Banded sulfur sediments, characterized by alternate layers of yellowish, fine-grained sulfur and dark gray clays, occur in a now-extinct crater lake of the Tateyama volcano, central Japan. Stratigraphic variations in the sulfur content, sulfur isotopic ratio, mineralogy, and content of diatom fossils suggest that the lamination represents seasonal repetition of environmental conditions of the lake water; colloidal sulfur, formed by oxidation of volcanic H2S in the presence of dissolved oxygen, and freshwater benthonic diatoms <Pinnularia braunii (Grun.) Cl, var. amphicephala (A. Mayer) Hust.>, flourished during oxidative-convective periods, whereas detrital materials rich in clays were deposited onto the lake bottom during reducing-stagnant periods. a sedimentation period of 3000 to 4000 years is calculated from the total thickness of the banded sulfur sediments coupled with the sedimentation rates of 1 to 2 mm/yr deduced from the above model. The estimated period is in good agreement with the age for phreatic explosion (3000 to 6300 year ago based on tephra chronology), which created the crater lake.