The predominant source of the Sefton Coast beach and dune sand is the bed of the Irish Sea. During the last glacial maximum (Devensian) advancing ice sheets pushed glacial deposits into the Irish Sea basin, and over 10,000 years these have been broken down, sorted and transported by tidal and wind-driven currents.

The prevailing westerly weather and tidal streams both tend to move seabed deposits towards the coast and into the river estuaries, which are both zones of net sediment accumulation. The river Mersey contributes very little sediment to the Sefton Coast; it is mostly intercepted in the Ship Canal. The river Ribble carries fine silt downstream which settles out on the northern Sefton beaches whenever, or wherever, sheltered conditions prevail.

A further source of estuarine accretion (infilling by sediment) is the sand eroded from Formby Point which is moved by tidal and wave-driven currents northwards into the Ribble estuary and southwards into the Mersey estuary.

Formby Point, midway between the Mersey and Ribble estuaries is the meeting zone of the two major estuarine regimes. Tidal streams converge offshore, with the result that a large intertidal sand spit (Taylor's Bank) has developed, aided by the construction in the first half of the 20th century of the river Mersey training walls.