ORIGIN OF LAKE-OUTLET DELTAS IN MAINE

Lake-outlet deltas differ from other lacustrine deltas in that they are situated at what is normally the outlet of the lake. Deltas of this type receive sediment only when a flood event in the trunk stream is of sufficient magnitude to cause a flow reversal in the lake's outlet stream. A study of fourteen lake-outlet deltas in Maine indicates that the frequency (once every 2-3 years) and duration (1 to 7 days) of the reversal events are a function of lake size, river flood stage, proximity of the river to the lake, lake drainage area, and cause of the river flooding. The major components of the outlet deltas include well-developed levees, marsh areas, beach ridges, and delta platform. Delta morphology is controlled by the relative importance of riverine versus lacustrine processes. Deltas dominated by river sedimentation are elongate with levees and marshes comprising most of the subaerial delta environment. Where deltaic sediments are strongly reworked by wave action, deltas consist of shore-parallel beach ridges separated by channel fill and marsh deposits. Transitional forms between these two end-members are common.