Eruption of liquid H2O magmas along extensional fractures and graben-bounding normal faults may have played a critical role in the development of Ganymede's grooved terrain. The resurfacing potential of a water magma is dependent on a variety of factors, including the areal extent of the source region, the rate of discharge, the thickness of the flow, and the time that it takes the flow to completely freeze to its base. In this paper the thermal evolution of such a flow is considered in detail. The minimum unfrozen lifetime of a 5-m flow is approximately 12.5 days while a 10-m flow would survive for at least 50 days. Heating resulting from frictional head loss could reasonably extend these lifetimes by 50% or more. With a discharge rate of the order of 1--10 km3 d-1, an individual volcanic water flow could flood an area of ~104 km2 before freezing. As the flow solidifies, its volume will increase, thus lifting and arching its protective ice cover. Extensional fractures may then develop in the ice subparallel to the graben walls. These fractures could result in grooves directly, given a sufficiently thick (~1 km) flow, or they may simply act to concentrate various tectonic forces that could initiate groove-producing faults. ¿ American Geophysical Union 1987