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Concept
Wave pounding
Résumé
Wave pounding is the 'sledge hammer' effect of tonnes of water crashing against cliffs. It shakes and weakens the rocks leaving them open to attack from hydraulic action and abrasion. Eroded material gets carried away by the wave. Wave pounding is particularly fierce in a storm, where the waves are exceptionally large, and have a lot of energy. It is an important engineering consideration in the construction of structures such as seawalls and dams.
Wave pounding is a force of erosion along coast lines. The effects of wave pounding are influenced by wave shape, ocean chemistry, rock type, and morphology of the coastal landscape. There are three different types of waves to consider in this process: spilling, plunging, and surging waves. Spilling waves have the least amount of energy associated with them due to their shallow ocean floor. Plunging and surging waves contain the energy associated with wave pounding. Plunging and surging waves occur on moderate to steep angled beach plains.
Along with energy, the water chemistry will also affect the rock exposed to the erosion. Salt, calcium, and acid levels in the ocean have adverse effects on specific rock types. The chemical weathering due to wave processes is part of why wave pounding is so damaging. Wave pounding is not primarily caused by tectonic margins. Wave pounding will occur any place around the world as long as the angle of the beach plain is steep enough to generate the plunging and surging waves. The action of wave pounding is the kinetic energy delivered by waves fracturing or removing rock and or sand from land sea margins. Any solid material not fully removed by this action will be hydraulically fractured as well. The surging water fills the existing cracks and physically wedges the rock apart. One specific rock is particularly susceptible to the hydraulic action.
Chert rock, or any other rock which has fractured and has had siliceous material fill in the cracks, seems to be very weak to wave action. The water can get into the bubbles and voids in the quartz fracture lines.
Source officielle
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