A wave-cut platform is a distinctive geological feature found along coastlines, appearing as a relatively flat, rocky surface extending seaward from the base of a cliff. These platforms are typically exposed at low tide, revealing a broad, often rugged, expanse of rock. Their formation is a continuous process driven by the powerful and relentless action of ocean waves against the land.
The Forces at Play
Ocean waves exert significant physical forces that shape coastal landscapes. Hydraulic action occurs as waves crash against cliffs, forcing water and compressed air into cracks and crevices within the rock. The sudden release of pressure as the wave recedes can cause the rock to weaken and fracture, dislodging fragments.
Abrasion is another significant erosional process, where sediment and rock particles carried by waves are hurled against the cliff face. These abrasive materials act like sandpaper, wearing down the rock.
Attrition describes the process where rock fragments carried by waves collide with each other. These impacts cause the fragments to break down into smaller, smoother, and more rounded pieces. Attrition also contributes to the erosional power of waves by providing more effective abrasive tools.
Stages of Formation
The formation of a wave-cut platform begins with the relentless attack of waves at the base of a cliff, concentrated around the high-tide mark. This persistent wave action gradually erodes a concave indentation into the rock, known as a wave-cut notch.
As the wave-cut notch expands inwards, it progressively undermines the stability of the cliff face above it. Eventually, the weakened rock can no longer support the weight of the overlying material, leading to a collapse of the unsupported cliff section. This process causes the cliff to retreat inland, leaving behind a new, exposed rock face.
The debris from the collapsed cliff is then transported away by wave action. As the cliff continues its cycle of notching and collapsing, the flat, gently sloping surface left behind at the base, at or just below sea level, becomes the developing wave-cut platform.
What Influences Their Development
The rate and extent of wave-cut platform development are significantly influenced by the type of rock forming the coastline. Softer, less resistant rocks, such as shale or sandstone, erode more quickly due to their weaker mineral bonds and structural integrity. Conversely, harder, more resistant rocks like granite or basalt erode at a much slower pace, leading to less pronounced or slower-forming platforms.
Wave energy and exposure also play a crucial role in shaping these features. Coastlines directly exposed to powerful ocean waves, often characterized by strong prevailing winds and long fetches, experience higher rates of erosion. These high-energy environments accelerate platform development compared to more sheltered bays or inlets.
Fluctuations in sea level over geological timescales can impact the elevation and preservation of wave-cut platforms. A stable sea level allows for continuous erosion at a consistent elevation, promoting platform development. However, significant drops in sea level can expose previously submerged platforms, while rises can submerge older platforms, leaving them as submerged terraces.
Observing Wave-Cut Platforms
The surface of these platforms often contains various depressions and crevices. These depressions frequently retain seawater even at low tide, forming rock pools that harbor diverse marine life.
Additionally, isolated rock formations known as stacks or stumps may remain on the platform as remnants of the original cliff face, resisting erosion more effectively. Wave-cut platforms provide tangible evidence of long-term coastal erosion and the dynamic interplay between land and sea.