Coastal Processesand LandformsCoastal Processesand Landforms
The Coastal EnvironmentThe Coastal Environment
The World Ocean covers 71% of Earth’s surface, and the world’s
shoreline is of enormous length
Earth’s coastlines have tremendous resource, and they are
biologically and geomorphically diverse
Their spectacular scenery bring in more tourists than any other
natural environment, and continue to attract new residents
But they are also subject to any array of natural hazards, and
human-induced environmental problems; ironically, some of
our most polluted waters are found in coastal locations
Global warming and resulting sea level rise will have profound
consequences for coastal zones
The Coastal Zone: DefinitionsThe Coastal Zone: Definitions
Coastal Zone: General region of interaction between the landand the ocean
Shoreline or Coastline: Constantly changing contactbetween the ocean surface and the dry land
Sea Level: Average position of the ocean shoreline fromwhich all elevations are measured
Swash: The thin sheet of water rushing towards the shoreline
Backwash: The return flow of water to the ocean
Nearshore Zone: Comprises Breaker Zone, Surf Zone and
Swash Zone (See Fig. 17.1, p. 407 in Text)
Offshore Zone: Undefined zone seaward, beyond thebreaker zone
Continental Shelf and Continental SlopeContinental Shelf and Continental Slope
Waves : are travelling, repeating forms of alternating highs and lowscalled wave crests and wave troughs – induced by Wind
Currents : horizontal movement of ocean water, usually in response toatmospheric circulation also, rip currents, long shore currents
Waves and CurrentsWaves and Currents
Wave Refraction – waves change directional trendas they approach shore.
Raglan, New Zealand
Basic ConceptsBasic Concepts
I.Repeated sea level changes in the past
• Estimated 422 ft. rise since 18,000 years ago
• specific landscapes submergent (Passive) oremergent (Active) depending on tectonic change
II. Waves and resultant currents erode, transport, anddeposit sediment load.
• rocky headlands
• beaches
III. Tides affect all coastal life but have littletopographic effect.
• tidal bore/tidal wave/tsunami
Submergent vs. Emergent CoastlinesSubmergent vs. Emergent Coastlines
• During the ice ages (or glacial periods) sea level sinks asmore water is tied up in glaciers• During the ice ages (or glacial periods) sea level sinks asmore water is tied up in glaciers
• During interglacial periods sea level rises, flooding manyriver valleys, creating bays and estuaries• During interglacial periods sea level rises, flooding manyriver valleys, creating bays and estuaries
• • Submergent Coastlines Rias: drowned river valleys;
Fjords: drowned glacial valleys
• Sea levels rise also causes many features of the formershore lie underwater
• Also known as Passive-margin Coasts – e.g., AtlanticCoast – because tectonic activity occurs in the middleof the ocean, and the coast is tectonically passive.
SubmergentCoastlines
Sea level riseinundated manycoastal valleyscreating bays andestuaries. Thesecoasts are oftenreferred to as Riacoastlines.
Estuary – An armof the sea thatextends inland i.e.,an inlet) to meetthe mouth of a river.
Emergent Coastlineswhere water level has fallen, or land has risen due to tectonic activity
Tectonic forces lift coastlines faster than sea-level rises. Dramatic seacliffs and marine terraces tower above the sea. Also, sea stacks.
Most activity occurs along active subduction zones and transform plate boundaries.
In areas with“rapid” tectonicuplift,EmergentCoastlines andcliffs arecommon, andbays are rareIn areas with“rapid” tectonicuplift,EmergentCoastlines andcliffs arecommon, andbays are rare
Also called Active-margin Coast – e.g.,Pacific Coast
COASTAL PROCESSES AND LANDFORMSCOASTAL PROCESSES AND LANDFORMS
Coastal Erosion – dependent on wave size, angle, andfrequency. Focused where waves contact coastline.
• Headlands, sea cliffs, bluffs, sea stacks, natural bridges
• Beach Erosion
Coastal Transportation – Large waves move beach sandoffshore. Small waves push it back onshore.
• Wave action creates strong currents parallel to shore –Longshore currents, and longshore drifting.
Also Littoral drifting and beach drifting.
Coastal Deposition – where wave action is reduced,beaches and dunes form.
• Beaches, dunes, sand spits
Coastal ErosionCoastal Erosion
Hydraulic action: Sheer physical force, thepounding of waves against coastal rockmaterial.
Abrasion: The process of wearing down orrubbing away by means of friction.
Isla Vista Beach, October 2001
Isla Vista Beach, December 2002
Beach Erosion
Formation
of
Marine
Terrace
Marine Terraces
Point Reyes National SeashoreCalifornia
Sea StacksPort Campbell National Park, Victoria, Australia
Natural Bridges and Arches Port Campbell National Park, Victoria, Australia
Erosional LandformsErosional Landforms
1.Sea Cliffs: When Waves pound directly against steepland
2.Sea Caves: Erosion, corrosion and hydraulic actionalong lines of weakness
3.Sea Arches: 2 caves meet from each side of hydraulicaction of a headland
4.Sea Stacks: A resistant pillar is left standing – theremnant is called a sea stack
5.Marine Terraces: Formed by tectonic activity uplift outof reaches of wave action
6.Headlands: Prortruded land, flanked by receding bays
Depositional LandformsDepositional Landforms
1.Beach: Landform of coastal deposition, continuous withthe mainland Sandy beaches, Pebble andboulder beaches, White coral reef beaches, Blacksandy beaches – in volcanic Big Island, Hawaii
2. Spits: Coastal depositional landforms connected to themainland at just one end
3. Barrier beaches: long depositional feature constructedparallel to mainland, protection from direct waveattack
4. Lagoon: Body of water partially or fully enclosed bybaymouth bar
5. Tombolo: Strip of sediment connecting mainland to anisland
Tombolo
Tombolo
Sand Spit
Sand Spit
Barrier Islands
Barrier Islands
Point ReyesNationalSeashore,California
Point Reyes Lighthouse
IslandsIslands
Types of Islands
1.Continental Islands – separated frommainland due to shore submergence
2.Oceanic Islands – volcanic islands
2. Atoll – coral formation
Tropical CoastsTropical Coasts
Factors Correlated with HealthyCoral Reef Growth
Factors Correlated with HealthyCoral Reef Growth
•Water temperature range: 18 – 29C
•Normal seawater salinity: 32 – 35 ‰
•Clear, transparent water
•Little or no sedimentation
•Vigorous water motion
Tropical Mangroves
Mangroves create tidal forests. These rich ecosystems providehabitat for countless creatures and help to stabilize and, bycatching sediment, even create coastline.
Tides
Low Tide, New Brunswick
TidesTide Cycle
Tides rise and fall with the rising moon, an interval of24 hours and 50 minutes. There is a bulge on both sidesof 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.
TidesTide Range
Tide range dependent onrelative position of earth,moon, and sun.
Spring Tides - highesttidal range
Neap Tides - lowest tidalrange
Occurs every 2 weeks
Tidal Patterns in the U.S.
TidesTides
Not significant as a geomorphic agent, but can be very consequentialwhen coinciding with storm surges or tsunamis
