Coastal Landforms
Basic Concepts
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
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
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
COASTAL FLUVIAL PROCESSES/LANDFORMS
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
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.
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.
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 mainland to an island
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
Tides
Tides
Tides