1. Past Sea Level Changes:
* Higher sea levels: Elevated marine terraces demonstrate that the sea level was once higher than it is today. The terraces themselves represent former shorelines that have been uplifted or emerged due to tectonic activity or changes in global sea level.
* Magnitude of change: The elevation difference between the terraces and the present sea level indicates the magnitude of the sea level change.
* Timing: The terraces can be dated using various methods, giving us a timeline of past sea level fluctuations.
2. Uplift or Subsidence:
* Uplift: If a coast is experiencing tectonic uplift, the former shorelines are lifted above the present sea level, forming terraces.
* Subsidence: While less common, if a coast is subsiding, the sea level appears to rise relative to the land, and terraces may form below the present sea level.
3. Erosion and Deposition:
* Wave action: The formation of terraces involves the erosion of the coastline by waves, creating a platform. As the sea level drops or the land rises, the platform becomes an elevated terrace.
* Deposition: Sediment deposition can also contribute to terrace formation. As sea level drops, sediment accumulates on the former shoreline, creating a shelf that is later uplifted.
4. Climate Change and Isostatic Adjustments:
* Glacial-interglacial cycles: Marine terraces can provide valuable data about past glacial and interglacial cycles. During periods of glacial expansion, water is locked up in ice sheets, causing sea level to drop. When glaciers melt, sea level rises again.
* Isostatic rebound: After glacial periods, the Earth's crust rebounds (rises) due to the removal of the weight of the ice. This isostatic rebound can also contribute to the elevation of marine terraces.
In summary, elevated marine terraces provide a rich record of past sea level changes, tectonic activity, erosion, deposition, and climate change. They are a valuable tool for understanding the dynamic history of our coastlines.
