Side scan sonar image and geologic interpretation of the Ría de Pontevedra seafloor (Galicia, NW Spain)

Soledad García-Gil,Federico Vilas,Ruth Durán

doi:10.3989/scimar.2000.64n4393

Soledad García-Gil, Federico Vilas + Show 1 more

Open Access

https://doi.org/10.3989/scimar.2000.64n4393

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Journal: Scientia Marina	Publication Date: Dec 30, 2000
Citations: 17	License type: cc-by

Affiliation: Universidade de Vigo

Abstract

High-resolution side scan sonar has been used for mapping the seafloor of the Ria de Pontevedra. Four backscatter patterns have been mapped within the Ria: (1) Pattern with isolated reflections, correlated with granite and metamorphic outcrops and located close to the coastal prominence and Ons and Onza Islands. (2) Pattern of strong reflectivity usually located around the basement outcrops and near the coastline and produced by coarse-grained sediment. (3) Pattern of weak backscatter is correlated with fine sand to mud and comprising large areas in the central and deep part of the Ria, where the bottom currents are weak. It is generally featureless, except where pockmarks and anthropogenic features are present. (4) Patches of strong and weak backscatter are located in the boundary between coarse and fine-grained sediments and they are due to the effect of strong bottom currents. The presence of megaripples associated to both patterns of strong reflectivity and sedimentary patches indicate bedload transport of sediment during high energy conditions (storms). Side scan sonar records and supplementary bathymetry, bottom samples and hydrodynamic data reveal that the distribution of seafloor sediment is strongly related to oceanographic processes and the particular morphology and topography of the Ria.

Highlights

AND PREVIOUS WORKThe first detailed maps of the Ría de Pontevedra deal with textural distribution of seafloor sediments in terms of grain-sized ternary diagrams, carbonated and organic matter contents, based on regularly spaced bottom samples (Vilas et al, 1996)
In the Ría de Pontevedra, this pattern is characterised by a strong surface return and high bathymetric relief and fractures resulting in areas with acoustic shadows (Fig. 5)
From the interpretation of the sonograph mosaic from the Ría de Pontevedra seafloor a spatial distribution of the four different patterns described above can be recognised

Summary

Introduction

AND PREVIOUS WORKThe first detailed maps of the Ría de Pontevedra deal with textural distribution of seafloor sediments in terms of grain-sized ternary diagrams, carbonated and organic matter contents, based on regularly spaced bottom samples (Vilas et al, 1996). (2) Pattern of strong reflectivity usually located around the basement outcrops and near the coastline and produced by coarse-grained sediment. (4) Patches of strong and weak backscatter are located in the boundary between coarse and fine-grained sediments and they are due to the effect of strong bottom currents.

Results

Conclusion