Headlands and bays

Looking towards the Beachy Head cliffs and bay (East Sussex, England)

Headlands and bays are two related coastal features. Headlands and bays are often found on the same coastline. A bay is a body of water, either seawater (salt water) or fresh water, surrounded by land on three sides, whereas a headland is land surrounded by water on three sides. Headlands are characterized by high, breaking waves, rocky shores, intense erosion, and steep sea cliffs. Bays generally have less wave activity, and often less wind activity than the areas of water outside the bay, and typically have sandy beaches. Headlands and bays form on discordant coastlines, where the land consists of bands of rock of alternating resistance that run perpendicular to the coast.

Geology and geography[edit]

Bays form where weak, or less resistant rocks, such as sands and clays, are eroded, leaving bands of stronger, or more resistant rocks, such as chalk, limestone, and granite), which form a headland or peninsula. Refraction of waves occurs on headlands concentrating wave energy on them, so many other landforms, such as caves, natural arches, and stacks, form on headlands. Wave energy is directed at right angles to the wave crest, and lines drawn at right angles to the wave crest (orthogonals) represent the direction of energy expenditure. Orthogonals converge on headlands and diverge in bays, which concentrates wave energy on the headlands and dissipates wave energy in the bays.^[1]

In the formation of sea cliffs, wave erosion undercuts the slopes at the shoreline, which retreat landward. This increases the shear stress in the cliff-forming material and accelerates mass movement.^[1] The debris from these landslides collects at the base of the cliff and is also removed by the waves, usually during storms, when wave energy is greatest. This debris provides sediment, which is transported through longshore current for the nearby bay. Joints in the headlands are eroded back to form caves, which erode further to form arches. These gaps eventually collapse and leave tall stacks at the ends of the headlands. Eventually these too are eroded by the waves.^[2]

Wave refraction disperses wave energy through the bay, and along with the sheltering effect of the headlands this protects bays from storms. This effect means that the waves reaching the shore in a bay are weaker than the waves reaching the headland, and the bay is thus a safer place for water activities like surfing or swimming. Through the deposition of sediment within the bay and the erosion of the headlands, coastlines eventually straighten out. But then the same process starts all over again.

Beach stability[edit]

Beaches are dynamic geologic features that can fluctuate between advancement and retreat of sediment. The natural agents of fluctuation include waves, tides, currents, and winds. Man-made elements such as the interruption of sediment supply, such as a dam, and withdrawal of fluid can also affect beach stabilization.^[3] A headland bay beach can be classified as being in three different states of sedimentation. Static equilibrium refers to a beach that is stable and does not experience littoral drift or sediment deposition or erosion.^[4] Waves generally diffract around the headland(s) and near the beach when the beach is in a state of static equilibrium. Dynamic equilibrium occurs when the beach sediments are deposited and eroded at approximately equal rates.^[4] Beaches that have dynamic equilibrium are usually near a river that supplies sediment and would otherwise erode away without the river supply. Unstable beaches are usually a result of human interaction, such as a breakwater or dammed river.^[4] Unstable beaches are reshaped by continual erosion or deposition and will continue to erode or deposit until a state of equilibrium is reached in the bay.

References[edit]

^ ^a^b Easterbrook, Don (1999). Surface Processes and Landforms (2nd ed.). Prentice Hall.

^ "Erosion and Deposition in Coastal Headlands". 2001. Retrieved 28 January 2016.

^ Schwartz, M. (2005). "Encyclopedia of Coastal Science" . Springer. ISBN 978-1-4020-1903-6 p399

^ ^a^b^c Benedet, L.; Klein, A. H. F.; Hsu, J. R.-C. (2004). Practical Insights and Applications of Empirical Bay Shape Equations. International Conference on Coastal Engineering 2004. Lisbon: American Society of Civil Engineers. pp. 2181–2193. doi:10.1142/9789812701916_0175. ISBN 978-981-256-298-2.

External links[edit]

GeoResources - diagrams of headland and bay formation

[Easterbrook-1] Easterbrook, Don (1999). Surface Processes and Landforms (2nd ed.). Prentice Hall.

[georesources-2] "Erosion and Deposition in Coastal Headlands". 2001. Retrieved 28 January 2016.

[3] Schwartz, M. (2005). "Encyclopedia of Coastal Science" . Springer. ISBN 978-1-4020-1903-6 p399

[Benedet-4] Benedet, L.; Klein, A. H. F.; Hsu, J. R.-C. (2004). Practical Insights and Applications of Empirical Bay Shape Equations. International Conference on Coastal Engineering 2004. Lisbon: American Society of Civil Engineers. pp. 2181–2193. doi:10.1142/9789812701916_0175. ISBN 978-981-256-298-2.

v t e Coastal geography
Landforms	Anchialine pool Archipelago Atoll Avulsion Ayre Barrier island Bay Baymouth bar Bight Bodden Brackish marsh Cape Channel Cliff Coast Coastal plain Coastal waterfall Continental margin Continental shelf Coral reef Cove Dune cliff-top Estuary Firth Fjard Fjord Freshwater marsh Fundus Gat Geo Gulf Gut Headland Inlet Intertidal wetland Island Islet Isthmus Lagoon Machair Marine terrace Mega delta Mouth bar Mudflat Natural arch Peninsula Reef Regressive delta Ria River delta Salt marsh Shoal Shore Skerry Sound Spit Stack Strait Strand plain Submarine canyon Tidal island Tidal marsh Tide pool Tied island Tombolo Windwatt
Beaches	Beach cusps Beach evolution Coastal morphodynamics Beach ridge Beachrock Pocket beach Raised beach Recession Shell beach Shingle beach Storm beach Wash margin
Processes	Blowhole Cliffed coast Coastal biogeomorphology Coastal erosion Concordant coastline Current Cuspate foreland Discordant coastline Emergent coastline Feeder bluff Fetch Flat coast Graded shoreline Headlands and bays Ingression coast Large-scale coastal behaviour Longshore drift Marine regression Marine transgression Raised shoreline Rip current Rocky shore Sea cave Sea foam Shoal Steep coast Submergent coastline Surf break Surf zone Surge channel Swash Undertow Volcanic arc Wave-cut platform Wave shoaling Wind wave Wrack zone
Management	Accretion Coastal management Integrated coastal zone management Submersion
Related	Bulkhead line Grain size boulder clay cobble granule pebble sand shingle silt Intertidal zone Littoral zone Physical oceanography Region of freshwater influence
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