ABSTRACTThe formation of a large boulder delta complex found in the Båldakatj area, Swedish Lapland, is related to the catastrophic drainage of ice-dammed lakes. The interpretation of the sedimentological characteristics of these boulder deposits has resulted in the recognition of at least two phases in their development. An initial deposition of material by debris flows was subsequently followed by erosion and deposition by fluvial processes. The resulting reworking of the material was not uniform throughout the area. Two major lobes of boulder deposits can be recognized. These lobes have been exposed to different processes, as interpreted by differences in morphological and sedimentological characteristics, such as gradient, distal slope, channel pattern, scour marks, and the size, shape, roundness, imbrication and sorting of particles. Scour marks around large boulders occur frequently in the study area. They proved to be excellent flow direction indicators. The literature on similar boulder deposits, formed by flood flows or debris flows, in other regions or environments, has been reviewed and the results compiled for comparative purposes.