A
spit or
sandspit is a
depositionDeposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment gravity flows, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of...
landformIn the earth sciences and geology sub-fields, a landform or physical feature comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
found off coasts. At one end, spits connect to land, while at the far end they exist in open water. A spit is a type of
barA shoal, sandbar , or gravebar is a somewhat linear landform within or extending into a body of water, typically composed of sand, silt or small pebbles. A spit or sandspit is a type of shoal...
or
beachA beach is a geological landform along the shoreline of a body of water. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones...
that develops where a re-entrant occurs, such as at cove's headlands, by the process of
longshore driftLongshore drift, sometimes known as drifting, longshore current, LSD or littoral drift is the movement of sediments, most often sand, along a coast parallel to its shoreline....
. Longshore drift (also called littoral drift) occurs due to waves meeting the beach at an oblique angle, and backwashing perpendicular to the shore, moving sediment down the beach in a zigzag pattern. Longshore drifting is complemented by longshore currents, which
transport sedimentThe phrase Sediment transport is used to describe the movement of solid particles and the processes that govern their motion. Sediment transport is typically due to a combination of the force of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained...
through the water alongside the beach. These currents are set in motion by the same oblique angle of entering waves that causes littoral drift and transport sediment in a similar process.
Hydrology and geology
Where the direction of the shore inland
reenters, or changes direction, such as at a headland, the longshore current spreads out or dissipates. No longer able to carry the full load, much of the sediment is dropped. This is also known as deposition. This submerged bar of sediment allows littoral drift to continue to transport in the direction the waves are breaking, forming an above-water spit. Without the complementary process of littoral drift, the bar would not build above the surface of the waves becoming a spit and would instead be leveled off underwater.
Spits occur when
longshore driftLongshore drift, sometimes known as drifting, longshore current, LSD or littoral drift is the movement of sediments, most often sand, along a coast parallel to its shoreline....
reaches a section of
headlandA headland is land surrounded by water on three sides.Headland can also refer to:*Headlands and bays*headLand, an Australian television series*Headland , the area at each end of a planted field used for turning farm machinery...
where the turn is greater than 30 degrees. They will continue out into the sea until water pressure (such as from a river) becomes too much to allow the sand to deposit. The spit may then be grown upon and become stable and often fertile. A spit may be considered a specialized form of a
shoalThings known as shoal, shoals or shoaling include:* Shoal, a sandbank or reef creating shallow water, especially where it forms a hazard to shipping* Shoal draught , of a boat with shallow draught which can pass over some shoals...
. As spits grow, the water behind them is sheltered from wind and waves, and a salt marsh is likely to develop.
Wave refraction can occur at the end of a spit, carrying sediment around the end to form a hook or recurved spit. Wave refraction in multiple directions will cause a complex spit to form. Incoming waves that come in a direction other than obliquely along the spit will halt the growth of the spit, shorten it or eventually destroy it entirely.
The sediments that make up spits come from a variety of sources including rivers and eroding bluffs, and changes there can have a large impact on spits and other coastal landforms. Activities such as logging and farming upstream can increase the sediment load of rivers, which may hurt the intertidal environments around spits by smothering delicate habitat. Roads or bulkheads built along bluffs can drastically reduce the volume of sediment eroded, so that not enough material is being pushed along to maintain a given spit.
If the supply of sediment is interrupted the sand at the neck (landward side) of the spit may be moved towards the head, eventually creating an
islandAn island or isle is any piece of land that is surrounded by water. Very small islands such as emergent land features on atolls are called islets. A key or cay is another name for a small island or islet. An island in a river or lake may be called an eyot, .There are two main types of islands:...
. If the supply isn't interrupted, and the spit isn't breached by the sea (or, if across an estuary, the river) the spit may become a
barA shoal, sandbar , or gravebar is a somewhat linear landform within or extending into a body of water, typically composed of sand, silt or small pebbles. A spit or sandspit is a type of shoal...
, with both ends joined to land, and form a
lagoonA lagoon is a body of comparatively shallow salt or brackish water separated from the deeper sea by a shallow or exposed sandbank, coral reef, or similar feature. Thus, the enclosed body of water behind a barrier reef or barrier islands or enclosed by an atoll reef is called a lagoon. This...
behind the bar. If an island lies offshore near where the coast changes direction, and the spit continues to grow until it connects the island to the mainland, it is then called a
tomboloA tombolo or sometimes ayre is a deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar. Once attached the island is then known as a tied island...
.
The end of a spit attached to land is called the proximal end, and the end jutting out into water is called the distal end.
Spits around the world
The longest spit in the World is the
Curonian SpitThe Curonian Spit is a 98 km long, thin, curved sand-dune spit that separates the Curonian Lagoon from the Baltic Sea.-Geography:The Curonian Spit stretches from the Sambian Peninsula on the south to its northern tip next to a narrow strait, across which is the port city of Klaipėda on the...
in the
Baltic SeaThe Baltic Sea is a brackish inland sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and the...
, famous by its unique landscape and ecosystem. It is almost 100 km long, evenly divided between
RussiaRussia , officially known as both Russia and the Russian Federation , is a country in northern Eurasia . It is a semi-presidential republic, comprising 83 federal subjects...
and
LithuaniaLithuania , officially the Republic of Lithuania is a country in Northern Europe, the southernmost of the three Baltic states. Situated along the southeastern shore of the Baltic Sea, it shares borders with Latvia to the north, Belarus to the southeast, Poland, and the Russian exclave of...
.
The largest spit in the United States is the
Dungeness SpitDungeness Spit is a long sand spit jutting out from the northern edge of the Olympic Peninsula in northeastern Clallam County, Washington, into the Strait of Juan de Fuca. It is entirely within the Dungeness National Wildlife Refuge and home of the Dungeness Lighthouse. It is the longest natural...
on the
Olympic Peninsula|||The Olympic Peninsula is the large arm of land in western Washington state of the USA, that lies across Puget Sound from Seattle. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, and the east by Puget Sound and the Hood Canal...
in
WashingtonWashington is a state in the Pacific Northwest region of the United States. Washington was carved out of the western part of Washington Territory which had been ceded by Britain in 1846 by the Oregon Treaty as settlement of the Oregon Boundary Dispute. It was admitted to the Union as the...
(8.9 km).
Farewell SpitFarewell Spit is a narrow sand spit situated at , at the northern end of the South Island of New Zealand. Known to the Māori as Tuhuroa, it runs eastwards from Cape Farewell, the island's northernmost point...
in
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
, at 32 km, is one of the longest in the world. Farewell Spit, in the North West corner of the
South IslandThe South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
is believed to be caused by the strong prevailing winds and currents bringing sand eroded from the
Southern AlpsThe Southern Alps is a mountain range which runs along the western side of the South Island of New Zealand. It forms a natural dividing range along the entire length of the South Island. The term "Southern Alps" generally refers to the entire range, although separate names are given to many of the...
of the South Island and depositing these into Golden Bay.
Spits in the UK are caused by prevailing South-Westerly winds, which give the spits their direction. However, when the direction of the wind changes for a short while the spit may change in direction for a short while forming a hook. Many spits have hooked or curved ends. One spit in the UK can be found in
DorsetDorset , is a county in South West England on the English Channel coast. The county town has been Dorchester since at least 1305, situated in the south of the county at . Between its extreme points Dorset measures from east to west and north to south, and has an area of...
.
Chesil BeachChesil Beach, sometimes called Chesil Bank, in Dorset, southern England is one of three major shingle structures in Britain. Its toponym is derived from the Old English ceosel or cisel, meaning "gravel" or "shingle"....
is an 18 mile long shingle that connects
WeymouthWeymouth is a large town in Dorset, England, situated on a sheltered bay at the mouth of the River Wey on the English Channel coast. The town is south of Dorchester and north of the Isle of Portland. The town's population is around 54,000....
to the Isle of Portland. Chesil Beach provides shelter to Weymouth and the village of Chiswell from prevailing winds and waves.
Human settlement patterns
Since prehistory humans have chosen certain spit formations as sites for human habitation. In some cases such as
ChumashThe "Chumash" are Native American people who historically inhabit chiefly central and southern coastal regions of California, in portions of what is now San Luis Obispo, Santa Barbara, Ventura and Los Angeles counties, extending from Morro Bay in the north to Malibu in the south...
Native AmericanThe indigenous peoples of the Americas are the pre-Columbian inhabitants of the Americas, their descendants, and many ethnic groups who identify with those peoples...
prehistorical settlement, these sites have been chosen for proximity to marine resource exploitation; for example, the Chumash settlement on the Morro Bay sandspit is one such location.