& PARALLEL DUNES
& KEYED-UP SPIT
SRIHARIKOTA BAR
Coastal Depositional Landforms
Sand & Shingle Beaches · Parallel Coastal Dunes · Off-Shore Bars, Barrier Bars & Spits · Lagoons & Indian Exemplars (28 Micro-Realms)
From Temporary Beaches to Barrier Lagoons & Coastal Plains (NCERT Chapter 7)
Most of the sediment making up coastal landforms comes from land carried by rivers and streams or from wave erosion. Beaches are temporary features—composed of quartz sand or small pebbles and cobbles (Shingle Beaches)—backed by parallel ridges of wind-winnowed Coastal Dunes. Seaward of the low-tide waterline, waves build a submerged Off-Shore Bar; when exposed above water by further sand addition, it becomes a Barrier Bar. When keyed up to a headland or bay end, it forms a Spit, enclosing a Lagoon that gradually fills with sediment to become a broad Coastal Plain.
I. Beaches (Sand vs. Shingle) & Parallel Coastal Dunes (NCERT Core)
Beaches Are Temporary!
- Characteristic of deposition-dominated shores
- Sediment comes from rivers or wave erosion
- Beaches are TEMPORARY features (NCERT)!
Beach Profile Anatomy
- Backshore: Dry storm terrace (Berm)
- Foreshore: Intertidal swash-backwash ramp
- Nearshore: Breaker zone & longshore bars
Summer vs. Winter Beach
WIDE BERM
OFFSHORE BAR
- Gentle summer swells push sand onshore
- High-energy monsoon/winter storms strip sand
- Into submerged offshore bars (NCERT)
Shingle Beaches (NCERT)
- Most beaches are made of durable quartz sand
- Beaches containing excessively small
- Pebbles & cobbles = Shingle Beaches!
Pocket (Bay-Head) Beaches
- Occur as small crescentic patches
- Along rugged rocky shores between headlands
- Gokarna (Om Beach) & Palolem (Goa)
Beach Cusps & Runnels
- Rhythmic crescentic horns & embayments
- Coarse shingle on horns; fine sand in bays
- Formed by edge-wave swash sorting
Parallel Coastal Dunes
- Just behind the beach, onshore winds
- Lift & winnow dry sand from beach surface
- Forms long ridges PARALLEL to coast (NCERT)
II. Off-Shore Bars, Barrier Bars, Spits & Tombolos (NCERT Core)
1. Off-Shore Bar (NCERT)
- Ridge of sand & shingle formed in the sea
- In the off-shore zone (seaward of low-tide)
- Lying approximately parallel to coast
2. Barrier Bar (Exposed)
- An off-shore bar which gets EXPOSED
- Above water due to further addition of sand
- Is termed a Barrier Bar (NCERT High-Yield)!
3. Spits (Keyed to Headland)
- Off-shore bars & barrier bars get keyed up
- Attached to one end of a bay or headland
- Projecting into sea = Spit (NCERT)
Recurved / Hooked Spits
- Distal free end of spit bends landward
- By wave refraction & cross-currents
- Forms a Hook or Compound Recurve Spit
Baymouth Bars
- Spit grows completely across a bay mouth
- Seals off bay from the open ocean
- Converts indentation into a closed lagoon
Tombolos (Island Tie-Bars)
- Wave refraction behind an offshore island
- Builds a sand/shingle bar connecting
- Island to mainland = Tombolo (Chesil Beach)
Cuspate Forelands
- Two spits converge from opposite directions
- Or prograde outward as triangular cape
- Dungeness (UK) & Cape Canaveral (USA)
III. Barrier Buffers, Lagoons, Tidal Marshes & Coastal Plain Succession (NCERT)
Natural Storm-Wave Buffers
- Bars, spits & lagoons are first line of defense
- Absorb destructive force of storm waves
- And tsunamis before hitting mainland (NCERT)
Lagoons (Enclosed Bays)
- Barrier bar/spit encloses a coastal bay
- Leaves only a narrow tidal inlet opening
- Bay develops into a calm Lagoon (NCERT)
Flood vs. Ebb Tidal Deltas
- Tides rush in & out of narrow barrier inlet
- Flood Tidal Delta: Builds inside lagoon
- Ebb Tidal Delta: Builds seaward of inlet
Tidal Mudflats & Creeks
- Sheltered quiet water behind barrier bars
- Allows fine river silt & clay to settle
- Kori Creek & Sir Creek (Rann of Kutch)
Salt Marshes & Mangroves
- Pneumatophore roots trap suspended mud
- Accelerates vertical accretion of lagoons
- Sundarbans, Bhitarkanika & Pichavaram
Lagoon → Coastal Plain
- Lagoon fills up with sediments from land
- Or wind-blown sand from the beach itself
- Broad Coastal Plain replaces lagoon (NCERT)!
Washover Fans & Cheniers
- Storm surges breach barrier dune crests
- Spreads lobate Washover Fans into lagoon
- Chenier: Stranded shell/sand ridge on mudplain
IV. Indian Coastal Depositional Landforms, Lagoons & Placer Sands
Marina & Chandipur Beaches
- Marina Beach: India's longest urban beach (updrift of Cooum/harbour)
- Chandipur (Odisha): Sea recedes 5 km at low tide!
- Puri, Guhagar, Calangute & Radhanagar
Chilika Lagoon (Odisha)
- India's & Asia's largest brackish lagoon
- Enclosed by 60-km long Rajhansa barrier spit
- Fed by Daya & Bhargavi (Mahanadi delta)
Pulicat & Sriharikota Bar
- India's 2nd largest brackish water lagoon
- Separated from Bay of Bengal by
- Sriharikota — a spindle-shaped Barrier Island!
Kerala Kayals & Hope Spit
KAYAL
HOPE SPIT
- Kayals: Malabar barrier backwaters (Vembanad, Ashtamudi)
- Hope Island (AP): 16-km Godavari hooked spit sheltering Kakinada port!
Ram Setu & Indian Tombolos
- Adam's Bridge (Ram Setu): 48-km chain of limestone shoals & barrier bars
- Dhanushkodi spit (Pamban) & Kurumgad Tombolo
Teri Dunes & Monazite Sands
- Teris: Iron-stained red coastal dunes in TN
- Wave winnowing concentrates heavy minerals:
- Monazite (Thorium) & Ilmenite (Kerala/Odisha)
World G to K Master Synthesis
- Completes all 5 Geomorphic Agent Realms!
- Running Water, Groundwater, Wind, Ice, Waves
- Full NCERT Chapter 7 mastery achieved
Core Distinctions
• Off-Shore Bar: Submerged ridge of sand and shingle formed in the sea in the off-shore zone (seaward of low-tide waterline) parallel to the coast.
• Barrier Bar: An off-shore bar that gets exposed above water due to further addition of sand (e.g., Sriharikota enclosing Pulicat Lake).
• Spit: An off-shore or barrier bar that gets keyed up (attached) to one end of a bay or headland while its other end projects into the sea (e.g., Kakinada Hope Island Spit).
• Tombolo: A bar/spit that connects an offshore island to the mainland.
Beaches are temporary features (built by summer swells and stripped into offshore bars by winter storms). Most beaches are made of durable quartz sand, whereas beaches containing excessively small pebbles and even cobbles are called Shingle Beaches.
3. The Lagoon → Swamp → Coastal Plain Succession (NCERT)When barrier bars and spits enclose a bay, it becomes a Lagoon (Chilika, Pulicat, Vembanad). Over time, rivers from the land and wind-blown sand from the beach fill up the lagoon into a marshy Swamp, which subsequently develops into a broad, flat Coastal Plain.
Coastal Depositional Matrix
NCERT Chapter 7 & Indian Exemplar Key