Coastal
Landforms
Basic Concepts
I. Sea level changes repeatedly
• 422 ft. eustatic rise since 18,000 years ago.
denoting or relating to worldwide changes in sea level,
caused by the melting of ice sheets, movements of the
ocean floor, sedimentation, etc.[from Greek, from EU- +
STATIC]
• specific landscapes submergent or emergent
depending on tectonic change
II. Waves and resultant currents erode, transport, and
deposit sediment load.
• rocky headlands
• beaches
III. Tides affect all coastal life but have little
topographic effect.
The Coastal Zone
• Coastal Zone: General region of interaction
between the land and the ocean
• Shoreline: Constantly changing contact between
the ocean surface and the dry land.
• Swash: The thin sheet of water rushing towards
the shoreline
• Backwash: The return flow of water to the ocean
Eustatic Change and Submergent vs.
Emergent Coastlines
• during ice ages sea level sinks as ocean water
compresses and more water is tied up in glaciers.
• During interglacial periods sea level rises,
flooding many former river valleys creating bays
and estuaries.
• In areas with rapid tectonic uplift emergent
cliffs common and bays rare.
Coasts
1. Passive margin Coasts-Atlantic
Coast
Tectonic activity occurs in the middle of
the ocean. Coast is tectonically
passive.
2. Active margin Coast – Pacific Coast
Most activity occurs around the ocean
margin because of active subduction
and transform plate boundaries.
West Coast
• Coastlines of emergence: where
water level has fallen, or land has risen
due to tactonic activity
• Marine terraces, Sea Stacks, Sea cliffs
Emergent Coastlines
Tectonic forces
lift coastlines
faster than sealevel rises.
Dramatic cliffs
and marine
terraces tower
above the sea.
Coastlines of Submergence
• Sea levels rise due to retreate of
Pleistocene ice sheet and many features
of the former shore lie underwater
• Tactonic forces have lowered the level
of the land- San Franscisco Bay
• Submergent Coastlines
– Rias: river valleys are drowned
– Fjords: Glacial Valleys drowned
Submergent
Coastlines
Sea level rise inundated
many coastal valleys creating
bays and estuaries. These
coasts are referred to as
ria coastlines.
Estuary - An arm of the sea
that extends inland to meet
the mouth of a river.
COASTAL FLUVIAL PROCESSES/LANDFORMS
Coastal Erosion - dependent on wave size, angle, and
frequency. Focused where waves contact coast.
• Headlands, sea cliffs, bluffs, sea stacks, natural bridges
• Beach Erosion
•Coastal Transportation - wave action creates strong
currents parallel to shore. Large waves move beach sand
offshore. Small waves push it back on shore.
Coastal Deposition – where wave action is reduced,
beaches and dunes form.
• beaches
• dunes
• sand spits
Origin and Nature of Waves
• Waves : are travelling, repeating forms of
alternating highs and lows called Wave crests
and wave troughs
• Wave Height: The vertical distance
between a wave trough and wave crest
• Wave Length: Horizontal distance
between successive wave crests
• Tides: Two very long wavelength waves
caused by the interaction between Earth,
Moon and Sun
Fig. 20-24, p. 588
Coastal Erosion
• Corrosion: removal of ions, rock
forming minerls by solutions through
chemical weathering,
• Hydraulic action: Sheer physical
force, the pounding of waves against
coastal rock material.
• Abrasion: The process of wearing
down or rubbing away by means of
friction.
Isla Vista Beach, October 2001
Isla Vista Beach, December 2002
Beach Erosion
Coastal Erosion Landforms
1. Sea Cliffs: When Waves pound directly
against steep land
2. Sea Caves: Erosion, corrosion and hydraulic
action along lines of weakness
3. Sea Arches: 2 caves meet from each side of
hydraulic action of a headland
4. Sea Stacks: A resistant pillar is left standing
the remnant is called a sea stack
5. Marine Terraces: Formed by tectonic activity
uplift out of reaches of wave action
Marine Terraces
Point Reyes National Seashore
Wave Refraction - waves change
directional trend as they approach shore.
Raglan, New Zealand
Tombolo
Tombolo
Sand Spit
Sand Spit
Sea Stacks
Natural Bridges and
Arches
Depositional Landforms
1. Beach: Landform of coastal deposition
continuous with the mainland.
• Sandy beaches
• Pebble and boulder beaches
• White coral reef beaches
• Black sandy beaches- in volcanic big
island Hawaii
Longshore bars
• Spits: Coastal deposit landforms
connected to the mainland at just one
end
• Barrier beaches: long depositional
feature constructed parallel to
mainland, protection from direct wave
attack.
• Lagoon
• Tombolo: Strip of sediment connecting
Barrier Islands
Barrier Islands
Outer Banks, North Carolina
Tropical Coasts
Factors Correlated with
Healthy Coral Reef Growth
•
•
•
•
•
water temperature range: 18 – 29°C
normal seawater salinity: 32 – 35 ‰
clear, transparent water
little or no sedimentation
vigorous water motion
Tropical Mangroves
Mangroves create tidal forests. These rich ecosystems provide
habitat for countless creatures and help to stabilize and, by
catching sediment, even create coastline.
Tides
Tides rise and fall with the rising moon, an interval of
24 hours and 50 minutes. There is a bulge on both sides
of the earth. Thus two high tides each cycle.
Flood tide (low to high) takes 6:13 and then ebb tide
(back to low) is another 6:13.
Tides
Tide range dependent on
relative position of earth,
moon, and sun.
Spring Tides - highest
tidal range
Neap Tides - lowest tidal
range
Fig. 20-19, p. 581
Fig. 20-22, p. 584
Tides
Tide range dependent on
relative position of earth,
moon, and sun.
Full Moon
Spring Tides - highest
tides.
Neap Tides - lowest tides.
Half Moon
Fig. 20-25, p. 588
Tides
Low Tide, New Brunswick