Emergent and Submergent Coasts
Another important factor in understanding shorelines is tectonic activity and the rise and fall of sea level.
Submergent coastlines display characteristics caused when sea level rises or the land sinks down. Submergent coastlines:
* Contain estuaries and barrier bars, and barrier island systems.
* Ridges that separate valleys that propel into the sea.
Example: East Coast (see Figure 12.4).
Emergent coastlines display characteristics caused when sea level drops or the land rises (from tectonic uplift).
* Wave cut platforms and elevated marine terraces.
Example: West Coast California (Figure 12.26).
Figure 12.26. San Diego's coastline displays characteristics of both emergent and submergent coastlines, having both seacliffs, headlands and marine terraces (emergent), and bays and estuaries filling flooded river valleys (submergent). View south along the Coast Highway at Torrey Pines Nature Preserve.
In some regions around the world, tectonic forces are pushing rocks up along coastal regions, mostly in regions associated with active continental margins. There areas are called emergent coasts and display features including sea cliffs and marine terraces (see below). Where sea level is rising faster than land is rising, or where coastal areas are sinking, it is called a submergent coast. Submergent coasts are associated with passive continental margins with wide coastal plains and continental shelves. Estuaries are associated with submergent coastlines formed when sea level rises and floods existing river valleys. Active margins can have both emergent and submergent coastlines in close proximity to each other.