Headlands and bays are two related features of the coastal environment.
Contents 1 Geology and geography 2 Beach stability 3 Notes 4 External links // Geology and geographyHeadlands and bays are often found together on the same stretch of coastline. A bay is surrounded by land on three sides, whereas a headland is 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 (and often wind) activity than the water outside the bay, and typically have sandy beaches. Headlands and bays form on discordant coastlines, where bands of rock of alternating resistance run perpendicular to the coast. Bays form where weak (less resistant) rocks (such as sands and clays) are eroded, leaving bands of stronger (more resistant) rocks (such as chalk, limestone, granite) forming a headland, or peninsula. This difference in the rate of erosion is caused by differential erosion. 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 dissipating wave energy in the bays.1 In the formation of sea cliffs, wave erosion undercuts the slopes at the shoreline and they retreat landward. This creases 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 removed by the waves, usually during storms where wave energy is greatest. This debris provides sediment, 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 then start the same process all over again.
Beach stabilityBeaches 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 off the ocean have little land extending into it.
Notes ^ a b Easterbrook, D. (1999). "Surface Processes and Landforms: Second Edition". Prentice Hall]. ^ Link test. ^ Schwartz, M. (2005). "Encyclopedia of Coastal Science" . Springer. ISBN 13 978-1-4020-1903-6 p399 ^ a b Benedet, L., Klein, A., and Hsu, J. (2004). "Practical Insights and Applications of Empirical Bay Shape Equations". ICCE. External links GeoResources - diagrams of headland and bay formation v • d • e Coastal geography Landforms Anchialine pool · Avulsion · Archipelago · Atoll · Ayre · Barrier bar · Barrier island · Bay · Baymouth bar · Bight · Brackish marsh · Cape · Channel · Cliff · Cliff-top dune · Coast · Coastal plain · Coastal waterfall · Continental margin · Continental shelf · Coral reef · Cove · Dune · Estuary · Firth · Fjard · Freshwater marsh · Fundus · Geo · Gulf · Headland · Inlet · Intertidal wetland · Island · Islet · Isthmus · Lagoon · Marine terrace · Mouth bar · Raised shorelines · Machair · Mega delta · Mudflat · Natural arch · Peninsula · Reef · Ria · River delta · Salt marsh · Shore · Sound · Stack · Strait · Strand plain · Submarine canyon · Tied island · Tidal island · Tidal marsh · Tide pool · Tombolo · More... Beaches Beach cusps · Beach evolution · Beach ridge · Beachrock · Modern recession of beaches · Pocket beach · Raised beach · Shingle beach Processes Blowhole · Coastal erosion · Concordant coastline · Current · Cuspate foreland · Discordant coastline · Emergent coastline · Feeder bluff · Fetch · Headlands and bays · Large scale coastal behaviour · Longshore drift · Marine regression · Marine transgression · Rip current · Sea cave · Shoal · Spit · Submergent coastline · Surf break · Surge channel · Swash · Volcanic arc · Wave-cut platform · Wave shoaling · Wind wave · Wrack zone Management Coastal management · Accretion · Integrated coastal zone management · Submersion Related Bulkhead line · Coastline length · Intertidal zone · Littoral zone · Particle size (Shingle · Sand · Silt) · Physical oceanography · Region of freshwater influence · More...
