Govers, R., and Meijer, P. T., 2001. On the dynamics of the Juan de
Fuca plate. Earth and Planetary Science Letters, 189, 115–131.
Hager, B. H., and O’Connell, R. J., 1981. A simple global model of
plate dynamics and mantle convection. Journal of Geophysical
Research, 86, 4843–4867.
Harper, J. F., 1975. On the driving forces of plate tectonics. Geophysical Journal of the Royal Astronomical Society, 40, 465–474.
Lister, C. R. B., 1975. Gravitational drive on oceanic plates caused
by thermal contraction. Nature, 257, 663–665.
Lithgow-Bertelloni, C., and Richards, M. A., 1995. Cenozoic plate
driving forces. Geophysical Research Letters, 22, 1317–1320.
Lithgow-Bertelloni, C., and Silver P. G., 1998. Dynamic topography, plate driving forces and the African Superswell, Nature,
395, 269–272.
McKenzie, D. P., 1972. Plate tectonics. In Robertson, E. C. (ed.), The
Nature of the Solid Earth. New York: McGraw Hill, pp. 323–360.
Meade, B. J., and Conrad, C. P., 2008. Andean growth and the
deceleration of South American subduction: time evolution of
a coupled orogen-subduction system. Earth and Planetary Science Letters, 275, 93–101.
Ricard, Y., and Vigny, C., 1989. Mantle dynamics with induced plate
tectonics. Journal of Geophysical Research, 94, 17543–17560.
Richards, M. A., and Engebretson, D. C., 1992. Large-scale mantle
convection and the history of subduction. Nature, 355, 437–440.
Richards, M. A., Yang, W. S., Baumgardner, J. R., and Bunge, H. P.,
2001. Role of a low-viscosity zone in stabilizing plate tectonics:
implications for comparative terrestrial planetology. Geochemistry, Geophysics, Geosystems, 2, 2000GC000115
Solomon, S. C., and Sleep, N. H., 1974. Some simple physical
models for absolute plate motions. Journal of Geophysical
Research, 79, 2557–2567.
Stadler, G., Gurnis, M., Burstedde, C., Wilcox, L. C., Alisic, L., and
Ghattas, O., 2010. The dynamics of plate tectonics and mantle
flow: from local to global scales. Science, 329, 1033–1038.
Tackley, P. J., 2000. Mantle convection and plate tectonics: towards and
integrated physical and chemical theory. Science, 288, 2002–2007.
Turcotte, D. L., and Oxburgh, E. R., 1967. Finite amplitude convective cells and continental drift. Journal of Fluid Mechanics, 28,
29–42.
Turcotte, D. L., and Schubert, G., 2014. Geodynamics. Cambridge:
Cambridge University Press.
van Summeren, J., Conrad, C. P., and Lithgow-Bertelloni, C. R.,
2012. The importance of slab pull and a global asthenosphere
to plate motions. Geochemistry, Geophysics, Geosystems, 13,
Q0AK03.
Cross-references
Marine Heat Flow
Plate Motion
Plate Tectonics
Subduction
DUNES
Sara Muñoz-Vallés and Jesús Cambrollé
Department of Plant Biology and Ecology, University of
Sevilla, Seville, Spain
Definition
Dunes are sedimentary landforms originated by Aeolian
processes. More than simple accumulations of loose sand,
dunes show particular shapes with defined windward and
slip face slopes and an internal laminated structure due to
their formation dynamics of sand deposition. Adequate
supplies of well-sorted sands and winds capable of moving these sands for at least part of the year are required
to their formation, both in coastal and continental areas.
In the case of continental dunes, availability of sandy
sediments originated by desertification in emerged
lacustrine deposits or due to alteration of rocks can provide considerable sandy supplies. Under arid or semiarid
climate conditions, where vegetation is sparse or absent,
such deposits are mobilized by wind, resulting in the origination and development of dune fields such as the
existing in the Sahara, Arabian, Australian, Kalahari, or
Mohave deserts (García Mora, 2000). In the case of
coastal dunes, they are relatively complex phenomena that
form at the interface of terrestrial, oceanic, and atmospheric systems, where the influence from the sea and
the vegetation cover are relevant factors to their formation
and development. In addition, due to the joint action of
tides and wind-driven currents, submarine sand dunes
are also originated in continental shelves (Le Bot and
Trentesaux, 2004), while the existence of sandy bed material in rivers also promotes the formation of fluvial sand
dunes (Carling et al., 2000).
This entry focuses on coastal dunes as sedimentary
landforms and ecosystem and describes their occurrence,
typology, formation dynamics, and main ecological traits.
In addition, some information about environmental services and conservation is included.
Occurrence of coastal dunes
Coastal dunes are distributed worldwide, from polar to
tropical latitudes, comprising very diverse climates and
biomes, but covering a really limited global area
(Figure 1). They mainly develop in association with dissipative coasts dominated by marine winds, with an ample
supply of loose, sand-sized sediment (i.e., continental
shores, sandy barriers and spits), but they also occur on
lake and estuary shorelines (Carter, 1988; Martínez et al.,
2004). Coastal dunes present a large variety of forms
(see the subsection “Dune Typology” in this entry) and
dimensions (they range in size from less than 1 m to several kilometers) related with spatial and temporal variations in sediment supply and wind regime (Hesp, 2004;
Martínez et al., 2004; Pye and Tsoar, 2009). For instance,
dunes in geographical areas such as Australia show greater
developments and sizes due to the enormous volumes of
sand supply from the continental shelf, in contrast with
areas from USA or Europe, where dune systems show in
general smaller sizes and longitudinal developments due
to the action of the littoral drift currents (Sanjaume et al.,
2011). On the other hand, dune fields migrating obliquely
onshore to onshore (not alongshore), in very general
terms, are more common in the tropics and adjacent humid
subtropics than in temperate areas, where tabular dune
fields are more common (Hesp, 2004).
196
DUNES
Fuca plate. Earth and Planetary Science Letters, 189, 115–131.
Hager, B. H., and O’Connell, R. J., 1981. A simple global model of
plate dynamics and mantle convection. Journal of Geophysical
Research, 86, 4843–4867.
Harper, J. F., 1975. On the driving forces of plate tectonics. Geophysical Journal of the Royal Astronomical Society, 40, 465–474.
Lister, C. R. B., 1975. Gravitational drive on oceanic plates caused
by thermal contraction. Nature, 257, 663–665.
Lithgow-Bertelloni, C., and Richards, M. A., 1995. Cenozoic plate
driving forces. Geophysical Research Letters, 22, 1317–1320.
Lithgow-Bertelloni, C., and Silver P. G., 1998. Dynamic topography, plate driving forces and the African Superswell, Nature,
395, 269–272.
McKenzie, D. P., 1972. Plate tectonics. In Robertson, E. C. (ed.), The
Nature of the Solid Earth. New York: McGraw Hill, pp. 323–360.
Meade, B. J., and Conrad, C. P., 2008. Andean growth and the
deceleration of South American subduction: time evolution of
a coupled orogen-subduction system. Earth and Planetary Science Letters, 275, 93–101.
Ricard, Y., and Vigny, C., 1989. Mantle dynamics with induced plate
tectonics. Journal of Geophysical Research, 94, 17543–17560.
Richards, M. A., and Engebretson, D. C., 1992. Large-scale mantle
convection and the history of subduction. Nature, 355, 437–440.
Richards, M. A., Yang, W. S., Baumgardner, J. R., and Bunge, H. P.,
2001. Role of a low-viscosity zone in stabilizing plate tectonics:
implications for comparative terrestrial planetology. Geochemistry, Geophysics, Geosystems, 2, 2000GC000115
Solomon, S. C., and Sleep, N. H., 1974. Some simple physical
models for absolute plate motions. Journal of Geophysical
Research, 79, 2557–2567.
Stadler, G., Gurnis, M., Burstedde, C., Wilcox, L. C., Alisic, L., and
Ghattas, O., 2010. The dynamics of plate tectonics and mantle
flow: from local to global scales. Science, 329, 1033–1038.
Tackley, P. J., 2000. Mantle convection and plate tectonics: towards and
integrated physical and chemical theory. Science, 288, 2002–2007.
Turcotte, D. L., and Oxburgh, E. R., 1967. Finite amplitude convective cells and continental drift. Journal of Fluid Mechanics, 28,
29–42.
Turcotte, D. L., and Schubert, G., 2014. Geodynamics. Cambridge:
Cambridge University Press.
van Summeren, J., Conrad, C. P., and Lithgow-Bertelloni, C. R.,
2012. The importance of slab pull and a global asthenosphere
to plate motions. Geochemistry, Geophysics, Geosystems, 13,
Q0AK03.
Cross-references
Marine Heat Flow
Plate Motion
Plate Tectonics
Subduction
DUNES
Sara Muñoz-Vallés and Jesús Cambrollé
Department of Plant Biology and Ecology, University of
Sevilla, Seville, Spain
Definition
Dunes are sedimentary landforms originated by Aeolian
processes. More than simple accumulations of loose sand,
dunes show particular shapes with defined windward and
slip face slopes and an internal laminated structure due to
their formation dynamics of sand deposition. Adequate
supplies of well-sorted sands and winds capable of moving these sands for at least part of the year are required
to their formation, both in coastal and continental areas.
In the case of continental dunes, availability of sandy
sediments originated by desertification in emerged
lacustrine deposits or due to alteration of rocks can provide considerable sandy supplies. Under arid or semiarid
climate conditions, where vegetation is sparse or absent,
such deposits are mobilized by wind, resulting in the origination and development of dune fields such as the
existing in the Sahara, Arabian, Australian, Kalahari, or
Mohave deserts (García Mora, 2000). In the case of
coastal dunes, they are relatively complex phenomena that
form at the interface of terrestrial, oceanic, and atmospheric systems, where the influence from the sea and
the vegetation cover are relevant factors to their formation
and development. In addition, due to the joint action of
tides and wind-driven currents, submarine sand dunes
are also originated in continental shelves (Le Bot and
Trentesaux, 2004), while the existence of sandy bed material in rivers also promotes the formation of fluvial sand
dunes (Carling et al., 2000).
This entry focuses on coastal dunes as sedimentary
landforms and ecosystem and describes their occurrence,
typology, formation dynamics, and main ecological traits.
In addition, some information about environmental services and conservation is included.
Occurrence of coastal dunes
Coastal dunes are distributed worldwide, from polar to
tropical latitudes, comprising very diverse climates and
biomes, but covering a really limited global area
(Figure 1). They mainly develop in association with dissipative coasts dominated by marine winds, with an ample
supply of loose, sand-sized sediment (i.e., continental
shores, sandy barriers and spits), but they also occur on
lake and estuary shorelines (Carter, 1988; Martínez et al.,
2004). Coastal dunes present a large variety of forms
(see the subsection “Dune Typology” in this entry) and
dimensions (they range in size from less than 1 m to several kilometers) related with spatial and temporal variations in sediment supply and wind regime (Hesp, 2004;
Martínez et al., 2004; Pye and Tsoar, 2009). For instance,
dunes in geographical areas such as Australia show greater
developments and sizes due to the enormous volumes of
sand supply from the continental shelf, in contrast with
areas from USA or Europe, where dune systems show in
general smaller sizes and longitudinal developments due
to the action of the littoral drift currents (Sanjaume et al.,
2011). On the other hand, dune fields migrating obliquely
onshore to onshore (not alongshore), in very general
terms, are more common in the tropics and adjacent humid
subtropics than in temperate areas, where tabular dune
fields are more common (Hesp, 2004).
196
DUNES