We performed flume experiments to examine tsunami flow conditions, sedimentary processes, and the distribution of tsunami deposits on a narrow coastal lowland backed by a cliff. The experiments directed tsunamis of eight magnitudes onto a terrestrial model of a narrow coastal plain backed by a cliff, and the results were compared with those of similar, previously conducted experiments without a cliff. In the experimental series with the cliff, the tsunami flow was blocked and pooled, and, as a consequence, the flow changed from supercritical to subcritical with a hydraulic jump. The flow transformation forced the suspended sediment in the subsequent flow to stall and deposit. As a result, the distribution of deposits show a local maximum at a short distance from the cliff, in particular in the case of larger tsunami flows. This result suggests that an impeder such as a cliff can cause transformation of a tsunami flow and locally thick deposits.