Page 346 - Fundamentals of Geomorphology

COASTAL LANDSCAPES 329

they form when waves approach at right-angles to the behind its neighbour. These are called headland bay
shore, although a few think that oblique waves cause beaches,or fish-hook beaches,or zetaform beaches,
them. Their mode of formation is disputed, and they owing to their likeness in plan-view to the Greek letter
havebeenvariouslyregardedasdepositionalfeatures,ero- zeta, ζ (Figure 13.10).
sional features, or features resulting from a combination
of erosion and deposition. Spits, barriers, and related forms
Inner and outer crescentic bars are sometimes
called rhythmic topography. They have wavelengths Accumulation landforms occur where the deposition
of 100–2,000 m, although the majority are somewhere of sediment is favoured (Figure 13.9). Suitable sites
between 200 and 500 m. Inner bars are short-lived and include places where obstructions interrupt longshore
associated with rip currents and cell circulations. Their flow, where the coast abruptly changes direction, and
horns often extend across surf-zone shoals into very large in sheltered zones (‘wave shadows’) between islands and
shoreline cusps known as sand waves, which lie parallel the mainland. Accumulation landforms are multifarious.
to the shore and have wavelengths of about 200–300 m. They may be simply classified by their degree of attach-
Outer crescentic bars may be detached from the shore ment to the land (Table 13.1). Beaches attached to the
and are more stable than inner crescentic bars. land at one end are spits of different types and forelands.
Many coasts display an orderly sequence of capes Spits are longer than they are wide, while forelands are
and bays. The bays usually contain bayhead or pocket wider than they are long. Beaches that are attached to the
beaches (Figure 13.9). In some places, including parts land at two ends are looped barriers and cuspate bar-
of the east coast of Australia, asymmetrically curved bays riers, tombolos, and barrier beaches. Beaches detached
link each headland, with each beach section recessed from the land are barrier islands.

Beach

Paired
Foreland spits

Arrow
Lagoon
Tombolo
Spit
Beach
barrier
Longshore
currents
Recurved
Comet-tail spit
spit
Looped
barrier

Figure 13.9 Depositional coastal landforms, shown diagrammatically.