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- Recent Macaronesian kinematics from GNSS ground displacement analysisPublication . Barbero, Ignacio; Torrecillas, Cristina; Paez, Raul; Prates, Gonçalo; Berrocoso, ManuelMacaronesia is a complex oceanic region spanning three tectonic plates in the northeast Atlantic ocean. It is composed of four archipelagos, widely distributed and limited to the east by the Iberian Peninsula and north-western coast of Africa. This study aims to clarify recent Macaronesian kinematics from 19 GNSS stations located on the four archipelagos and the Iberian and African coastlines. The analysis is based on nearly 15 years of common data acquisition and aimed to detect new effects of intraplate tectonics or similar local/regional events consistent with calculated ground displacements. Evaluating the GNSS stations residual velocities relative to those expected from the NNR-MORVEL56 model, higher residuals were found at continental coastal stations (Africa) than at oceanic ones (Canaries and Madeira). From the computed strain rate map, the possible existence of a shear zone connecting the Gloria and Transmoroccan fault systems, already mentioned by other authors, was depicted. Cluster statistical analysis of the horizontal residual velocities helped to identify tectonic boundaries in Macaronesia and four groups of analogous intraplate residual velocities within this region. Three of four groups were identified in the Azores, highlighting the African-Nubian-Eurasian diffuse plate boundary in this region. Furthermore, in the Canary Islands, two distinct kinematic behaviours were detected, possibly due to the activity along a previously detected tectonic fault between Tenerife and Gran Canaria, where some stations have similar intraplate residuals to those at Madeira and Cape Verde stations, while others have similar intraplate residuals to those of continental stations. Finally, all stations on oceanic crust, except Cape Verde, present recent ground subsidence which may be attributed to isostatic adjustment.
- Shoreline change rates and land to sea sediment and soil organic carbon transfer in eastern Parry Peninsula from 1965 to 2020 (Amundsen Gulf, Canada)Publication . Tanguy, Rodrigue; Whalen, Dustin; Prates, Gonçalo; Vieira, GonçaloAs the Arctic is warming, permafrost coasts are eroding faster, threatening coastal communities, habitats, and altering sediment and nutrient budgets. The western Canadian Arctic is eroding at a rapid pace; however, little is known on changes occurring in the Amundsen Gulf area. This study was conducted in the eastern coast of Parry Peninsula, a neglected rock dominated coastal area. We used orthorectified aerial photos of 1965 and 1993 and very high-resolution satellite imagery of 2020 to manually delineate the shoreline according to backshore and foreshore centered approaches. Shoreline change rates were calculated and sediment and organic carbon transfer from land to sea estimated using digital elevation model, the Northern Circumpolar Soil Carbon Database, and ground ice content. The results show a mean erosion rate of 0.12 m/yr for the backshore zone and 0.16 m/yr for the foreshore zone, with increasing erosion in the Paulatuk Peninsula in recent decades. The average sediment transfer from land to sea was 20 m3/m/yr and the soil organic carbon (SOC) flux was 7 kg C/m/yr. We highlight the importance of using the cliff-top as shoreline reference to accurately estimate sediment and SOC transfers, an approach neglected in automatic shoreline delineation techniques based on remote sensing imagery using the waterline.
- Territory and drystone walls. Comparative of case studies in central and southern PortugalPublication . Marçal Gonçalves, Marta; Prates, Gonçalo; Pérez-Cano, María Teresa; Rosendahl, Stefan; I. Lombillo; H. Blanco; Y. BoffillSince becoming settled, Man had the need to shape the territory in his benefit, gaining ground for agricultural activity. Drystone walls were the way found to overcome sharp slopes. The way these walls are arranged in the territory is not random, as it may seem at first glance: they are disposed in the best way to facilitate the agricultural activity, taking into account the natural factors of the territory where they are located, such as orography, climate or geology. Taking as study cases two regions in Portugal under slightly different climate regimes, one located in the Algarvian Barrocal and the other located in the Center, we intend to compare and advance with explanations as to the way drystone walls are disposed and their relation to the territory. To achieve the objectives bibliographical and photographic studies, as well as interviews with the inhabitants of these areas, and cartographic and field surveys were carried out. Whereas the purpose, materials and construction characteristics were achieved by the previous, their disposition and relationship with the orography were carried out by the latest. Particularly, field surveys were made by digital stereophotogrammetry applied to several overlapping nadiral photographic images from different perspectives acquired by an unmanned aerial vehicle along its flying pathways that allowed for very high-resolution geographic data. Where such surveys were not made, cartographic data were used instead. Through the dissemination of such vernacular heritage, it becomes valued and known. In this way, people will attribute cultural and patrimonial value, protecting it, especially the local population that tends not to attribute any value to this “minor” heritage, contributing to its disappearance. There are still not much works about this subject in the areas analyzed here, so this paper has an added value, in order to disseminate and create added value to these kind of heritage.
- Silves bridge geometric model via structure-from-motion: tool for heritage digital catalogsPublication . Prates, Gonçalo; Marçal Gonçalves, Marta; Lopes, Ana; Laranja, RobertoThe old bridge in Silves, Portugal, has five perfectly formed arches extending over the Arade river with about 76 meters long built of local materials. In the 14th century this structure was rebuilt on the location of a previous structure built when Silves was the Moorish capital between the 8th and 13th centuries occupation of the Algarve. Though a Roman road might have crossed this area, there is no medieval descriptions mentioning a bridge in Silves, still it is also known as the Roman bridge.After interventions in the 14th, 17th, 18th and 20th centuries, the bridge was classified as monument of public interest and became pedestrian-only and frequently evaluated for its risk of collapse. Stereo-photogrammetry is a recognized surface reconstruction tool applied for almost one century, where from several overlapping images of the surface a 3D model can be obtained. Contrasting with classical stereo-photogrammetry, Structure-from-Motion (SfM) is a nearly automated compilation of digital imagery processing strategies that solve for camera position and surface geometry using matching features identified in several images from diverse perspectives and preferably with high degree of overlap. Together with ongoing increase in computer power, SfM allowed digital stereophotogrammetry to be operative for close-range, high-resolution and non-metric overlapping digital images, and cost-effective. Applying these nearly automated strategies to digital images of the old bridge in Silves taken from the surrounding grounds, a dense point-cloud was computed providing its complete digital model allowing accurate measurements and materials visual identification, key elements for heritage digital catalogs and historical building information models.
- Deception Island 1967–1970 volcano eruptions from historical aerial frames and satellite imagery (Antarctic Peninsula)Publication . Prates, Gonçalo; Torrecillas, Cristina; Berrocoso, Manuel; Goyanes, Gabriel; Vieira, GonçaloAerial frames and satellite imagery are widely recognized data sources from which to produce maps. For volcanoes, maps enable the quantification of erupted ash and the destruction caused. The last eruptive sequence on Deception Island was endured from 1967 to 1970. Analogue maps were produced via classical photogrammetric methods with a high degree of human intervention mainly to analyse the volcanic-centres areas only. However, historical aerial frames cover the whole of Deception Island. Structure from motion photogrammetry, a near-automated compilation of digital image processing strategies, minimizes the degree of human intervention to produce orthographic mosaics and digital elevation models from digital aerial frames. Orthographic mosaics were produced from historical aerial frames of 1956 and 1968, and a Kompsat-3 image of 2020. Their shared rootmean-square deviation was 1.8 m and 1.7 m in easting and northing, respectively, at ground control points measured with phase-differential global navigation satellite systems. The digital elevation models were processed with a root-mean-square deviation of 2.3 m and 3.6 m from 1956 and 1968 aerial frames, respectively. As the first application, erupted ashfall and the subsequent destruction, mainly at the former Chilean and British bases, were identified, and the volume of erupted ash was assessed to be over 0.16 km3 within the area mapped by these new digital cartographic products.
- Evaluation and modelling of the coastal geomorphological changes of deception island since the 1970 eruption and Its involvement in research activityPublication . Torrecillas, Cristina; Zarzuelo, Carmen; de la Fuente, Jorge; Jigena-Antelo, Bismarck; Prates, GonçaloDeception Island is an active volcano with a submerged caldera open to the sea called Port Foster. Several post-caldera-collapsed volcanic events, as well as hydrodynamics, have changed its inner coastline, shaping new volcanic deposits. A hydrodynamic model is presented to predict accretion and erosion trends in this bay, which could have an impact on the mobility of researchers and tourists. New historical orthophotos and spatio-temporal differences between digital elevation and bathymetric models were used for validation purposes. The model reveals that the south-facing coast is more susceptible to erosion, while the east- or west-facing coast experiences sedimentation. A visual study for the periods 1970–2003 and 2003–2020 in Port Foster obtained similar annual erosion/accretion lineal rates (0.3–2 m/year) in the areas not affected by the last eruptive period, as well as increases of 0.023 km2/year and 0.028 km2/year of the inner bay and coastal sedimentation rates of 0.007 km2/year and 0.002 km2/year, respectively. Only part of the significant total volume loss is received within the bay, including its own erosion, and accumulates on the bay bottom. This is largely because the volume input is composed of snow, and it is also due to the transfer of material outside to balance the figures.
- Surface displacement of Hurd Rock glacier from 1956 to 2019 from historical aerial frames and satellite imagery (Livingston Island, Antarctic Peninsula)Publication . Prates, Gonçalo; Vieira, GonçaloIn the second half of the 20th century, the western Antarctic Peninsula recorded the highest mean annual air temperature rise in the Antarctic. The South Shetland Islands are located about 100 km northwest of the Antarctic Peninsula. The mean annual air temperature at sea level in this Maritime Antarctic region is close to −2 °C and, therefore, very sensitive to permafrost degradation following atmospheric warming. Among geomorphological indicators of permafrost are rock glaciers found below steep slopes as a consequence of permafrost creep, but with surficial movement also generated by solifluction and shallow landslides of rock debris and finer sediments. Rock glacier surface velocity is a new essential climate variable parameter by the Global Climate Observing System, and its historical analysis allows insight into past permafrost behavior. Recovery of 1950s aerial image stereo-pairs and structure-from-motion processing, together with the analysis of QuickBird 2007 and Pleiades 2019 high-resolution satellite imagery, allowed inferring displacements of the Hurd rock glacier using compression ridge-and-furrow morphology analysis over 60 years. Displacements measured on the rock glacier surface from 1956 until 2019 were from 7.5 m to 22.5 m and surface velocity of 12 cm/year to 36 cm/year, measured on orthographic images, with combined deviation root-mean-square of 2.5 m and 2.4 m in easting and northing. The inferred surface velocity also provides a baseline reference to assess today’s displacements. The results show patterns of the Hurd rock glacier displacement velocity, which are analogous to those reported within the last decade, without being possible to assess any displacement acceleration.
- The time lag between deformation process and seismic activity in El Hierro Island during the eruptive process (2011–2014): a functional phased approachPublication . Pérez-Plaza, Sonia; Berrocoso, Manuel; Rosado, Belén; Prates, Gonçalo; Fernández-Palacín, FernandoOn 10 October 2011, a submarine eruption occurred in El Hierro island. Thus, the eruptive process in the Canary islands was reactivated after 40 years of inactivity. The main objective of this work is to evaluate, using Functional Data Analysis, how the surface deformation phenomenon explains the seismic–volcanic activity in the island. The GNSS-GPS data are from the FRON (GRAFCAN) station, located in Frontera. These data measure, each 4 h, the distance between the FRON station and the reference station LPAL (La Palma island) from August, 2010 to December, 2013. In this study a functional correlation measure is employed to establish the relation between the deformation curve and the curve of cumulative energy released. The period of time analysed has been divided into four phases to avoid the mix of phenomena. For each phase, the correlation measure and the time lag between deformation curve and the curve of cumulative energy released have been estimated. These values show a strong relation between these curves. With respect to time lag period, the only signifcant lag, of about 1 month, occurred in Phase 1, which was after a long period without seismic activity. The later phases had very short, insignifcant, lags. After a long period without seismic and volcanic activity in El Hierro island, the time lag between the deformation process and the beginning of the seismic activity takes approximately 1 month. In a similar situation a method to predict in real time the beginning of the seismic activity is proposed. This method, based on the changes produced in the derivative curves when there is a rapid descent in the deformation curve, could activate a warning system approximately 13 days before the beginning of seismicity.