Coastal Depositional Landforms: Beaches, Dunes, Bars, Barriers, Spits
Geography › Geomorphic Processes and Landform Evolution · Topic 3.26
Where waves lose energy and sediment is abundant, the coast builds up. Coastal depositional landforms include beaches, dunes behind the beaches, offshore bars, barrier islands, spits, tombolos and lagoons. Material is moved along the shore by longshore drift, where waves approach at an angle and carry sand in a zigzag path along the coast. Spits and bars built by this drift can close off bays and form lagoons, such as Chilika in Odisha, the largest coastal lagoon in India.
6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Beach Sand or pebbles along the shore
- Spit Ridge attached at one end
- Bar and barrier Offshore ridge or island
- Lagoon Water behind a bar
- Driving process Longshore drift
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic completes the study of coastal landforms with the features built by waves and currents. It ends the group on the landforms made by each agent, and the macro then moves to the landforms of the world, such as mountains and plateaus. Previous topic: Coastal Erosional Landforms: Cliffs, Terraces, Caves, Stacks. Next topic: Landforms of the World: Fold Mountains, Block Mountains, Volcanic Mountains.
What Are the Depositional Landforms of Coasts?
| Landform | Description |
|---|---|
| Beach | Deposit of sand and shingle between low and high water levels |
| Longshore drift | Waves arriving obliquely move sediment along the shore in a zig-zag, shifting material in one direction |
| Spit | A ridge of sand or shingle attached to land at one end and extending into open water, as where the coast changes direction |
| Bar and barrier island | A ridge across a bay mouth; if it seals the bay it forms a lagoon; barrier islands lie parallel to the coast |
| Tombolo | A bar that links an island to the mainland |
| Lagoon | Shallow water body separated from the sea by a bar or spit |
| Sand dunes | Wind-blown sand piled behind beaches |
India has famous lagoons: Chilika in Odisha, the largest brackish water lagoon in Asia and a Ramsar site; Pulicat on the border of Andhra Pradesh and Tamil Nadu; and the backwaters (kayals) of Keralam (Kerala), such as Vembanad, which are shore lagoons connected by canals.
How Does Longshore Drift Work?
Waves usually reach the shore at an angle. The swash (uprush) carries sand up the beach at that angle, and the backwash (return) pulls it straight down the slope under gravity. The grains therefore move in a zigzag path along the coast. The net movement is called longshore or littoral drift, and it can move large amounts of sand each year. Where the coast bends sharply or a river mouth lies ahead, the sand goes on in the old direction and builds a spit into the water. Man-made structures like groynes and breakwaters trap sand on one side and starve the coast on the other, which is why many ports need dredging.
What Are the Main Depositional Landforms?
| Landform | Description | Examples |
|---|---|---|
| Beach | Gently sloping accumulation of sand, shingle or pebbles between low tide and the highest wave reach | Marina (Chennai), Puri, Kovalam, Copacabana |
| Coastal dune | Wind-blown sand ridges behind the beach, often anchored by plants | Odisha and Tamil Nadu coasts |
| Offshore bar | Submerged or partly exposed ridge of sand parallel to the coast | Gulf coasts |
| Barrier island (barrier beach) | Long sandy island parallel to the coast, separated from the mainland by a lagoon | Outer Banks (USA) |
| Spit | Ridge of sand or shingle attached to the land at one end and ending in the sea; a hooked end is a recurved spit | Sandy Hook (USA); spits on the Odisha coast |
| Tombolo | Bar connecting an island to the mainland | Chesil Beach (England) |
| Lagoon | Shallow water body cut off from the sea by a bar or spit | Chilika (Odisha), Pulicat (Andhra Pradesh and Tamil Nadu), Vembanad (Kerala) |
What Are Emergent and Submergent Coasts?
The shape of a coast also depends on changes in the relative level of land and sea. Submergent coasts form when the land sinks or the sea level rises, drowning river valleys and glacial valleys. A ria is a drowned river valley, with a branching, irregular shape, as in southwest Ireland, Sydney Harbour and the Konkan coast, and a fjord is a deep, steep-sided drowned glacial valley, as in Norway, Chile, Greenland and New Zealand. A Dalmatian coast, as in Croatia, has islands parallel to the coast formed from drowned mountain ridges. Emergent coasts form when the land rises or the sea falls, leaving raised beaches, marine terraces and old cliffs above the present sea level, as along parts of the Tamil Nadu and Gujarat coasts. India’s coast is mainly smooth and has few indentations, apart from places such as the Gulf of Khambhat, as in Coastal Plains, Coral Reefs and Islands of India (Andaman and Nicobar Islands, Lakshadweep).
Why Do These Features Matter?
- Tourism and fishing: beaches and lagoons support tourism and fisheries, such as the rich fisheries of Chilika.
- Protection: dunes, bars and barrier islands absorb wave energy and storm surge, so protecting them reduces cyclone damage.
- Biodiversity: lagoons shelter migratory birds. Chilika is a Ramsar site and a winter home to large flocks of birds.
- Shifting sands: spits and bars move, silt up harbours and mouths of lagoons, and require dredging.
The erosional side of the coast is in Coastal Erosional Landforms: Cliffs, Terraces, Caves, Stacks. As an analytical point, a coast is a balance between erosion and deposition; dams on rivers that cut off the supply of sand, and sand mining on beaches, tip that balance towards erosion and shrink the beaches that protect the shore.
Why Is This Topic Important?
- Terms Spit and bar are asked
- India Chilika, Pulicat, Vembanad
- Protection Dunes and barriers
What Came Next?
The next topic describes the mountains of the world: fold, block and volcanic mountains. Next topic: Landforms of the World: Fold Mountains, Block Mountains, Volcanic Mountains.
Key People and Terms
- Longshore drift Zigzag sand movement along the coast
- Spit Ridge joined to land at one end
- Tombolo Bar linking island and mainland
- Barrier island Sandy island parallel to coast
- Lagoon Water body behind a bar
- Swash Uprush of a wave
Exam Corner
Points to Remember
- Chilika is the largest coastal lagoon in India.
- A spit is attached at one end.
- A tombolo joins an island to the mainland.
- Longshore drift moves sand in a zigzag.
- Lagoons form behind bars.
Do Not Confuse With
- Spit and bar Attached at one end versus attached at both or free
- Lagoon and lake Coastal water behind a bar versus inland
- Swash and backwash Uprush at an angle versus return straight down
Memory Hook
Swash slants, backwash drops; spit grows, lagoon stops.
Mains Angle
Questions ask about lagoons and sand movement. These points add depth.
- Process Longshore drift
- Forms Spit, bar, lagoon
- Risks Sand mining and dams
A Question You May Face
An original practice question, not a past paper question.
“Explain how spits, bars and lagoons are formed and discuss the importance of the lagoons of India’s east coast.”
How to Answer
- Process Longshore drift.
- Forms Spit and bar.
- Lagoons Chilika and Pulicat.
- Threats Silting, pollution.
GS Relevance
Frequently Asked Questions
What is longshore drift?
Longshore drift is the movement of sand and shingle along a coast. Waves arrive at an angle and push the material up the beach in the direction of the wind, and the backwash carries it straight back down, so the sediment moves in a zig-zag along the shore.
What is the difference between a ria and a fjord?
A ria is a drowned river valley, with a branching irregular shape that deepens toward the sea, as in southwest Ireland. A fjord is a drowned glacial valley, deep and steep-sided, as in Norway and New Zealand. Both result from submergence of the coast.
Which is the largest lagoon in India?
Chilika Lake in Odisha is the largest brackish water lagoon in India and in Asia. It is separated from the Bay of Bengal by a sandbar, and is a Ramsar wetland that supports migratory birds and fisheries and the Irrawaddy dolphin.
What is longshore drift?
Longshore drift is the movement of sand and shingle along a beach in a zigzag path. Waves approach at an angle and carry grains up the beach in the swash, while the backwash pulls them straight down, so the net movement is along the coast. It builds spits and bars.
What is a tombolo?
A tombolo is a bar of sand or shingle that connects an island or sea stack to the mainland or to another island. It forms where waves bend around an island and lose energy, so sediment is deposited in the sheltered water behind it. Chesil Beach in England is an example.
PYQ Practice — Statement Analysis
1 Chilika is a lagoon in Odisha.
It is the largest brackish lagoon in Asia.
2 Constructive waves erode and remove beach material.
Destructive waves do; constructive waves build beaches.
3 A spit is attached to the land at one end.
A bar may be joined at both.
4 Longshore drift moves sand straight up and down the beach.
It moves sand in a zigzag along the coast.
Past Mains Questions on This Topic
This topic comes under Geomorphic Processes and Landform Evolution. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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