Coastal Morphology Group • Scripps Institution of Oceanography
BackCliffs and Platforms
ithout a beach, wave energy erodes the bedrock of the inner shelf and forms platforms and sea cliffs. A notch is cut in cliff material near mean sea level. Abrasion, notching, and structural failure of the cliff lead to retreat.
Close view of features at the base of a sea cliff. Doug Inman inspects a wave-cut notch in the sandstone sea cliff at Solana Beach.Photographer - Pat Masters, image used with permission. Rollover the photo to see extent of individual features.
Broad view of exposed cliff, platform, and beach.Photographer - Pat Masters, image used with permission. Rollover the photo to see extent of individual features.
The platform is the flat, gently-sloping erosional surface extending seaward from the sea cliff and notch. The platform results from wave abrasion in the surf zone and provides the resistant surface supporting the mobile sediments of the beach
This platform was cut during the present near stillstand in sea level that has persisted since about 6,000 years ago. Sea level is rising now about 20 cm per century along the southern California coast.
The sea cliff is the landward feature remaining as waves cut into mountainous coasts. This type of collision coast characterizes the entire Pacific rim of the Americas as well as California.
Sea cliff retreat releases fine sediment, sand, and cobbles to the littoral zone as slumps and rubble. Fine sediment is carried offshore to deeper water while sand and cobbles are worked along the beach by waves and longshore currents. The cobbles remain after winter storms and increase wave abrasion of the platform in the surf zone. Under natural conditions, sea cliffs are thought to contribute about 10-20% of the sand to the beaches of the Oceanside Littoral Cell with the rest coming from streams and bluffland erosion.
Long-term rates of cliff retreat at Solana Beach in the Oceanside Littoral Cell are estimated at 6-11 cm/yr (or m/100 yr). Along some other parts of the California coast, sea cliffs are retreating much faster at a meter or more per year. Cliff failure is accelerated by development and irrigation runoff from the cliff top.
This platform was cut during the present near stillstand in sea level that has persisted since about 6,000 years ago. Sea level is rising now about 20 cm per century along the southern California coast.
The sea cliff is the landward feature remaining as waves cut into mountainous coasts. This type of collision coast characterizes the entire Pacific rim of the Americas as well as California.
Sea cliff retreat releases fine sediment, sand, and cobbles to the littoral zone as slumps and rubble. Fine sediment is carried offshore to deeper water while sand and cobbles are worked along the beach by waves and longshore currents. The cobbles remain after winter storms and increase wave abrasion of the platform in the surf zone. Under natural conditions, sea cliffs are thought to contribute about 10-20% of the sand to the beaches of the Oceanside Littoral Cell with the rest coming from streams and bluffland erosion.
Long-term rates of cliff retreat at Solana Beach in the Oceanside Littoral Cell are estimated at 6-11 cm/yr (or m/100 yr). Along some other parts of the California coast, sea cliffs are retreating much faster at a meter or more per year. Cliff failure is accelerated by development and irrigation runoff from the cliff top.
Coastal Morphology Group • Scripps Institution of Oceanography
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Last modifed Friday, June 25, 2003