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Shoreline & Near-shore Environments

Ripple marks on sand and in rock.

Ripple marks on sand and in rock.

Beaches occur between the high and low tide marks. Many wave-washed beaches are sandy, with symmetrical ripple-marks like those in the photo. Ripple-marks are often seen in sandstones that were originally formed on beaches (far right).

Spits & bars form where waves build up sand banks near to the shore or across river mouths (e.g.Humber estuary, UK).
Tidal flats in Cheshire

Tidal flats in Cheshire

Tidal flats occur in more sheltered lagoons and estuaries where calmer water deposits fine silt and clay. Being rich in nutrients and burrowing organisms, tidal flats attract sea birds.

Diego Garcia Atoll in the Pacific ocean Diego Garcia Atoll in the Pacific ocean. The lagoon is almost surrounded by reefs. The US airbase (left) gives an idea of size.
Logoon diagram

Tropical reefs and lagoons:

Reefs are wave-resistant, rocky structures, made up of the skeletons of organisms such as corals. Most modern reefs are in warm, clear, shallow, tropical seas, between the latitudes of 30oN and 30oS of the equator. Atolls are ring-like reefs surrounding a central lagoon (see photo).

Lagoons are areas of shallow sea sheltered by offshore sand bars or by coral reefs. Near-shore lagoons in cooler seas are usually dominated by muddy clay, but tropical lagoons sheltered by coral reefs are dominated by organic and chemical deposition of calcium carbonate that eventually forms limestone.
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