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Difficulty: HardOceans, Coastal Processes, and Coastal Landforms

When swash carries beach material up a shoreline at an oblique angle and backwash drags it perpendicular to the coast, sediment migrates laterally via longshore drift. If this ongoing deposition extends an embankment entirely across the entrance of an indentation, connecting two headlands and impounding a coastal lagoon behind it, which geomorphic feature is formed?

  1. A baymouth barAnswer
  2. B
    An oxbow lake
  3. C
    A scree slope
  4. D
    A metamorphic slate bench

Answer

A baymouth bar
Longshore drift moves sediment along the shoreline when waves break obliquely. When sand and shingle build out across an indentation or bay until reaching the opposite headland, the feature completely encloses the bay to form a baymouth bar, isolating a lagoon behind it.

Step-by-Step Solution

1
Analyze the marine sediment transport mechanism described in the stem
Identify that oblique swash and direct backwash produce longshore drift along the coast
Prevailing wind direction governs swash angle while gravity dictates backwash return
2
Determine the morphological outcome of longshore drift across a bay
Sediment builds a spit that progressively extends across the bay mouth to the opposing headland
Uninterrupted deposition joins both sides and traps water behind the sand ridge
3
Match the complete closure feature to coastal landform terminology
A continuous ridge sealing off a bay and forming a lagoon is classified as a baymouth bar
Distinguishes a fully closed bar from an open-ended spit or offshore bar

Key Concept

Longshore drift and coastal depositional landforms (Baymouth bar formation)
Estimated Time:1m 30s
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Topics

Oceans, Coastal Processes, and Coastal Landforms

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