic and aseismic categories. The study indicates that, despite the terrain being in the seismically active domain of the Central Himalaya, the majority of the deformation structures seem to have been generated aseismically. We attribute their genesis to uneven loading, slope failure and, most importantly, turbulent flow and sudden loading by flash floods. The study suggests that a cautious approach is needed before assigning a seismic origin to deformation structures in sediments deposited in high-energy fluvial systems.