Erosional Landforms in Coastal Geomorphology

Imagine standing at the edge of a rugged coastline, where towering cliffs, isolated rock columns, and deep caves dominate the scenery. These spectacular landforms are not crafted overnight; they are the result of millions of years of constant battle between the sea and land. Waves, driven by powerful winds, relentlessly erode the coastline, giving birth to unique landforms called erosional landforms. Let’s explore these fascinating structures in detail.

1. Sea Cliffs

Picture This: You are standing at the edge of a vertical rocky wall overlooking the ocean — that’s a sea cliff. These steep, often vertical, rock walls rise almost directly from the sea, formed by the relentless pounding of waves.

How Are Sea Cliffs Formed?

• Marine Erosion at the Base: Continuous waves strike the base of the rock, wearing it away (marine erosion).
• Sub-Aerial Weathering at the Top: Wind, rain, and other weathering agents gradually weaken the upper parts of the cliff.
• The Result: If erosion at the base is much faster than at the top, an overhanging cliff with a steep vertical face is formed. If weathering at the top dominates, the cliff becomes less steep and loses its sharp vertical character.

What Influences Their Shape?

• Rock Type:
  • Resistant Rocks (like sandstone or limestone): Form sharp, steep cliffs.
  • Weak Rocks (like clay or shale): Form less steep, crumbling cliffs.
• Balance of Erosion:
  • If marine erosion is dominant → steep vertical cliffs.
  • If sub-aerial weathering dominates → gradual sloping cliffs.

Types of Cliffs (As Classified by A. Guilcher)

2. Capes and Bays

Imagine This: While walking along the coast, you suddenly notice a landmass jutting out into the sea (Cape) and next to it, a curved inlet where the water penetrates inland (Bay). These contrasting features are formed due to differential erosion — when hard and soft rocks erode at different rates.

How Are They Formed?

• Capes (Headlands):
  • Made of resistant rocks (like sandstone or limestone).
  • Erode slowly, leaving the land jutting out into the sea.
  • Example: Kanyakumari in India.
• Bays:
  • Formed where soft rocks (like clay or shale) erode quickly.
  • This forms a wide, semi-circular inlet where the sea moves inland.
  • Example: Mumbai Bay.

3. Wave-Cut Cliffs and Wave-Cut Terraces

Imagine This: Over thousands of years, as waves keep eroding a cliff, it begins to retreat inland. What it leaves behind is a flat, rocky platform called a wave-cut terrace.

How It Happens?

• Waves constantly erode the cliff base.
• Over time, the cliff recedes, leaving behind a flat rocky platform covered with debris — wave-cut terrace.
• This terrace remains exposed during low tide and submerged during high tide.

Wave-Cut Cliff vs. Wave-Cut Terrace

4. Sea Caves, Sea Stacks, and Sea Stumps

Sea Caves:

• Imagine This: The continuous lashing of waves against a cliff creates hollows in the rock.
• Over time, these hollows enlarge into sea caves.
• Example: Elephanta Caves in Maharashtra.

Sea Stacks:

• If the roof of a sea cave collapses, leaving a portion of the cliff isolated, it forms a sea stack — a tall, vertical rock pillar standing in the sea.
• Example: Vivekananda Rock in Kanyakumari.

Sea Stumps:

• As sea stacks continue to erode, they shorten and reduce to small rocky outcrops just visible above the sea surface, called sea stumps.

5. Gloups and Geos

Gloups (Blowholes):

• Imagine waves forcing water into a sea cave.
• When compressed air gets trapped, it bursts out forcefully through a hole in the cave roof — creating a vertical shaft or gloup.
• During high tides or storms, water spurts out of gloups like a natural fountain.

Geos (Narrow Inlets):

• If the roof of a cave completely collapses, it forms a long, narrow inlet or creek along the coastline, called a geo.
• Example: Sea inlets along the Konkan coast.

6. Coves

• Imagine This: You are exploring a coastline and stumble upon a small, secluded, semi-circular bay surrounded by cliffs — that’s a cove.
• Coves are formed where soft rocks (like clay) are sandwiched between hard rocks (like limestone).
• Continuous erosion removes the soft rocks, creating elliptical-shaped inlets known as coves.
• Example: Lulworth Cove in the UK.

✅ Why Are These Landforms Important?

• Economic Value: Many sea caves, cliffs, and bays attract tourists, boosting the local economy.
• Coastal Defense: Cliffs act as natural barriers against storm surges and high tides.
• Biodiversity Hotspot: Coastal landforms harbor rich marine biodiversity, supporting fisheries.

💡 Quick Recap

1. Cliffs are formed when waves erode coastal rocks vertically.
2. Continuous erosion forms caves, and if the roof collapses, it leads to stacks and eventually stumps.
3. Hard rocks form capes, while soft rocks create bays.
4. Receding cliffs leave behind flat rocky platforms called wave-cut terraces.
5. Forceful water bursting through a cave roof creates gloups, while collapsed caves create long narrow inlets called geos.
6. Where alternating hard and soft rocks exist, coves are formed.

💎 Fun Fact:

Did you know that the famous “Twelve Apostles” along Australia’s Great Ocean Road are actually Sea Stacks? They were once part of a cliff but relentless wave action sculpted them into towering rock pillars.🌊🪨