Page 350 - Fundamentals of Geomorphology

COASTAL LANDSCAPES 333

be tens of metres wide, a few metres high, and sev- form in coasts with high wave energy as the fine-grained
eral kilometres long. Beach ridge plains may consist of sediments needed for their growth are carried offshore
200 individual ridges and intervening swales. (Figure 13.13).
Cheniers are low and long ridges of sand, shelly sand,
and gravel surrounded by low-lying mudflats or marshes. Coastal sand dunes
They were first described from south-western Louisiana
and south-eastern Texas, USA, where five major sets of Coastal dunes are heaps of windblown sediment
ridges sit on a 200-km-long and 20–30-km-wide plain. deposited at the edge of large lakes and seas. With few
These ridges bear rich vegetation and are settled by exceptions, they are made from sediment blown off a
people. The word ‘chenier’ is from a Cajun expression beach to accumulate in areas sheltered from the action
originating from the French word for oak (chêne), which of waves and currents. Small, crescentic dune fields often
speciesdominatesthecrestsofthehigherridges.Cheniers form at the back of bays enclosed by rocky headlands,
can be up to 1 km wide, 100 km long, and 6 m high. while larger prograding dune fields form on straight,
Chenierplainsconsistoftwoormoreridgeswithmarshy sandy coasts that are exposed to prevailing and dominant
or muddy sediments between. Most cheniers are found onshore winds. They shield the land from extreme waves
in tropical and subtropical regions, but they can occur in and tides and are stores of sediment that may replenish
a wide range of climates (Figure 13.12). They cannot beaches during and after storms. Dunes may also occur

Cheniers
Presumed
cheniers

Figure 13.12 World distribution of cheniers.
Source: Adapted from Augustinus (1989)