MORPHO-SEDIMENTARY DEVELOPMENT OF DRUMLIN-FLANK BARRIERS WITH RAPIDLY RISING SEA-LEVEL, STORY HEAD, NOVA-SCOTIA

The morphodynamic and morphosedimentary development of drift-aligned and swash-aligned coarse barriers plays an important role in the evolution of paraglacial coasts. This paper discusses the development of two contrasting barriers attached to a drumlin headland at Story Head on the Atlantic coast of Nova Scotia, southeastern Canada. A 3-4 mm a-1 sea-level rise is forcing rapid barrier changes, including landward migration (rollover) or the swash-aligned barrier at 5-8 m a-1, and barrier thinning, elongation and breaching. Morphological development reflects the highly variable longshore distribution of wave power, imposed initially by the topography of the drumlin and its position in the incident wave field, and later by morphosedimentary feedback resulting from such gradients. Gradual reduction of an inherently intermittent sediment supply leads to reworking (cannibalization) of the barrier, ultimately finding expression in a series of distinct wave-formed sediment cells. Further diminution of the sediment supply, coupled to cell development, results in the drift-aligned system decaying into a series of high-water residuals, separated by breach depressions, with splayed spit recurves at the margins. Although the swash-aligned barrier is stretched within the predominant overwash regime and may eventually separate from the headland, it has remained intact until very recently, when an initial breach occurred. The evolutionary sequence of the headland-barrier system has an important effect on adjacent sedimentary environments.