What Is a Spit? Sandy Extensions Along the Coast

A spit is a narrow finger of sand or gravel that extends from the coastline out into the sea or across a bay, formed by the process of longshore drift. When the coastline changes direction — at a river mouth, bay entrance, or headland — sediment being transported along the shore continues in its original direction, building out into open water as a spit.

Introduction

Spits are dynamic coastal features that grow, erode, and change shape in response to waves, currents, and storms. Many spits develop a curved or hooked tip where waves and currents bend the end of the spit toward the shore. Behind the spit, a sheltered area of calm water often develops into a salt marsh or lagoon, creating valuable wildlife habitat.

Definition & Key Characteristics

• Definition: A narrow, elongated ridge of sand or gravel extending from the coast into the sea
• Formation: Created by longshore drift depositing sediment where the coast changes direction
• Recurved Tip: The end of the spit often curves toward the shore due to wave refraction
• Lagoon: A sheltered body of water often forms behind the spit

Spits form where longshore drift — the movement of sediment along a coast by angled waves — encounters a change in the coastline direction. When the coast turns inland at a bay or river mouth, the sediment continues moving in its original direction, depositing material that extends as a narrow ridge into the open water. The spit grows longer as more sediment is added by continued longshore drift.

Most spits develop a recurved (hooked) tip because waves from other directions refract around the end of the spit, bending the deposited material back toward the shore. Some spits have multiple recurved hooks along their length, recording past positions of the tip before it continued growing outward.

How Spits Form

• Longshore Drift: Waves approaching the coast at an angle transport sediment along the shore
• Change in Coastline: Where the coast turns inland, sediment continues moving into open water
• Growth: Continued sediment supply extends the spit further from the coast
• Recurving: Waves from other directions bend the tip of the spit

Longshore drift is the engine of spit formation. Waves approaching the coast at an angle push sediment up the beach in the same direction as the wave (the swash), but gravity pulls the water and sediment back down the slope perpendicular to the shore (the backwash). This zigzag motion transports sediment along the coast in the prevailing wave direction.

When the coastline changes direction — at the entrance to a bay, at a river mouth, or where the coast curves inland — the sediment being transported by longshore drift continues in its original direction rather than following the coastline. This creates a ridge of sand or gravel extending from the coast into the sea, which grows longer over time as more sediment arrives.

Famous Spits

• Spurn Point, England: A 5.5 km spit at the mouth of the Humber Estuary
• Farewell Spit, New Zealand: A 26 km spit at the northern tip of the South Island
• Dungeness, England: One of the largest shingle spits in Europe
• Sandy Hook, New Jersey: A 10 km spit extending into Lower New York Bay
• Curonian Spit, Lithuania/Russia: A 98 km sand spit enclosing the Curonian Lagoon (UNESCO site)

The Curonian Spit is one of the most remarkable spits in the world, stretching 98 kilometers along the Baltic coast of Lithuania and Russia. It is only 400 meters wide in places but separates the Curonian Lagoon from the Baltic Sea. The spit features some of the tallest sand dunes in Europe, reaching 60 meters, and has been a UNESCO World Heritage Site since 2000.

Spurn Point at the mouth of the Humber Estuary in England is a fascinating example of a spit that has been breached repeatedly by storms. The narrow spit has been broken through and rebuilt multiple times over the centuries. A major breach in 2013 turned the tip into a temporary island, and natural processes have only partially reconnected it.

Ecology of Spits

• Salt Marshes: Sheltered water behind spits develops salt marsh ecosystems
• Dune Systems: Sand blown from the spit surface builds coastal dune habitats
• Bird Habitats: Spits and their sheltered lagoons attract diverse shorebirds and seabirds

The sheltered water behind a spit is one of its most ecologically important features. Protected from wave action, these calm areas accumulate fine sediment and develop into salt marshes or mudflats — some of the most productive ecosystems on Earth. Salt marshes behind spits provide nursery habitat for fish, feeding grounds for migratory birds, and buffers against flooding.

The spits themselves can support specialized coastal communities. Sand dune systems develop on broader spits, hosting marram grass, sea holly, and other dune plants. The interplay of dune, beach, marsh, and lagoon habitats creates a diverse mosaic that supports a wide range of species in a relatively small area.

Spits vs Other Coastal Features

• Spit vs Bar: A spit is attached to the coast at one end; a bar stretches across a bay mouth
• Spit vs Tombolo: A tombolo connects an island to the mainland; a spit extends into open water
• Spit vs Barrier Island: Barrier islands are larger and fully detached from the coast

Spits, bars, and barrier islands all form from sediment deposition but differ in their connection to the coast. A spit is attached to the mainland at one end and extends into the sea at the other. A bar extends completely across a bay mouth, enclosing a lagoon. A barrier island is a long, narrow island parallel to the coast, separated by a lagoon but not connected to the mainland.

These features can transition between forms. A growing spit may eventually extend across a bay mouth, becoming a bar. A bar can be breached by storms, becoming two spits. Understanding these transitions is important for coastal management, as the dynamic nature of these features means that any intervention must account for the ongoing movement of sediment.

Key Facts

• A spit is a narrow ridge of sand extending from the coast into the sea, formed by longshore drift.
• The Curonian Spit stretches 98 km along the Baltic coast of Lithuania and Russia.
• Spits form where the coastline changes direction, causing sediment to continue into open water.
• Salt marshes behind spits are among the most productive ecosystems on Earth.
• Most spits develop a recurved (hooked) tip due to wave refraction.

Fun Facts

• Spurn Point in England has been breached and rebuilt by storms multiple times over the centuries.
• The Curonian Spit is so narrow in places that you can see both the Baltic Sea and the lagoon at the same time.
• Farewell Spit in New Zealand extends 26 km and is one of the longest spits in the Southern Hemisphere.
• Sandy Hook, New Jersey, grows about 1 meter per year as longshore drift adds sediment to its tip.

Final Thoughts

Spits are among the most dynamic and elegant features of the coastline — narrow fingers of sand that grow, curve, and shift in response to waves and currents. They create sheltered waters that develop into salt marshes and lagoons, provide habitat for wildlife, and demonstrate the constructive power of longshore drift. Understanding spits is essential for coastal management, as these ever-changing features require approaches that work with natural processes rather than against them.