Page 413 - Laboratory Manual in Physical Geology

■ Delta —a sediment deposit at the mouth of a river where Human Modification of Shorelines
it enters an ocean or lake. (emergent, FIGURE 15.2 ).

■ Headland with cliffs —projection of land that extends Humans build several common types of coastal structures
into an ocean or lake and generally has cliffs along its in order to protect harbors, build up sandy beaches, or

water boundary (submergent, FIGURE 15.3 ). extend the shoreline. Study the following four kinds of
■ Spit —a sand bar extending from the end of structures and their effects in FIGURE 15.6 .
a beach into the mouth of an adjacent bay ■ Sea wall—an embankment of boulders, reinforced
(emergent, FIGURE 15.2 ). concrete, or other material constructed against a shore-

■ Tidal flat —muddy or sandy area that is covered with line to prevent erosion by waves and currents.
water at high tide and exposed at low tide. Tidal flats
are best developed along emergent coastlines. ■ Breakwater—an offshore wall constructed parallel
■ Saltmarsh —a marsh that is flooded by ocean water to a shoreline to break waves. The longshore current
at high tide. Saltmarshes are best developed along is halted behind such walls, so the sand accumulates
emergent coastlines ( FIGURE 15.2 ). there and the beach widens. Where the breakwater is

■ Wave-cut cliff (or sea cliff )—a seaward-facing cliff used to protect a harbor from currents and waves, sand
along a steep shoreline, produced by wave erosion. often collects behind the breakwater and may have to
Wave-cut cliffs are best developed along submergent be dredged.
coastlines ( FIGURE 15.3 ). ■ Groin (or groyne)—a short wall constructed perpen-
■ Wave-cut platform —a bench or shelf at sea level dicular to shoreline in order to trap sand and make or
(or lake level) along a steep shore, and formed by build up a beach. Sand accumulates on the up-current
wave erosion. Wave-cut platforms are best developed side of the groin in relation to the longshore current.
along emergent coastlines ( FIGURE 15.2 ).

■ Marine terrace —an elevated wave-cut platform that ■ Jetties—long walls extending from shore at the
is bounded on its seaward side by a cliff or steep slope mouths of harbors and used to protect the harbor
(and formed when a wave-cut platform is elevated by entrance from filling with sand or being eroded by
uplift or regression; emergent coastline, FIGURE 15.2 ). waves and currents. Jetties are usually constructed of

■ Stack —an isolated rocky island near a headland boulders and in pairs (one on each side of a harbor or
cliff, best developed along submergent coastlines inlet).
( FIGURE 15.3 ).

■ Tombolo —a sand bar that connects an island
with the mainland or another island. Tombolos
are best developed along submergent coastlines ACTIVITY
( FIGURE 15.3 ).
■ Tied island —an island connected to the mainland 15.4 The Threat of Rising Seas
or another island by a tombolo (usually submergent,
FIGURE 15.3 ).

THINK How will rising sea levels affect
ACTIVITY About It | communities along shorelines?

15.3 Shoreline Modification at OBJECTIVE Describe the probability of global
Ocean City, Maryland sea-level rise and analyze the coastal hazards and
increased risks it may cause.
THINK | How successful are efforts to protect PROCEDURES
About It shorelines from erosion by building 1. Before you begin , read The Threat of Rising Seas
artificial structures? below. Also, this is what you will need :
___ calculator

OBJECTIVE Identify the common types of artifi cial ___ Activity 15.4 Worksheet (p. 390 ) and pencil
structures used to modify shorelines and explain their

effects on coastal environments. 2. Then follow your instructor’s directions for
completing the worksheets.
PROCEDURES
1. Before you begin , read Human Modifi cation of
Shorelines below. Also, this is what you will need : The Threat of Rising Seas
___ ruler, calculator The National Oceanic and Atmospheric Administration
___ Activity 15.3 Worksheets (pp. 388–389 ) and (NOAA), using measurements from satellite radar
pencil altimeters, estimates that global sea level has been rising
2. Then follow your instructor’s directions for at a rate of 2.9 mm/yr since 1992. Meanwhile, a 2013
completing the worksheets. report by Working Group 1 of the Intergovernmental

Coastal Processes, Landforms, Hazards, and Risks ■ 381