Lecture on Cliff Retreat and Marine Terraces

Key Concepts

• Cliff Retreat: The process by which cliffs are eroded over time by ocean waves, causing them to collapse and retreat inland.
  • Significant in coastal areas like Encinitas and San Diego where homes are built on cliff edges.
  • Ocean waves erode the base of cliffs, creating notches that lead to collapses.

Erosion Process

• Notch Formation: Waves cut into the base of the cliff, forming a notch.
• Cliff Collapse: When the notch becomes large enough, the cliff above collapses.
• Wave Cut Platforms: These are horizontal areas at the base of cliffs formed by wave erosion.
• Marine Terraces: Elevated wave cut platforms, formed as land uplifts over geological timescales.

Examples

• Wave Cut Bench and Marine Terraces: Visible at low tide, illustrating historical erosion.
• Geological Timelines: Marine terraces form over hundreds of thousands of years.
• Occam's Razor: The simplest explanation (land uplift and wave erosion) is preferred for the formation of marine terraces.

San Clemente Island Example

• Multiple marine terraces visible, representing historical wave cut platforms.
• Stair-Step Formation: Indicative of gradual land uplift and varying sea levels over time.

Mount Soledad Example

• Local Illustration: Displaying current marine terraces with homes built on them.
• Geological Uplift: Active faults like Rose Canyon contribute to local uplifts.

Sea Level Changes

• Interglacial and Glacial Periods: Sea levels fluctuate due to ice volume changes.
• Graph Interpretation:
  • Historical sea level changes shown over half a million years.
  • Current sea level is high due to lower global ice volumes.
• Sawtooth Pattern: Characteristic pattern of sea level rise and fall over geological timescales.

Implications

• Property Risks: Homes built on marine terraces or cliff edges risk collapse.
• Future Considerations: Continuous sea level rise expected as global ice decreases.

Summary

• Understanding of cliff retreat and marine terraces is essential for coastal planning and risk management.
• Geological observations and simple explanations (e.g., Occam’s Razor) help interpret long-term coastal changes.