Flood release structures of high-head dams generate high-velocity plunging jets. These may scour the downstream rocky riverbed and even damage the dam foundation. Assessment of the scour evolution is essential to ensure the safety of the dam and appurtenant structures, as well as to guarantee the stability of its abutments.In the framework of a research project, near-prototype scaled experimental installation generating high-velocity jet impact in a plunge pool has been equipped with an artificial rock block. Pressure fluctuations over and under the block as well corresponding block movements are recorded for a jet impacting at the block upper face. The jet impact is situated along one of the block side faces, resulting in asymmetrical jet impact conditions. The analysis focuses on the reponse of the block due to the water pressures acting above the block and inside the fissures surrounding for both core and developed jets.