Germán Flor

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.

Integrated assessment and evaluation of the coastal environment of the province of vizcaya, bay of Biscay, Spain

A methodology for the quick, overall assessment of the capability of different parts of a coastal environment to be used for human activities is described. The methodology is based on the elaboration of a series of thematic maps (geologic, biologic, and dynamic, e.g., currents, features) for the three “environmental systems” that were defined (marine, estuarine, and emerged coastline). The thematic maps are combined to define “homogeneous units” and these are then evaluated for the attractiveness and impact corresponding to a series of selected activities. Alternatively, the mapped features can be evaluated directly for certain systems, without defining homogeneous units. The combination of attractiveness and impact is used to obtain the relative capability of each unit for each activity, thus establishing the activities that are most advisable in each case.

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.

Alluvial systems in the northwestern part of the Duero Basin (Spain)

Abstract In the Miocene sediments of the northwestern corner of the Duero Basin (Spain) several synchronous depositional systems can be distinguished by their lithofacies, lithologic composition of the conglomerates, heavy mineral assemblages and textural characteristics of the sandstones. A first set of systems comes from the north and is formed by alluvial fans, either originating from mass flow processes or deposited by braided streams; this contrasting origin is attributed to the petrographically differing nature of the parent rocks since a striking change of climate can not be invoked within an area as small as this. The second set, coming from the west, is made up of deposits of braided rivers, strongly controlled by paleovalleys. One of them passes downstream into a high sinuosity pattern and forms the trunk river for all the other rivers. Three stages can be distinguished in the depositional history of these systems. From these the expansive character of the basin is inferred.

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.