CHARACTERIZATION OF SANDS IN THE BEACH-DUNE

CHARACTERIZATION OF SANDS IN THE BEACH-DUNE SYSTEMS
OF THE EASTERN CANARY ISLANDS (SPAIN)
Mangas, José (1); Pérez-Chacón, Emma (2); Hernández-Calvento, Luis (2); Alonso, Ignacio (1); Cabrera, Laura Luisa (1)
Hernández-Cordero, Antonio I. (2); Menéndez, Inmaculada (1) and Sánchez-Pérez, Isora (1)
(1) Group of Applied and Regional Geology (GEOGAR). Department of Physics ([email protected])
(2) Group of Physical Geography and Environment. Department of Geography.
University of Las Palmas de Gran Canaria. 35017 Las Palmas de Gran Canaria (Spain)
Investigations carried out in the REN 2003-05947 and SEJ2007-64959-GEOG projects, financed by FEDER and spanish MSI founds
The Canary archipelago, associated with an oceanic
intraplate hot spot, has mainly beach-dune systems
in the eastern islands which present a remarkably
ecological (protected natural areas) and economical
(tourism industry) interest. The work has been
carried out in the beach-dune systems of
Maspalomas (Gran Canaria Island), Corralejo
(Fuerteventura Island), Famara (Lanzarote Island)
and La Graciosa Islet.
Fuerteventura
Gran Canaria
Lanzarote
La Graciosa
THE SEDIMENTARY DEFICIT
Over the last decades, these coastal systems show evidence of a sedimentary deficit which, in some fields, means the erosion onto beaches and dunes that are essential for the tourist
activity. In this context, our research teams are developing several multidisciplinary projects for elaborating a diagnosis on this situation applying a scientific base, for determining the
causes of the sedimentary deficit and for proposing different solutions.
BEACH-DUNE SYSTEM OF
MASPALOMAS (GRAN CANARIA
ISLAND)
Sedimentary terrace of El Inglés
El Inglés Beach
The development of the tourism in the
neighbourhood of the protected area
Las Dunas de Maspalomas has been
progressive from the Sixties of 20th
Century to nowadays (3 millions
tourists/year).
The urbanization of the El Ingles'
sedimentary terrace has modified the
aeolian sedimentary dynamics,
generating the stabilization of the aeolian
deposits in insides areas, the
appearance of geological materials that
constitute the underlying basement of
the dunes area and the erosion onto
dunes and beaches.
The analysis of aerial photographies of
last decades shows an increase in the
exhumed surfaces of this basement from
2
2
70.000 m in 1960, to 170.000 m in 2003.
The lost sand of the dune system
3
calculed by DEM is the 7.500.000 m in
this periode.
Maspalomas Beach
1960
2006
2006
EROSION RATES IN BEACHES (m)
El Inglés beach
El Inglés sedimentary terrace
Maspalomas beach
Stabilized dunes
Deflation zones
Mobile dunes
Fore dune
Beach
2008
BEACH-DUNE SYSTEM OF CORRALEJO NATURAL PARK
(LANZAROTE ISLAND)
Sand explotation in the Corralejo dune
field at the 80 decade
Beachrock outcrop at Cateta Bajo Negro
2008
Outcrop of basaltic lava flow at Punta de Tivas
Stabilized aeolian deposit at the south of Corralejo
town
Fernández Galvan et al., 1982
Urban development at Corralejo area (Fuerventura Island) between 1969 and today has modified the aeolian dinamyc cuting the entry of marine sediments in the direction of dune field. These processes have produced a sediment deficit
in the Corralejo Natural Park, with erosion onto beaches (beachrock and lava flow outcrops) and stabilization of aeolian sand deposits.
Corralejo Natural Park
(Fuerteventura Island)
BEACH-DUNE SYSTEMS OF THE ARCHIPIELAGO CHINIJO NATURAL PARK (LANZAROTE ISLAND AND LA GRACIOSA ISLET)
The beach-dune systems of Bahia de Penedo (Lanzarote) and Caleta del Sebo-El Salado (La Graciosa) show a sedimentary deficit with the disappearance of mobile dunes, nebkas, aeolian deposits
stabilized, and the beach erosion with the appearance of beachrocks and volcanic lava flows.
1977
La Graciosa Islet
1987
2009
Beachrock outcrop at the Salado Beach
Caleta del
Sebo
Environmental changes in Bahia de Penedo (Caleta de Famara
town, Lanzarote Island) from 1955 to 2008
Temporal evolution of urban development at Caleta del Sebo (La
Graciosa Islet) from 1977 to 2009
El Salado
Beach
Lanzarote Island
GEOLOGICAL CHARACTERISTICS OF SANDS IN THE BEACH-DUNE SYSTEMS AND DIAGNOSIS
It is important, among other things, to characterize the sands to determine the area source of these sediments, with the purpose of studying the causes of this sedimentary deficit in
depth. This is an aim of the research, whose methodology is based on the sedimentologic and petrographic studies of sand samples, which have been selected from environmental units
to focus on the ecological features of the sedimentary systems studied.
These beach-dune systems show composition and texture diversity due to the source areas of the sands are different and the environmental conditions are variable. In general, the
bioclasts studied (essencially seaweed meshes and mollusks) come from coastal environments and/or from shallow platform, and lithoclasts (volcanic rock and mineral fragments, with
absence of quartz) originated by the fluvial or marine erosion of the volcanic and sedimentary materials which appear in the surroundings of every beach-dune system.
The causes of sedimentary deficit can be natural (less of bioclasts and litoclasts due to changes of oceanographic factors) and antropogenic (urban development modifies aeolian and
marine dinamyc, and environmental conditions).
Granulometric and petrographic studies of onshore and offshore sand samples
from Maspalomas beach-dune system
Granulometric and petrographic studies of sand samples from Corralejo beach-dune system
GRAIN SIZE
Granulometric and petrographic studies of sand samples from Archipiélago Chinijo Natural Park
beach-dune systems (Lanzarote y La Graciosa)
Famara Beach (Bahia de Penedo)
Famara beach and beachrock
BEACH
GRAIN SIZE
Famara beach and nebkas
DUNE
% CARBONATES
Medium size distribution of sediment in the studied zone. Circle size
is porportional to the same (max: 0.91 mm, min: 0.24 mm) [O:mobile
dunes, O: fosil dunes and aeolianites, O: beaches]
SORTING
El Ambar Beach with outcrops of beachrock
and lava flow
Beach sands of the Ambar Beach
BEACH
BEACH
Sorting distribution of sediment in the studied zone. Circle size is
porportional to the same (max: 2.454 mm, min: 0.387 mm) [O:mobile
dunes, O: fosil dunes and aeolianites, O: beaches]
DUNE
Hummock dunes (Nebkas) of the Ambar