Coastlines of Emergence and Submergence
Coastlines of emergence and submergence are coastal landscapes shaped by geological and sea level changes over time. These changes are often related to tectonic activities, glacial cycles, and other natural processes.
Coastlines of Emergence
Emergent coastlines are formed when land rises relative to sea level. This can happen due to tectonic uplift, where geological processes push the land upward, or a drop in sea level, often associated with the end of an ice age when large ice sheets melt and the water redistributes.
Characteristics:
- Raised Beaches: Old beach lines that are now above current sea level, indicating a former higher sea level.
- Marine Terraces: Flat, step-like landforms created by wave action at previous sea levels, now found inland.
- Sea Cliffs: Steep faces formed by wave erosion, now situated above the current sea level.
- Wave-Cut Platforms: Flat areas at the base of sea cliffs that were formed by wave erosion and now are exposed above sea level.
Example: The west coast of Scotland features numerous raised beaches and marine terraces, indicating significant uplift over time.
Coastlines of Submergence
Submergent coastlines occur when land sinks relative to sea level, or sea level rises, submerging previously dry land. This is often due to post-glacial rebound, where land previously compressed by ice sheets sinks as the ice melts and the weight is lifted.
Characteristics:
- Rias: Drowned river valleys that form estuaries. These are typically characterized by steep sides and branching patterns.
- Fjords: Deep, glacially carved valleys that are inundated by sea water, often with steep sides and deep waters.
- Estuaries: Broad, tidal mouths of rivers where freshwater meets and mixes with seawater, often rich in nutrients and biodiversity.
- Dalmatian Coasts: Coastal areas where parallel ridges and valleys are submerged, creating a series of elongated islands and inlets.
Example: The coast of Norway is famous for its fjords, which are deep, glacially carved valleys filled with seawater.
Detailed Examples
Emergent Coastline: California’s Marine Terraces
- The coastal region of California, particularly around the Point Reyes National Seashore, showcases a series of marine terraces.
- These terraces were formed by wave action during different sea level stands and have been uplifted by tectonic forces related to the San Andreas Fault system.
Submergent Coastline: Chesapeake Bay, USA
- The Chesapeake Bay is a classic example of a ria coastline.
- Formed by the drowning of the Susquehanna River valley, the bay has numerous tributaries that resemble the branches of a tree, creating a highly indented coastline.
- This region was significantly affected by post-glacial sea level rise, resulting in the current drowned valley system.
Formation Processes
Emergence:
- Tectonic Uplift: Movement of tectonic plates can push coastal areas upwards.
- Isostatic Rebound: The rise of land following the melting of ice sheets, as seen in parts of Canada and Scandinavia.
Submergence:
- Sea Level Rise: Global warming and the melting of ice caps contribute to rising sea levels.
- Subsidence: The gradual sinking of land, which can be due to natural processes or human activities such as groundwater extraction.
Significance
Understanding these coastlines helps in studying past climate changes, predicting future coastal dynamics, managing coastal resources, and mitigating natural hazards. For instance:
- Climate Change Impact: Coastal submergence due to rising sea levels poses significant risks to coastal communities worldwide.
- Biodiversity: Submergent coastlines often support rich ecosystems due to their complex physical environments.
- Cultural and Historical Insights: Raised beaches and marine terraces provide clues to ancient human settlements and sea level changes.
In conclusion, coastlines of emergence and submergence provide crucial insights into geological processes and environmental changes, shaping the way we understand and interact with coastal regions.
