Raised beach

A raised beach, marine terrace, coastal terrace, or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin, mostly an old abrasion platform which has been lifted out of the sphere of wave activity (sometimes called "tread"). Thus, it lies above or under the current sea level, depending on the time of its formation. It is bounded by a steeper ascending slope on the landward side and a steeper descending slope on the seaward side (sometimes called "riser"). Due to its generally flat shape it is often used for anthropogenic structures such as settlements and infrastructure.

A raised beach is an emergent coastal landform. Raised beaches and marine terraces are beaches or wave-cut platforms raised above the shoreline by a relative fall in the sea level.

Around the world, a combination of tectonic coastal uplift and Quaternary sea-level fluctuations has resulted in the formation of marine terrace sequences, most of which were formed during separate interglacial highstands that can be correlated to marine isotope stages (MIS).

A marine terrace commonly retains a shoreline angle or inner edge, the slope inflection between the marine abrasion platform and the associated paleo sea-cliff. The shoreline angle represents the maximum shoreline of a transgression and therefore a paleo-sea level.

The platform of a marine terrace usually has a gradient between 1°–5° depending on the former tidal range with, commonly, a linear to concave profile. The width is quite variable, reaching up to 1,000 metres (3,300 ft), and seems to differ between the northern and southern hemispheres. The cliff faces that delimit the platform can vary in steepness depending on the relative roles of marine and subaerial processes. At the intersection of the former shore (wave-cut/abrasion-) platform and the rising cliff face the platform commonly retains a shoreline angle or inner edge (notch) that indicates the location of the shoreline at the time of maximum sea ingression and therefore a paleo-sea level. Sub-horizontal platforms usually terminate in a low tide cliff, and it is believed that the occurrence of these platforms depends on tidal activity. Marine terraces can extend for several tens of kilometers parallel to the coast.

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