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Headlands and bays: Wikis

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Headlands and bays are two related features of the coastal environment.

Contents

Geology and geography

Headlands 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 are typically quiet with 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 stability

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 off the ocean have have little land extending into it.

Notes

  1. ^ a b Easterbrook, D. (1999). "Surface Processes and Landforms: Second Edition". Prentice Hall].
  2. ^ Link test.
  3. ^ Schwartz, M. (2005). "Encyclopedia of Coastal Science" . Springer. ISBN 13 978-1-4020-1903-6 p399
  4. ^ a b Benedet, L., Klein, A., and Hsu, J. (2004). "Practical Insights and Applications of Empirical Bay Shape Equations". ICCE.

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Simple English

A headland is an area of land that is surrounded by water on three sides. A bay is a an area of water. It is surrounded by land on three sides. Very often, the land areas are called capes. The water areas are also called gulfs. Headlands are made of hard rock and bays are made of soft rock. It takes the hard rock longer to erode.

A bay is a hole in the land next to a sea or lake between two headlands. The waves coming to the shore in a bay are usually constructive waves, and because of this, many of them have a beach. A bay may be metres across, or it could be hundreds of kilometres across. Bays form where weak rocks, such as sands and clays, are eroded, leaving bands of stronger rocks, such as chalk, limestone, or granite, forming a headland, or peninsula.

Headlands and bays are formed when there are parallel sections of softer and harder rock perpendicular to the coast. The sea erodes the softer rock faster than the harder rock, forming a bay. The harder rock that is left protruding into the sea is the headland.



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