Page 544 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

508 part III The earth–atmosphere interface
(a) Arch, Ascension Island, Atlantic Ocean.
(b) Wave-cut platform, Monterey County, California.
Former sea cliffs
Sea arch
Terrace
Wave-cut platform (terrace)
Sea cliff
Notched cliff
(d) Notched cliff, Bear Island, Barents Sea.
Sea cave
Landslides
Sea stack
(c) Stacks, and headland, Gough Island, South Atlantic Ocean.
(e) Collapsing limestone cliffs at the Twelve Apostles, Victoria, Australia.
▲Figure 16.13 Erosional coastal landforms. [(a)–(d) Bobbé Christopherson. (e) Philip giles.]
Gulf coastal plains of the United States, which lie along the relatively passive, trailing edge of the North American lithospheric plate. Although the landforms are generally classified as depositional along such coastlines, erosional processes are also at work, especially during storms.
Figure 16.14 illustrates characteristic landforms de- posited by waves and currents. Barrier spits consist of material deposited in a long ridge extending from a coast, sometimes partially crossing and blocking the mouth of a bay (Figure 16.14a and b). Classic examples of barrier spits are found on the shores of the Gulf of St. Lawrence in New Brunswick and Nova Scotia, and on the Magdalen Islands in the middle of the Gulf.
If a spit grows to completely cut off the bay from the ocean, it becomes a bay barrier, or baymouth bar. Spits
and barriers are made up of materials transported by lit- toral drift. For sediment to accumulate, offshore currents must be weak, since strong currents carry material away before it can be deposited. Bay barriers often surround an inland lagoon, a shallow saltwater body that is cut off from the ocean. A tombolo occurs when sediment depos- its connect the shoreline with an offshore island or sea stack by accumulating on an underwater wave-built ter- race (Figure 16.14c).
Beaches Of all the depositional landforms along coast- lines, beaches probably are the most familiar. Techni- cally, a beach is the relatively narrow strip along a coast where sediment is reworked and deposited by waves and currents. Sediment temporarily resides on the beach