typically given more specific names. These include: Lahar A lahar is a debris flow related in some way to volcanic activity, either directly as a result of an eruption, or indirectly by the collapse of loose material on the flanks of a volcano. A variety of phenomena may trigger a lahar, including melting of glacial ice, intense rainfall on loose pyroclastic material, or the outburst of a lake that was previously dammed by pyroclastic or glacial sediments. The word lahar is of Indonesian origin, but is now routinely used by geologists worldwide to describe volcanogenic debris flows. Nearly all of Earth's largest, most destructive debris flows are lahars that originate on volcanoes. An example is the lahar that inundated the city of Armero, Colombia. Jökulhlaup A jökulhlaup is a glacial outburst flood. Jökulhlaup is an Icelandic word, and in Iceland many glacial outburst floods are triggered by sub-glacial volcanic eruptions. (Iceland sits atop the Mid-Atlantic Ridge, which is formed by a chain of mostly submarine volcanoes). Elsewhere, a more common cause of jökulhlaups is the breaching of ice-dammed or moraine-dammed lakes. Such breaching events are often caused by the sudden calving of glacier ice into a lake, which then causes a displacement wave to breach a moraine or ice dam. Downvalley of the breach point, a jökulhlaup may increase greatly in size through entrainment of loose sediment from the valley through which it travels. Ample entrainment can enable the flood to transform to a debris flow. Travel distances may exceed 100 km. Theories and models of debris flows Numerous different approaches have been used to model debris-flow properties, kinematics, and dynamics. Some are listed here. Rheologically based models that apply to mud flows treat debris flows as single-phase homogeneous materials (Examples include: Bingham, viscoplastic, Bagnold-type dilatant fluid, thixotropic, etc.) Dam break wave, e.g. Hunt, Chanson et al. Roll wave, e.g., Takahashi, Davies Progressive wave A type of translating rock dam Calibrating and validating such sophisticated models require well-documented data from field surveys or minute laboratory experiments. Two-phase The mixture theory, originally proposed by Iverson and later adopted and modified by others, treats debris flows as two-phase solid-fluid mixtures. In real two-phase (debris) mass flows there exists a strong coupling between the solid and the fluid momentum transfer, where the solid's normal stress is reduced by buoyancy, which in turn diminishes the frictional resistance, enhances the pressure gradient, and reduces the