Coastlines- ultimate interface between ocean and land
Portion of land affected by ocean processes
Zone of interaction between man and ocean
74% of US population lives w/in 50 mi of coast (incl. Great Lakes)
Shore-place where ocean and land meet- strictly area w/in tidal range
Coast-- more general term- entire portion of land area affected by
marine processes (estuaries, beach cliffs, dunes)
Look over the pictures in the text to get a sense of the wide range of coastlines and why they vary.
I. Sea Level
Global vs. local variations
A. Global-
1. vary amount of water in the ocean (glacials)- largest variations
2. vary size of the ocean basins (sea floor spreading rates)
3. vary volume occupied by water- temperature dependent
B. Local -
1. tectonic movement – tectonic uplift or lowering
2. loading- adding or removing weight- sediment, ice…
Due to local effect sea level can be rising in some places and falling
in others
As sea level changes the position of the coast changes (see Fig. 11.1)
II. Classifications
Variety of classifications:
* Whether sea level rising or falling
* Descriptive- volcanic, deltaic, reef, etc
* Erosional vs. Depositional- dominated by erosional or depositional
processes and features
* Whether land or ocean processes dominate (Primary vs secondary)-
used in your text
Primary = landscape formation dominated by terrestrial processes
Secondary = landscape formation dominated by marine processs
Just classifications- don't get bogged down in the details
A. Primary Coasts
Often rough and irregular, haven't been smoothed by ocean processes
Features produced by:
- change of sea level
- glacial activity
- sediment deposition at the mouth of a river
- volcanic acticity
- earthquake faults
1. Fjords- Common in Scandinavian Countries- U-shaped valleys
cut by glaciers when sea level was much lower
2. Estuaries- river valleys during glacial times, drown when
sea level rose (Chesapeake Bay)
3. Deltas- large piles of sediment transported to the ocean
by a river, deposited when the river enters the ocean (Mississippi, Nile)
4. Volcanic coasts- example- Hawaii
5. Faulted coasts- regions where faulting has uplifted or down
dropped the coastal region, often find beach terraces (California)
B. Secondary Coasts
Shaped by wave erosion, marine life
Can be characterized as erosional or depositional
1. Erosional- rocky shorelines, sea cliffs, headlands,
sea caves, arches, sea stacks
2. Depositional- sand spits, bay mouth bars, barrier islands
(see definitions in the textbook)
III. Anatomy of a Beach (secondary coast)
Beaches- zone of unconsolidated sediment (sand) along the shore
Dynamic environments= "River of Sand", "The Beaches are Moving"
most of the sand is just passing through, constant motion
A. Beach Composition
Size and type of sediment varies with energy and source
Source- river sand, coral fragments, volcanic rock, beach cliff material
Energy- higher energy moves larger particles (function of waves and
tides)
B. Beach Profiles
Typical profile (Fig. 11.13), varies with energy (season)
Berm- buildup of sand parallel to shore, at normal limit of sand
deposition by wave activity- us. marks high tide
Winter = higher energy (more storms) -> larger berms
Beach Scarp- Steep slope where wave action has cut into the
berm. Coincides with high water level
Low Tide Terrace—Flat area below the low tide level. Area where
waves expend most of their energy
Longshore Troughs- depression below the low tide level, runs
parallel to shore, can be cut by the longshore current
Long shore Bars—accumulation of sand that parallels the
shoreline. Can migrate on and offshore under different conditions (energy)
Usually migrate onshore during the summer (lower energy) and offshore and
build up higher during winter (higher energy)
C. Seasonal Profiles (Fig. 11.14)
Summer Profile- lower energy, gentle waves. Move sand up onto
the beach.
Winter Profile- higher energy (storms), more erosion. Transports
sand offshore. Creates larger berms inland
IV. Beach Processes
A. Wave action
Swash- wave moving onto beach, energy from waves
Backwash- return flow due to gravity
- if water percolates into beach sediment, less energy during return,
buildups steeper beach,
- if backwash strong- removes most of the new sediment- flatter beach
More water can percolate into beach when material coarser
coarse beaches us. steeper than fine grained beaches
Both swash and backwash can transport sediment in a zigzag pattern (Fig. 11.12)
B. Currents
Waves tend to approach beach at an angle
Longshore current- (Fig. 11.12) waves generally approach beach at an angle, energy is propogated down the beach int he direction the waves are headed, sets up current
C. Longshore Drift (Fig. 11.12)
-Transportation of sediment down the beach by:
* the longshore current- wave action stirs up the sediment, the current
moves it
plus
* waves- swash/backwash in zigzag pattern
D. Rip Currents (Fig. 11.31)
In very shallow water, water moves onshore with the waves. Also
transported along shore by the current.
When onshore motion builds up water faster than along shore can move
it, the water returns to the ocean in a focused current that cuts through
the surf zone
Rip currents – rapid seaward flow of water.
Indications of rip current
depression on beach
smaller waves
murky water (carries sediment)
Swim parallel to beach, or get carried beyond surf zone where rip loses
energy
E. Coastal Cells
Along a beach there is a balance between sources of sediment (inputs)
and areas where sediment is removed (outputs).
If inputs are greater = deposition
If outputs are greater = erosion
Inputs-
- Erosion of cliffs, dunes, or headlands
- river sediment
- longshore drift
Outputs
- into bays, estuaries
- down submarine canyons
- offshore- out rip currents or down slope
- into dunes
- longshore drift
A coastal Cell is a region of the beach over which inputs are balanced
by outputs