Coastline of Submergence and Emergence

The Earth’s coastlines are dynamic and often undergo vertical changes due to fluctuations in sea level, tectonic movements, or isostatic adjustments. Based on whether the land is sinking (submerging) or rising (emerging) relative to sea level, coastlines are classified into:

Coastline of Submergence

A submergent coastline is formed when land sinks or sea level rises, causing previously dry land or river valleys to be inundated by the sea.

Key Characteristics:

• Drowned river valleys and glacial troughs
• Highly irregular and indented coastline
• Numerous inlets, bays, and estuaries
• Common in areas experiencing post-glacial sea level rise or tectonic subsidence

a. Ria Coasts

• Ria = Drowned River valley.
• Formed when the lower part of a river valley is submerged due to rise in sea level.
• Appears as a deep, narrow inlet with a funnel-shaped mouth.
• Coastline is irregular with many branches and inlets.
• Example: Coast of south-west Ireland, parts of Spain (Galicia).

b. Fiord (Fjord) Coasts

• Fiords are drowned glacial valleys.
• Formed when glacial troughs are flooded by the sea.
• Characterized by:
  • Steep-sided, deep, U-shaped valleys
  • Very deep water and narrow width
  • Often have hanging valleys
• Example: Norwegian coast, New Zealand, Alaska, and Chile

c. Dalmatian Coasts

• Named after the Dalmatian coast of Croatia (Adriatic Sea).
• Formed where longitudinal valleys and hills parallel to the coast are submerged.
• Features:
  • Alternating long narrow islands and inlets.
  • Coastal ridges become islands, and valleys become channels/sea arms.
• Coastline appears parallel and elongated.

Coastline of Emergence

An emergent coastline results when land rises or sea level falls, exposing parts of the continental shelf or previously submerged land.

Key Characteristics:

• New coastal landforms appear due to uplift
• Straight, less indented coastline
• Features include raised beaches, wave-cut platforms, marine terraces, and relict cliffs
• Often formed due to isostatic uplift, tectonic activity, or eustatic fall in sea level

Emergent Lowland Coasts

• Formed in gently sloping terrain where the land is uplifted.
• Characterized by:
  • Wide coastal plains
  • Raised beaches
  • Extensive mudflats
  • Coastal marshes and swamps
• Often associated with delta formation due to sediment deposition.
• Example: Eastern coast of India (e.g., Tamil Nadu and Andhra Pradesh coasts)

Emergent Upland Coasts

• Found in hilly or mountainous coastal areas.
• Characterized by:
  • Raised marine terraces
  • Relict cliffs and wave-cut benches found well above present sea level.
• Evidence of past sea levels and tectonic uplift.
• Example: Scotland, Southern California, parts of Japan

Comparison Table: Coastlines of Submergence vs Emergence