Chapter 10 G.C. Leong’s  Certificate Physical and Human Geography

Chapter 10: Coastal Landforms

This chapter examines the boundary between land and sea. The coast is a high-energy zone where waves are the primary agent of change, constantly carving out new features (erosion) and building up others (deposition).

1. The Mechanism of Marine Erosion

Waves act like a “hammer” against the shoreline through four main processes:

• Corrasion (Abrasion): Waves fling pebbles, sand, and boulders against the base of cliffs, wearing them away.
• Hydraulic Action: As waves hit a cliff, they trap air in cracks. The pressure of this compressed air shatters the rock.
• Attrition: The rocks being carried by the waves strike each other, breaking down into smaller, rounded pebbles and sand.
• Corrosion (Solution): The chemical action of seawater, especially on limestone or chalk coasts, dissolves the minerals.

2. Coastal Erosional Landforms

• Cliffs and Wave-cut Platforms: Waves undercut the base of a cliff to form a “notch.” Eventually, the overhanging rock collapses, and the cliff retreats, leaving a flat Wave-cut Platform at the base.
• Bays and Headlands: On “discordant” coasts (where hard and soft rocks run perpendicular to the sea), the soft rocks erode faster to form Bays, while the harder rocks stick out as Headlands.
• Caves, Arches, Stacks, and Stumps:
  1. A hole is eroded into a headland to form a Cave.
  2. When two caves meet from opposite sides, an Arch is formed.
  3. When the arch collapses, a pillar of rock called a Stack remains.
  4. When the stack is eroded down to a nub, it is called a Stump.

3. Coastal Depositional Landforms

• Beaches: Temporary accumulations of sand, gravel, or pebbles between the low and high water marks.
• Spits and Bars:
  • Spit: A narrow ridge of sand attached to the land at one end and heading out into the sea (e.g., Chesil Beach).
  • Bar: When a spit grows long enough to connect two headlands, sealing off a lagoon.
• Marine Dunes and Machair: Wind blows sand from the beach inland to form dunes, which are often stabilized by Marram Grass.

4. Types of Coasts

Coasts are classified based on whether the land has risen or the sea level has changed:

• Coastlines of Submergence: Formed when the sea level rises or the land sinks.
  • Rias: Submerged river valleys (V-shaped).
  • Fjords: Submerged glacial valleys (U-shaped with steep walls).
  • Dalmatian Coast: Formed when mountains run parallel to the coast and are partially submerged, creating a chain of islands.
• Coastlines of Emergence: Formed by the uplift of land or a fall in sea level.
  • Uplifted Lowland Coast: Flat, smooth coastlines with lagoons.
  • Emergent Upland Coast: Characterized by “Raised Beaches” and “Abandoned Cliffs” found well above the current sea level.

Revision Questions & Answers

Q1: What is the difference between a Ria and a Fjord?

• A: A Ria is a submerged river valley (found in regions like Southwest Ireland), characterized by a funnel shape and V-shaped profile. A Fjord is a submerged glacial valley (found in Norway/Chile), characterized by very deep water and steep, U-shaped side walls.

Q2: How does “Longshore Drift” work?

• A: It is the movement of sediment along the coast in a zigzag manner. Waves (the swash) push material up the beach at an angle, while the backwash pulls it straight down the slope due to gravity.

Q3: Which part of a cliff is most vulnerable to erosion and why?

• A: The base of the cliff. This is where hydraulic action and corrasion are most intense, as waves have the most energy and carry the most “tools” (stones/sand) at the water line.

Q4: What is a Tombolo?

• A: A Tombolo is a special type of spit or bar that connects an island to the mainland (e.g., the Rock of Gibraltar was once a tombolo).

Quick Summary Table: The Arch-to-Stump Cycle