AbstractA protalus rampart is being actively formed on the perennial snow patch in the Kuranosuke Cirque, Northern Japanese Alps. This paper describes its form, constituting materials, and the processes actually operating on it. The field observations of three years reveal that alpine debris flows play a more important role in the present construction of the protalus rampart than rock falls. The conditions under which alpine debris flows occur were estimated in relation to surface materials, areal snow-melt pattern, and precipitation data. Generally alpine debris flows on the order of 101–102m3occur in the Kuranosuke Cirque. The return periods of debris flows on the order of 102m3are estimated to be 4 years. On the basis of these data, debris flows on the order of 103m3and a landslide are hypothesized for an origin of the protalus rampart of the Kuranosuke Cirque.