Banded Pumice Block of banded andesite-dacite pumice erupted on May 22, 1915. This initially large block of hot pumice fell on the eastern slopes of Lassen Peak and broke along a set of polyhedral joints that formed as it cooled in place. The striking color banding reflects mingling of two compositional varieties of erupted magma, contorted by flowage of the incompletely mixed viscous liquids. Photo by R. L. Christiansen, September, 1987.