Page 408 - Laboratory Manual in Physical Geology

ACTIVITY and whether the position of the coastline is advancing or
receding. A coastline cannot advance seaward if it lacks
15.1 Coastline Inquiry a supply of sediment to do so. Some sediment may be
eroded from the land itself, as when waves undercut a

cliff and rocks collapse into the water.
THINK | What factors affect the shape and ■ Waves carry sediment onto beaches when they are
About It position of shorelines? gentle ( low energy waves ), but they remove sediment
from beaches and erode the land when they are large
OBJECTIVE Compare and contrast photographs and forceful ( high energy waves ). Particles moved by
of coastlines and determine what factors primarily waves and blasted against rocky surfaces will cause
aff ect them. abrasion (smoothing and wearing down of the rocky
surfaces). The direction of the waves is a factor in what
PROCEDURES
direction sediment is moved and what parts of a coast-
1. Before you begin , read the Introduction and line are eroded the most.
Dynamic Natural Coastlines below. Also, this is ■ Wind interacts with the surface of the water to gener-
what you will need: ate the waves and blows beach sand into dune forms
____ Activity 15.1 Worksheet (p. 385 ) and pencil on the adjacent land.
2. Complete the worksheet in a way that makes ■ Currents running along the coastline ( longshore currents ),
sense to you. in streams reaching the coastline ( stream currents on
deltas ), and back-and-forth through coastal environments
3. After you complete the worksheet , be prepared ( tidal currents ) move sediment about and redeposit it on
to discuss your observations and classifi cation beaches, sand bars and spits, and tidal flats.
with other geologists.
■ Storms are highly energized systems, so they are
one of the main factors that determines the shape of
coastal landforms. A single storm, like a hurricane,
can significantly erode one part of a coastline and
Dynamic Natural Shorelines deposit a large volume of sediment on another part
of the coastline.
Some examples of shorelines are pictured in FIGURE 15.1 . ■ Organisms (including humans) modify their enviro-
In each case, the land is acted upon by water, wind, organ- ment. Corals construct reefs that armor the coastline
isms, and sometimes ice, in ways that vary in both inten- against erosion. Marsh plants and mangroves trap and
sity and time. For example, there is constant water and air bind sediment with their roots and absorb the energy of
motion, but their intensities vary throughout the day in storms. Humans use a variety of methods to preserve and
relation to tides and the weather. At one part of the day or build up coastlines, but they also destroy marshes and
year, the erosional processes (those that remove sediment reefs and otherwise degrade elements of the coastline.
and cut into rock, reefs, and marshes) may be dominant
over the depositional processes (those that cause sediment
to accumulate and marshes or reefs to grow). At another
part of the day or year, the depositional processes may be
dominant over the erosional ones. Over longer periods ACTIVITY
of time, one or the other process (erosion or deposition)
is generally dominant, so most coastlines are either 15.2 Introduction to Shorelines
receding (moving landward, eroding back) or advancing
(building seaward). THINK What factors affect the shape and
About It position of shorelines?
Factors Affecting Coastlines

There are many specific factors that affect the shapes of OBJECTIVE Identify and interpret natural shoreline
coastal landforms and the overall positions of coastlines, landforms and distinguish between emergent and
but here are some of the most important factors: submergent shorelines.
■ What the land is made of determines how much the PROCEDURES
agents of change must work on the land to shape it. 1. Before you begin , read Submergent vs. Emergent
The land may be hard rock, clay, sand, large loose Coastlines below. Also, this is what you will need :
rocks, or a combination of these. The land may also ___ ruler, calculator
be “armored” with large boulders (called “rip rap”) or ___ Activity 15.2 Worksheets (pp. 386–387 ) and
rigid concrete structures added by humans. pencil
■ Supply of sediment carried to a specific location along
a coastline by rivers, coastal currents, or people often 2. Then follow your instructor’s directions for
determines whether the coastline is sandy or of bare rock completing the worksheets.

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