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Oceanography Chp. 10

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Composition of beaches
locally available material, may be coarse or fine, significant biological material at tropical beaches
Swash and backwash
sand movement perpendicular to shoreline (toward and away)
Longshore current
sand movement parallel to shoreline (up-coast or down-coast), wave refraction causes water and sand to move parallel to shore, zigzag motion in surf zone
Longshore transport
tons of sediment moved yearly, direction of transport changes due to wave approach
Swash
after wave breaks, uprush of water onto beach, sediment moved toward land
Backwash
water returns to ocean, sediment moved away from shore
Light wave activity
swash dominates and sediment is moved toward shore, wider beaches
Heavy wave activity
backwash dominates and sediment is moved away from shore, narrower beach
Erosional shorelines
marked by well-developed cliffs and recent tectonic activity
Wave erosion
increases w/ more shore exposed to open ocean, smaller tidal range and weaker bedrock
Barrier islands
long, narrow offshore deposits parallel to shore, common on East and Gulf coasts of U.S. and protect mainland from high wave activity (depositional shorelines)
Characteristics of barrier islands
movement landward over time, associated w/ rising sea levels, older peat deposits found on ocean beach
Deltas
river sediments reworked by ocean processes: waves, tides; distributaries carry sediment to ocean
Depositional shorelines
primarily deposited by longshore drift
Emerging shorelines
shorelines above current sea level, Marine terraces
Submerging shorelines
shoreline below current sea level, drowned beaches, submerged dune topography, drowned river valleys
Causes of changing sea level
local tectonic processes, i.e. Pacific coast of U.S. and active plate margin
changes in sea floor spreading rates, lake buildup or destruction, change of ice volumes (400 ft.) change in sea level
Global warming and changing sea level
if global warming continues, sea level will rise
Atlantic Coast
most coasts open to wave attack, barrier islands and drowned river valleys common
2.6 feet average erosion per year
Gulf Coast
low tidal range and generally low wave energy, tectonic subsidence and Mississippi delta dominates
6 feet average erosion per year
Pacific Coast
tectonically rising, open exposure to high energy waves
.016 average erosion per year
Hard stabilization
structures built to decrease coastal erosion and interfere w/ sand movement, often results in unwanted outcomes
Hard stabilization techniques
groins and groin fields
jetties
breakwaters
seawalls
Alternatives to hard stabilization
limit building near shorelines and continually add sand to beaches affected by longshore current
relocation