Germán Flor-Blanco

Raised Beaches in the Cantabrian Coast

Raised beaches along the Cantabrian coast are related to erosion surfaces, locally known as rasas, affected by tectonic uplift. The higher surfaces, probably of Pliocene age, have a maximum relative height of 285 m above mean sea level (MSL). Generally, they have gentle seaward slopes and highly variable lateral and longitudinal distribution. They reach 20 km in maximum width in central Asturias, and the lower levels cover smaller areas. Two W-E-oriented zones may be differentiated along the coast: Burela-Nalon (107 km) and Nalon-France (365 km). Two or three levels of rasas were generated in the first sector, which gradually merge into one towards the west. In the Nalon-France zone, 12 levels have been recognised. These geomorphic surfaces are apparently slightly deformed, although some authors proposed that they are strongly faulted. Some aggradation and fluvial terraces, abrasion surfaces, as well aeolian sand deposits, can be correlated with rasa levels. Other old deposits disconnected from the rasas were generated associated with exposed and estuarine beaches and may include slope deposits less than 1.0 m thick. Most beach and aeolian dune deposits are siliciclastic, with a limited proportion of bioclastic sands and debris. Relevant pending issues to be resolved are the numerical age of the rasas and their possible correlation with erosion surfaces, eustatic changes and uplift, considering that neotectonic activity is thought to be low and localised. The most recent marine terraces have not been uplifted and are affected by a general recession due to sea-level rise.

Evolution of beach–dune fields systems following the construction of jetties in estuarine mouths (Cantabrian coast, NW Spain)

Abstract The morphology of many Spanish estuarine mouths has been modified over recent decades to improve access to the harbours located inside. The normal practice has been the construction of jetties along one or both sides of the mouth to improve the flow though the main estuarine channel and thereby prevent the formation of bars in the main channel bed and ebb-tidal delta lobes or mouth bars in the mouths. The new wave refraction/diffraction dynamics created by these structures induces a strong modification of the beach–dune systems. In the zones adjacent to the jetties, a rapid migration occurs until the beach profile and the associated dune field stabilise, which occurs when the confined space is unable to retain more sediment. This process may include the reworking of outer sandy bottoms and the generation of new stabilised bars. A portion of the sand used by waves to form this accretion is supplied by erosive processes occurring during the same period on the beaches and dune fronts located in areas further away from the jetties, which in many cases are heavily used. The aim of this paper was to analyse the accretion geometries and rates of beach–dune systems in several estuaries that drain into the Cantabrian coast and the subsequent erosion in the outer dune belt, testing a conceptual model formulated to explain the factors that determine the beach–dune response to human actions. The methodology applied can be exportable to other regions to facilitate the prediction of anthropic effects from harbour development and coastal management policies and the subsequent conservation of these environments.

Occurrence and speciation of arsenic and mercury in estuarine sediments affected by mining activities (Asturias, northern Spain)

Sediments contaminated by Hg and As from two historical mining areas have been deposited in the Nalón estuary (Asturias, northern Spain) since 1850. Total mercury (Hgtotal) concentrations in the sediments range from 0.20 μg g-1 to 1.33 μg g-1, most of it in the form of sulphides. Concentrations of methylmercury (303.20-865.40 pg g-1) are up to two orders of magnitude lower than the concentration of Hgtotal. Total As concentration (Astotal) is enriched compared to the background level for the area. The relative abundance of As(V) on As(III) in the sediments ranges from 97.6% to 100%, whereas inorganic Hg accounts for more than 99% of the total Hg. The occurrence of the most toxic species, inorganic As(III) and organic methylmercury, seem to be related to redox conditions together with the amounts of sulphur which act as natural barriers which inhibit the biological and chemical speciation processes. Despite the high amounts of Hg and As present in the sediments, their transference to the water column appear to be limited thus converting sediments in an effective sink of both elements. Special attention should be paid to potential variations of the environmental conditions which might increase the element mobility and exchange between sediments and the water column.

Holocene evolution of the Xagó dune field (Asturias, NW Spain) reconstructed by means of morphological mapping and ground penetrating radar surveys

Morphological mapping and ground penetrating radar (GPR) profiling were carried out in the Xagó aeolian dune field along the Asturias coast of NW Spain to reconstruct its Holocene evolution. Such data provide a much more accurate picture than can be inferred from surficial morphological studies alone. Three successive dune sequences were identified: an inner (climbing dunes), a middle (large transverse ridge and minor elongated dunes) and an outer dune field (foredune with lee-projection dunes and incipient foredune). A late Holocene sea-level fall is inferred from the relative position of the dunes together with a prograding tendency. Long intervals of stabilisation, during which each dune sequence was formed, are interspersed within the deposit. The GPR records also reveal a period of erosion in the southern middle field, which was followed by accretion. The results show that both progradational and erosional processes occurred during the Holocene evolution of the dune field, features that can be extended to other dune fields in similar settings at these latitudes. Stratigraphically, the Xagó dune field is an excellent example where internal reflectors reveal an erosion surface representing a transgressive or sea-level stillstand event that had previously remained undetected.

Aeolian Dune Fields in the Coasts of Asturias and Cantabria (Spain, Nw Iberian Peninsula)

Aeolian dune fields are relatively well represented along the cliff coast of Asturias and Cantabria (NW Iberian Peninsula) (Fig. 25.1; Tables 25.1 and 25.2). Siliciclastic sands are supplied by large rivers to their estuaries and coastal upwelling and nutrients from some estuaries contribute with the formation of carbonate sands, but inherited and currently generating bioclastic sands are important in several stretches; easterly winds produce upwelling in this coast and shelf mainly in spring and summer (Lavin et al. in The Sea 14, 24: 933–1001, 2004). Most of the Cantabria and Asturias dune fields were formed since the mid-Holocene (Flandrian transgression) once the sea level fell and the prograding processes seaward were favored. It is essential to know the evolutionary patterns from this early stage to those that have occurred since the middle of the 20th century as a result of mans intervention through dredging of the estuaries to which they belong. All dune fields of Asturias and Cantabria have been suffered a natural recession due sea level rise and the continuous surge event, increasingly more often. Policy, laws and management must go hand in hand for try to preserve in the best possible way this type of habitats of great importance for the coast.