73-548: Guadalupe-Nipomo Dunes is the largest remaining dune system south of San Francisco and the second largest in the U.S. state of California . It encompasses an 18-mile (29 km) stretch of coastline on the Central Coast of California and extends from southern San Luis Obispo County to northern Santa Barbara County . The Guadalupe-Nipomo Dunes Complex is home to a unique dunes ecosystem as well as many endangered and threatened species of plants and animals. To protect
146-619: A combination of factors including beach sand which was blown inland by the wind and the Santa Maria River which brought sediment to the coast. Dune-building began 18,000 years ago with the Nipomo and Orcutt Mesas. This Dune System has the highest dunes on the entire western coastline of the United States. Among these, Mussel Rock Dune is the highest, measuring approximately 500 feet (150 m). Another rare geographic treasure
219-589: A decrease in reproductive success. However, western snowy plover nests have increased dramatically from 16 nests in 1993 to a total of 172 nests in 2011. Memorial Day weekend is one of the park's busiest, and occurs during the plover nesting season. Yet, year after year, large numbers of plover nests are found at nesting sites closest to the open vehicle area at Oceano Dunes, suggesting human presence may deter presence of predators, and that plover may receive refuge at these sites. An eight-year summary of western snowy plover reproduction on California State Park lands depicts
292-562: A dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. Rotting seaweed , brought in by storm waves adds nutrients to allow pioneer species to colonize the dune. For example, in the United Kingdom these pioneer species are often marram grass , sea wort grass and other sea grasses. These plants are well adapted to
365-590: A few tens of metres except at their nose, where vegetation stops or slows the advance of accumulating sand. Simple parabolic dunes have only one set of arms that trail upwind, behind the leading nose. Compound parabolic dunes are coalesced features with several sets of trailing arms. Complex parabolic dunes include subsidiary superposed or coalesced forms, usually of barchanoid or linear shapes. Parabolic dunes, like crescent dunes, occur in areas where very strong winds are mostly unidirectional. Although these dunes are found in areas now characterized by variable wind speeds,
438-758: A leash at all times, and rid the beach of trash that could attract predators. During the busy holidays, extra rangers are brought into the park to ensure rules are enforced. For 25 years, the County of San Luis Obispo has leased 584 acres (2.36 km) of the Dunes to the State Department of Parks and Recreation, free of charge. When the lease expired in June 2008, the San Luis Obispo County Board of Supervisors had options, including sale of
511-407: A low-lying pan within the basin where the water evaporates, depositing the gypsum and forming crystals known as selenite . The crystals left behind by this process are eroded by the wind and deposited as vast white dune fields that resemble snow-covered landscapes. These types of dune are rare, and only form in closed arid basins that retain the highly soluble gypsum that would otherwise be washed into
584-412: A significant role in minimizing wave energy as it moves onshore. As a result, coastal dunes, especially those in the foredune area affected by a storm surge , will retreat or erode. To counteract the damage from tropical activity on coastal dunes, short term post-storm efforts can be made by individual agencies through fencing to help with sand accumulation. How much a dune erodes during any storm surge
657-462: A star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed. The sand mass of dunes can move either windward or leeward, depending on if the wind is making contact with the dune from below or above its apogee. If wind hits from above,
730-819: A unidirectional wind. In the sheltered troughs between highly developed seif dunes, barchans may be formed, because the wind is constrained to be unidirectional by the dunes. Seif dunes are common in the Sahara. They range up to 300 m (980 ft) in height and 300 km (190 mi) in length. In the southern third of the Arabian Peninsula, a vast erg , called the Rub' al Khali or Empty Quarter, contains seif dunes that stretch for almost 200 km (120 mi) and reach heights of over 300 m (980 ft). Linear loess hills known as pahas are superficially similar. These hills appear to have been formed during
803-518: Is Oso Flaco Lake, a freshwater lake located amid the Dunes. Even though the Guadalupe-Nipomo Dunes consist of moving sand with extremely low moisture that is seemingly deprived of nutrients, it is home to a variety of flora and fauna . There are at least 18 endangered species of plants living in the Dunes. Dune plants must also be able to endure burial by sand, salt spray, high winds, and high insolation. The Nipomo Mesa lupine
SECTION 10
#1732791180884876-485: Is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the colour of the rock. Cross-bedded layers of stacks of lithified dunes can produce the cross-hatching patterns, such as those seen in Zion National Park in the western United States. A slang term, used in
949-442: Is a very large aeolian landform, with a length of several kilometers and a height of tens to hundreds of meters, and which may have superimposed dunes. Dunes are made of sand-sized particles, and may consist of quartz, calcium carbonate, snow, gypsum, or other materials. The upwind/upstream/upcurrent side of the dune is called the stoss side; the downflow side is called the lee side. Sand is pushed (creep) or bounces ( saltation ) up
1022-410: Is blown along the beach. Dunes form where the beach is wide enough to allow for the accumulation of wind-blown sand, and where prevailing onshore winds tend to blow sand inland. The three key ingredients for coastal dune formation are a large sand supply, winds to move said sand supply, and a place for the sand supply to accumulate. Obstacles—for example, vegetation, pebbles and so on—tend to slow down
1095-445: Is by saltation , where sand particles skip along the ground like a bouncing ball . When these skipping particles land, they may knock into other particles and cause them to move as well, in a process known as creep . With slightly stronger winds, particles collide in mid-air, causing sheet flows . In a major dust storm , dunes may move tens of metres through such sheet flows. Also as in the case of snow, sand avalanches , falling down
1168-709: Is directly in the middle of the Oceano Dunes State Vehicular Recreation area. Various groups and individuals would like to see the land sold to the State Parks. Currently, the Oceano Dunes State Vehicular Recreation Area uses one third of the beach territory for off-road vehicles use. Off-roaders are concerned that since the decision is in the hands of the county, San Luis Obispo County's environmental community may advise more restrictions on
1241-428: Is due to a number of pressures related to their proximity to the ocean and confinement to growth on sandy substrates. These include: Plants have evolved many adaptations to cope with these pressures: In deserts where large amounts of limestone mountains surround a closed basin , such as at White Sands National Park in south-central New Mexico , occasional storm runoff transports dissolved limestone and gypsum into
1314-419: Is endemic to the dunes and is limited to the area. There are five to seven colonies growing in a strip of sand dunes. The dunes are separated into uplands and wetlands habitats. Uplands include the fore dunes, back dunes, and sandy beaches. Dunes can occur in three different formations. Primary Foredunes are parallel to the shore and support sparse vegetation. Parabolic dunes are U-shaped and perpendicular to
1387-404: Is related to its location on the coastal shoreline and the profile of the beach during a particular season. In those areas with harsher winter weather, during the summer a beach tends to take on more of a convex appearance due to gentler waves, while the same beach in the winter may take on more of a concave appearance. As a result, coastal dunes can get eroded much more quickly in the winter than in
1460-596: Is stimulated to grow by sand burial, causing a positive feedback. Many species of animals can be found among the dunes. Over 200 species of birds live there, such as the western snowy plover , American peregrine falcon , California brown pelican , and California least tern . Other animals also depend on the dunes such as the California red-legged frog , western terrestrial garter snake , mule deer , black bear , bobcats , and mountain lions . Beetles , butterflies , lizards , saltwater and freshwater fish inhabit
1533-593: The Sierra Club proposed year-round fencing to protect plover habitat, but the Oceano Dunes State Vehicular Recreation Area rejected the idea. Soon after the decision, a plover was killed by an off-road vehicle in a recommended area for fencing. The Sierra Club sued the State Parks for violating the ESA by not providing enough protection for the snowy plover, as well as the California least tern and steelhead trout. In
SECTION 20
#17327911808841606-523: The Western Desert of Egypt . The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than three kilometres, are in China's Taklamakan Desert . Abundant barchan dunes may merge into barchanoid ridges, which then grade into linear (or slightly sinuous) transverse dunes, so called because they lie transverse, or across, the wind direction, with the wind blowing perpendicular to
1679-459: The southwest US , for consolidated and hardened sand dunes is "slickrock", a name that was introduced by pioneers of the Old West because their steel-rimmed wagon wheels could not gain traction on the rock. Sand dunes can have a negative impact on humans when they encroach on human habitats. Sand dunes move via a few different means, all of them helped along by wind. One way that dunes can move
1752-659: The stoss (upflow) side, where the sand is pushed up the dune, and have a shorter slip face in the lee side. The valley or trough between dunes is called a dune slack . Dunes are most common in desert environments, where the lack of moisture hinders the growth of vegetation that would otherwise interfere with the development of dunes. However, sand deposits are not restricted to deserts, and dunes are also found along sea shores, along streams in semiarid climates, in areas of glacial outwash , and in other areas where poorly cemented sandstone bedrock disintegrates to produce an ample supply of loose sand. Subaqueous dunes can form from
1825-438: The Dunes and shot a skinny bear by the shores of what is now called Oso Flaco Lake. After eating the bear, two of the explorers became sick. The Chumash had poisoned the skinny bear - as a means of protection, they often incapacitated dangerous wildlife by feeding them tainted meat. This incident resulted in the lake's name: Oso Flaco or "Skinny Bear". In 1923, the epic movie The Ten Commandments directed by Cecil B. DeMille ,
1898-728: The San Luis Obispo Board of Supervisors voted 4-0 not to sell the 584 acres (2.36 km) of land to the State. Dune#Coastal dunes A dune is a landform composed of wind- or water-driven sand . It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex . A large dune complex is called a dune field , while broad, flat regions covered with wind-swept sand or dunes, with little or no vegetation, are called ergs or sand seas . Dunes occur in different shapes and sizes, but most kinds of dunes are longer on
1971-551: The action of water flow ( fluvial processes) on sand or gravel beds of rivers , estuaries , and the sea-bed. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach . In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea . Artificial dunes are sometimes constructed to protect coastal areas. The dynamic action of wind and water can sometimes cause dunes to drift, which can have serious consequences. For example,
2044-568: The breeding success at Oceano Dunes which is particularly stark compared to very low breeding numbers elsewhere in the state. Ecologists argue that the snowy plover does not just breed on any coastal area; they seek protection in the dunes. Scientist Tom Jordan studied data on bird nesting sites and found that snowy plovers "prefer the beach and the flatter areas," such as on top of the dunes, where they can watch for predators. Plovers prefer nesting on open sand which can put nests at risk of being crushed by vehicles or hikers. The Santa Lucia Chapter of
2117-530: The case settlement, the State Park was given the responsibility of researching, fund raising, and establishing an education program about the snowy plover. The Park must close off an additional half-mile of the beach between March and October, the plover's breeding season. Additionally, they must find alternate routes to avoid vehicles crossing the Arroyo Grande Creek because it is inhabited by
2190-409: The coastal environment of the sand dune vital to their species' survival. Over the course of time coastal dunes may be impacted by tropical cyclones or other intense storm activity, dependent on their location. Recent work has suggested that coastal dunes tend to evolve toward a high or low morphology depending on the growth rate of dunes relative to storm frequency. During a storm event, dunes play
2263-608: The concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below). Some types of crescentic dunes move more quickly over desert surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 in China 's Ningxia Province , and similar speeds have been recorded in
Guadalupe-Nipomo Dunes - Misplaced Pages Continue
2336-405: The corridors between individual dunes. Because all dune arms are oriented in the same direction, and, the inter-dune corridors are generally swept clear of loose sand, the corridors can usually be traversed in between the trailing arms of the dune. However to cross straight over the dune by going over the trailing arms, can be very difficult. Also, traversing the nose is very difficult as well because
2409-608: The counties of San Luis Obispo and Santa Barbara, California State Parks , U.S. Fish and Wildlife Service and the Land Conservancy of San Luis Obispo County. The first known inhabitants of the Guadalupe-Nipomo Dunes were Native Americans of the Chumash tribe; early Spanish maritime explorers noted their settlements. However, Europeans did not travel through the Dunes themselves until September 2–4, 1769, when members of Don Gaspar de Portolà 's overland expedition stayed in
2482-496: The direction (s) of prevailing winds, are known as lunettes, source-bordering dunes, bourrelets and clay dunes. They may be composed of clay, silt, sand, or gypsum, eroded from the basin floor or shore, transported up the concave side of the dune, and deposited on the convex side. Examples in Australia are up to 6.5 km long, 1 km wide, and up to 50 metres high. They also occur in southern and West Africa , and in parts of
2555-682: The distance between the water line and where vegetation can grow. Coastal dunes can be classified by where they develop, or begin to take shape. Dunes are commonly grouped into either the Primary Dune Group or the Secondary Dune Group. Primary dunes gain most of their sand from the beach itself, while secondary dunes gain their sand from the primary dune. Along the Florida Panhandle, most dunes are considered to be foredunes or hummocks. Different locations around
2628-604: The dune and underlying soils . The stability of the dunes was once attributed to the vegetative cover but recent research has pointed to water as the main source of parabolic dune stability. The vegetation that covers them—grasses, shrubs, and trees—help anchor the trailing arms. In inland deserts, parabolic dunes commonly originate and extend downwind from blowouts in sand sheets only partly anchored by vegetation. They can also originate from beach sands and extend inland into vegetated areas in coastal zones and on shores of large lakes. Most parabolic dunes do not reach heights higher than
2701-513: The dunes and provide horticultural benefits, but instead spread taking land away from native species. Ammophila arenaria , known as European beachgrass, has a similar story, though it has no horticulture benefits. It has great ground coverage and, as intended, stabilized the dunes but as an unintended side effect prevented native species from thriving in those dunes. One such example is the dune field at Point Reyes, California . There are now efforts to get rid of both of these invasive species. As
2774-452: The dunes as well. The dunes have been involved with an ongoing series of environmental debates regarding the reduced air quality found in the receiving towns downwind of the dune system. Physical effects by the dust aerosols are indicated by accounts of homeowners claiming discomfort in breathing during times of high dust concentration, and air quality measurements. The San Luis Obispo County Air Pollution Control District has been researching
2847-466: The dunes environment, much of the Complex has been set aside for conservation. In addition, it is recognized as a National Natural Landmark . Another portion of the Dunes is utilized for recreation, such as camping and off-highway vehicle (OHV) use. The Guadalupe-Nipomo Dunes is owned by a number of federal, state, and local agencies, and private companies, organizations and individuals. These include
2920-517: The dunes shift. Portions of Beyoncé 's Black Is King were filmed on the Dunes in 2019. From the 1920s until the 1940s, a group of mystics, nudists, artists, writers, and hermits known as the "Dunites" inhabited the Dunes. They regarded the Dunes as a center of creative energy. Gavin Arthur founded this art and literature commune and a magazine called "The Dune Forum". At the same time, oil companies had started buying up Dune land, and in 1948 oil
2993-598: The dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks' soil to be waterlogged where only marsh plants can survive. In Europe these plants include: creeping willow, cotton grass, yellow iris , reeds, and rushes. As for vertebrates in European dunes, natterjack toads sometimes breed here. Dune ecosystems are extremely difficult places for plants to survive. This
Guadalupe-Nipomo Dunes - Misplaced Pages Continue
3066-592: The dunes. Typically these are heather , heaths and gorses . These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration. Heather adds humus to the soil and is usually replaced by coniferous trees, which can tolerate low soil pH , caused by the accumulation and decomposition of organic matter with nitrate leaching. Coniferous forests and heathland are common climax communities for sand dune systems. Young dunes are called yellow dunes and dunes which have high humus content are called grey dunes . Leaching occurs on
3139-401: The effective winds associated with the growth and migration of both the parabolic and crescent dunes probably are the most consistent in wind direction. The grain size for these well-sorted, very fine to medium sands is about 0.06 to 0.5 mm. Parabolic dunes have loose sand and steep slopes only on their outer flanks. The inner slopes are mostly well packed and anchored by vegetation, as are
3212-519: The geological record . All these dune shapes may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). Simple dunes are basic forms with the minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed. Complex dunes are combinations of two or more dune types. A crescentic dune with
3285-595: The globe have dune formations unique to their given coastal profile. Coastal sand dunes can provide privacy and/or habitats to support local flora and fauna. Animals such as sand snakes, lizards, and rodents can live in coastal sand dunes, along with insects of all types. Often the vegetation of sand dunes is discussed without acknowledging the importance that coastal dunes have for animals. Further, some animals, such as foxes and feral pigs can use coastal dunes as hunting grounds to find food. Birds are also known to utilize coastal dunes as nesting grounds. All these species find
3358-638: The ground to avoid the wind and others adopt a Krummholz growth form. The back dunes, just behind the fore dunes, are stabilized and covered with plants. The back dunes are dominated by shrub species like mock heather, dune lupine, coastal buckwheat, and blochman's senecio. The sandy beaches are a harsh environment with no plants able to survive there. The wetlands include the areas that contain water: salt marshes , fresh and brackish-water marshes, swamps , and mudflats . Plants that live there are adapted to dynamic environmental conditions including high salinity concentration and extreme temperatures. Solutions that
3431-408: The harsh conditions of the foredune, typically having deep roots which reach the water table , root nodules that produce nitrogen compounds, and protected stoma , reducing transpiration . Also, the deep roots bind the sand together, and the dune grows into a foredune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonize
3504-429: The land if it isn't sold. Land available for vehicle use has already been reduced from 15,000 acres (61 km) to 1,500 acres (6.1 km). The State wants to buy the land in order to secure a place for off-road vehicles for the future. They claim not all the land would be used for off-road vehicles and camping, and that part of the land would be set aside as preserve areas, as the County wants. On Tuesday April 17, 2007,
3577-457: The land, renewal of the deal with the state or creation of a deal requiring the state to pay rent. To determine whether or not to sell the dune property to the state, two public hearings were held April 17, 2007. To sell real property, four-fifths of the supervisors must vote in favor; but in order to renew a lease only a majority is required. The State Parks offered to pay $ 4.86 million for nearly 584 acres (2.36 km) of beachfront property that
3650-486: The last ice age under permafrost conditions dominated by sparse tundra vegetation. Star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around
3723-521: The margins of the sand seas , particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth. Oval or circular mounds that generally lack a slipface. Dome dunes are rare and occur at the far upwind margins of sand seas. Fixed crescentic dunes that form on the leeward margins of playas and river valleys in arid and semiarid regions in response to
SECTION 50
#17327911808843796-658: The nose is usually made up of loose sand without much if any vegetation. A type of extensive parabolic dune that lacks discernible slipfaces and has mostly coarse grained sand is known as a zibar . The term zibar comes from the Arabic word to describe "rolling transverse ridges ... with a hard surface". The dunes are small, have low relief, and can be found in many places across the planet from Wyoming (United States) to Saudi Arabia to Australia. Spacing between zibars ranges from 50 to 400 metres and they do not become more than 10 metres high. The dunes form at about ninety degrees to
3869-443: The plants can take to adapt to high salinity are large tap roots to reach the perched water table, thick cuticle to prevent water loss, and succulence. Weeds have been introduced into the Dunes environment both purposefully and accidentally and threaten the native plant life. Various native plants are being choked out by invasive species like European beach grass. European beach grass achieves higher cover than native dune grass and
3942-440: The prevailing wind which blows away the small, fine-grained sand leaving behind the coarser grained sand to form the crest. Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above shapes. These dunes typically have major and minor slipfaces oriented in opposite directions. The minor slipfaces are usually temporary, as they appear after a reverse wind and are generally destroyed when
4015-596: The reduced air quality downwind of the Oceano Dunes SVRA since 1995, and has concluded that while there is a natural component to the dust pollution, off-highway vehicular activity makes it worse. Off-road vehicle use partially conflicts with habitat of the western snowy plover ( Charadrius nivosus ) which was listed as threatened under the Endangered Species Act (ESA) on March 5, 1993. It is alleged that use by vehicles directly correlates with
4088-484: The resultant direction of sand movement (hence the name "longitudinal"). Some linear dunes merge to form Y-shaped compound dunes. Formation is debated. Ralph Bagnold , in The Physics of Blown Sand and Desert Dunes , suggested that some seif dunes form when a barchan dune moves into a bidirectional wind regime, and one arm or wing of the crescent elongates. Others suggest that seif dunes are formed by vortices in
4161-479: The ridge crest. Seif dunes are linear (or slightly sinuous) dunes with two slip faces. The two slip faces make them sharp-crested. They are called seif dunes after the Arabic word for "sword". They may be more than 160 kilometres (100 miles) long, and thus easily visible in satellite images (see illustrations). Seif dunes are associated with bidirectional winds. The long axes and ridges of these dunes extend along
4234-415: The sand in the dune migrates forward. In plan view, these are U-shaped or V-shaped mounds of well-sorted, very fine to medium sand with elongated arms that extend upwind behind the central part of the dune. There are slipfaces that often occur on the outer side of the nose and on the outer slopes of the arms. These dunes often occur in semiarid areas where the precipitation is retained in the lower parts of
4307-425: The sand particles move leeward; the leeward flux of sand is greater than the windward flux. Conversely, if sand hits from below, sand particles move windward. Further, if the wind is carrying sand particles when it hits the dune, the dune's sand particles will saltate more than if the wind had hit the dune without carrying sand particles. Coastal dunes form when wet sand is deposited along the coast and dries out and
4380-438: The sea. A nabkha , or coppice dune, is a small dune anchored by vegetation. They usually indicate desertification or soil erosion, and serve as nesting and burrow sites for animals. Sub-aqueous ( underwater ) dunes form on a bed of sand or gravel under the actions of water flow. They are ubiquitous in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Dunes move downstream as
4453-458: The shore with vegetative ridges. Moving sand sheets consist of constantly moving sand, making it hard for vegetation to settle. The fore dunes begin at the high tide line, where only low growing plants with deep root systems (such as sand verbena ) can live. The strong winds, salt spray, and massive amounts of sand make this area uninhabitable for other types of plants. Plants in the dunes adapt growth forms to survive high winds. Some grow close to
SECTION 60
#17327911808844526-537: The steelhead trout. Within the Guadalupe-Nipomo Dunes Complex are several distinct regions, each managed by different organizations and used for various purposes. The Oceano State Vehicular Recreation Area has taken measures to protect wildlife by fencing off specific areas from pedestrians and vehicles and creating rules for visitors. Some rules are: adhere to the 15 mph (24 km/h) speed limit, do not enter closed areas, keep dogs on
4599-402: The steeper slip face facing downstream. Ripple marks preserved in sedimentary strata in the geological record can be used to determine the direction of current flow, and thus an indication of the source of the sediments. Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding . A lithified (consolidated) sand dune
4672-604: The stoss side, and slides down the lee side. A side of a dune that the sand has slid down is called a slip face (or slipface). The Bagnold formula gives the speed at which particles can be transported. Five basic dune types are recognized: crescentic, linear, star, dome, and parabolic. Dune areas may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on
4745-620: The summer. The converse is true in areas with harsher summer weather. There are many threats to these coastal communities. Some coastal dunes, for example ones in San Francisco, have been completely altered by urbanization; reshaping the dune for human use. This puts native species at risk. Another danger, in California and places in the UK specifically, is the introduction of invasive species. Plant species, such as Carpobrotus edulis , were introduced from South Africa in an attempt to stabilize
4818-509: The town of Eucla, Western Australia , had to be relocated in the 1890s because of dune drift. The modern word "dune" came into English from French around 1790, which in turn came from Middle Dutch dūne . A universally precise distinction does not exist between ripples, dunes, and draas , which are all deposits of the same type of materials. Dunes are generally defined as greater than 7 cm tall and may have ripples, while ripples are deposits that are less than 3 cm tall. A draa
4891-471: The upstream slope is eroded and the sediment deposited on the downstream or lee slope in typical bedform construction. In the case of sub-aqueous barchan dunes, sediment is lost by their extremities, known as horns. These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. The shape of a dune gives information about its formation environment. For instance, rivers produce asymmetrical ripples, with
4964-534: The western United States, especially Texas. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. The elongated arms are held in place by vegetation; the largest arm known on Earth reaches 12 km. Sometimes these dunes are called U-shaped, blowout , or hairpin dunes, and they are well known in coastal deserts. Unlike crescent shaped dunes, their crests point upwind. The bulk of
5037-402: The wind and lead to the deposition of sand grains. These small "incipient dunes or "shadow dunes" tend to grow in the vertical direction if the obstacle slowing the wind can also grow vertically (i.e., vegetation). Coastal dunes expand laterally as a result of lateral growth of coastal plants via seed or rhizome . Models of coastal dunes suggest that their final equilibrium height is related to
5110-483: The wind next blows in the dominant direction. Draas are very large-scale dune bedforms; they may be tens or a few hundreds of metres in height, kilometres wide, and hundreds of kilometres in length. After a draa has reached a certain size, it generally develops superimposed dune forms. They are thought to be more ancient and slower-moving than smaller dunes, and to form by vertical growth of existing dunes. Draas are widespread in sand seas and are well-represented in
5183-668: Was discovered in the Dunes. The oil company Unocal began operating the Guadalupe Oil Field in the 1950s. Over the course of the next forty years, Unocal leaked 18 million gallons of petroleum under the Dunes. In 1994, the company publicly recognized the spill and began cleaning up the 2,700-acre (11 km) site, which lies in San Luis Obispo County immediately north of the Santa Barbara County line. As of 2015, cleanup and restoration work
5256-469: Was expected to continue for at least another 10 years. Starting in the 1970s, measures were taken to protect the natural environment at the Dunes. One of the biggest changes was the restriction of OHVs to the designated Oceano Dunes State Vehicular Recreation Area. This allowed for the other areas of the Dunes to undergo restoration efforts by conservation groups. As of 2013 the process of dune restoration continues. The Guadalupe-Nipomo Dunes were formed by
5329-625: Was filmed on the Dunes. At the end of production, the massive sets reproducing ancient Egypt were dismantled and buried on the site to prevent reuse. The location was later used to film the episode "White Tip's Journey" (set in Late Cretaceous Mongolia ) of the dinosaur documentary miniseries Dinosaur Planet in 2004. As of 2013 they remain buried there, despite decades of various proposals for excavation. Some artifacts have been recovered and are on display at The Dunes Visitor Center, while others may be seen from time to time as
#883116