Chapter 11 Flashcards
Coastal Zone
-Broad zone where continents meet oceans
-Different oceanic processes occur in this zone, mainly waves and tides.
Coastal Zone:Coastal processes occur ___(where) relative to what?
occur in restricted narrow zone relative to other geologic process such as rivers, wind and etc
(watch video)
Coastal Zone: coastal zones appear to migrate where? due to what?
landward or seaward due to changes
in sea level, uplift or subsidence, etc.
Coastal Zone: coastal zones change constantly, ___of world’s population is found in
coastal cities - because of their strong appeal
2/3
EX.New York, Los Angeles, New Orleans, Tokyo, London, Rio de Lenerio,
Shanghai, Sidney, Cicily, Lagos, etc.
(look at pic of america)
Types of coasts: Two Types: Cliff Coasts:
Ocean in contact with shallow/narrow beach
-Usually bounded by cliffs
-Such coasts found mainly in subduction zones:
-E.g., in Oregon, Washington State, California
- Close to active margins of geologic activity
Types of coasts: Two Types: Barrier Coasts:
Main land NOT in contact with ocean directly
Ocean -> barrier island -> lagoon -> main land
-Usually mainly passive margins where there is no tectonic activity
Coastal Zone Processes: Tides
ONCE or TWICE daily, ocean water level falls and rises due to gravitational attraction
of moon
-fluctuations of sea level are TIDES
-more and more shoreline flooded during sea level rise (Flood or High Tide)
-Accompanying fall is EBB or LOW TIDE.
—Rise found to be few cm to 15 m
Coastal Zone Processes: Waves
Waves are the dominant force driving the nature of a beach. The energy carried through waves moves beach sediment and transforms beach shape.
-Are agents of erosion, transportation & deposition(image on typical beach)
Coastal Zone Processes: Waves: Wave Gnerration:
-The wind transfers some energy to the water to produce waves.
-Causing the water surface to oscillate.
-As more wind blows, more waves are formed.
-Waves differ in size, e.g., during storms, waves are bigger
-Big waves have greater velocities
-Big waves can outrun small waves.
(image on typical beach)
*Wave Characteristics
-As a wave enters shallow water, it becomes oversteepened
-The wave crest advances faster than wave form.
-Crest then plunges forward as a BREAKER
Wave Characteristics: 2 types: Longshore Current
-Long, narrow currents perpendicular to direction of waves
- Important in transportation and deposition
(check picture)
Wave Characteristics: 2 types: Rip Currents
-Narrow surface currents out to sea through breaker zone
( check picture)
Deposition in Coastal Zones: Deposits include..?
Definition of beaches?
BEACHES, SPITS, BAYMOUTH, BARS and BARRIER BARS.
Beaches:
* Unconsolidated sediments extending landward from sea. - Different parts.
-Seasonal Changes in Beaches: Summer Beaches are
A.covered with sand generally
b. have wide berms (a gentle sloping beach face)
c. a smooth offshore profile
-Seasonal Changes in Beaches: Winter Beaches
Acoarser grained & steeper
b. have small berms or none
c. have sand bars parallel to shoreline
-Seasonal Changes in Beaches:*Change in shape is related wave intensity:
In winter, storm waves have more energy. Therefore, sand is eroded & transported from
beach offshore & retained as a sand bar. (check picture)
Seasonal Changes in Beaches:In summer, waves are more what?
waves are gentler
Seasonal Changes in Beaches:The same sand that was carried offshore winter
during winter is returned
onshore. Volume sand remains almost constant
Spits & Baymouth Bars:
-Next most common deposits to the beach
-Are variation of same feature
Spits & Baymouth Bars:A SPIT
is a continuation of a beach that projects in a body of water(picture)
Spits & Baymouth Bars: A BAYMOUTH BAR
is a spit that has grown to completely close off a BAY.
- Both result from longshore current lagoons.(picture)
Coastline Erosion:
In some coastlines, erosion dominates deposition.
-Here, Beaches are lacking
-Sea cliffs are common erosional features.
Due to the action of waves seacliffs retreat toward the land in response to:
CORROSION, HYDRAULIC ACTION or ABRASION
Coastline Erosion: Corrosion
the wearing away of rock by chemical processes
Coastline Erosion:Hydraulic action
erosion due to the forces of water.
Coastline Erosion:Abrasion
erosion from the grinding of rock & sand carried by waves
Coastline Erosion: The rate of retreat of seacliff may __ by ___?
be high at Cape Cod, Massachusetts, retreat was observed to be as much as 30 m per century. (picture)
Protection of Coastline :Construction of Structures: Jetties
- Structures extending seaward to protect bays from deposition due to longshore currents.
-Done to keep bays open to PLEASURE BOATING & COMMERCIAL SHIPPING
(Picture)
Protection of Coastline :Construction of Structures:Sea Wall
Protect people who live near beaches from the ocean.
-May collapse eventually.
-Expensive to construct.
Protection of Coastline :Construction of Structures: Rock revetments
Reinforcements with large blocks of rocks.
Protection of Coastline :Construction of Structures:Break Water
-Constructed to create quiet water around beach.
Protection of Coastline :Construction of Structures: Groins
-Constructed to trap sand in order to widen the beach(picture)
