Coastal geomorphology and evolution of Tierra del Fuego (Southern Argentina)

The northeastern Atlantic coast and the Beagle Channel are significant geomorphological areas of Tierra del Fuego (Southern Argentina). The northeastern Atlantic coast is located at the extra Andean lowlands (South- American Plate Domain). This coast line undergoes a macrotidal regime and is exposed to high energy waves and intense westerly winds. Extensive and wide beaches and littoral forms are composed of gravel and coarse sand. This zone was a free-ice area since 1,8 Ma B.P. Glacigenic deposits were re-worked by litoral processes that formed gravel beaches during sea level highstands of the. During the Holocene (i.e. approximately 5,000 years B.P.) gravel barriers plugged the inner estuaries of the palaeoembayments These barriers suggest a relative sea level fall of 0.214 m each 1,000 years, but a portion of this gradient could be due to wave dynamics since greater set-up of the storm waves enters the embayments. The growth of the northern gravel beach ridge plains and spits at the seaward flank of the embayments took place under limited sediment supply. The elongation of these littoral forms was triggered by erosion and sediment recycling at the seaward side (cannibalism), resulting in a significant landward retreat. Southward the gravel beach ridge plains underwent a regressive trend during the Holocene. They do not reveal either erosion, or sediment recycling, or significant landward retreat. The Beagle Channel connects the Pacific and Atlantic oceans. It is a 300 m depth basin separated from the Atlantic Ocean by a 30 m depth shallow sill. The Beagle Channel is located at the active seismotectonic setting of the Fuegian Andes (Scotia Plate Domain). It is a 5 km wide tectonic valley that was completely covered by ice during the Last Glaciation. After this period, glaciofluvial and glaciolacustrine environments developed in the basin. The Beagle valley was rapidly flooded by the sea immediately after the Younger Dryas, 11,000 year B.P. It undergoes a micro tidal range regime and shows a rugged, rocky shoreline where pocket gravel beaches develop in the embayments. Holocene raised beaches can be recognized in many places along the channel and their elevations vary considerably, reaching maximum elevations of 10 m above the present counterpart at ages of 6,000 years B.P. The estimated average tectonic uplift for this period is 1.5 to 2.0 mm/year

A Global Classification of Astronomical Tide Asymmetry and Periodicity Using Statistical and Cluster Analysis

ABSTRACT: Tidal asymmetry plays a key role in the behavior of estuaries. Positive and negative asymmetries are associated with flood- and ebb-dominated estuaries, respectively. Asymmetry arises from both the interaction among the main tidal constituents and the harmonics generated when tide propagates in shallow waters. Most previous research focuses on the deformation of the tide within estuaries; however, ocean tide may show asymmetry at the estuary entrance, which implies that the boundary condition is already deformed. This fact has important implications for tide propagation, estuarine transport processes, and flow exchanges between estuaries and open oceans. In this study, the global astronomical tide is classified according to its asymmetry and periodicity. The objective is to provide a guiding framework of representative astronomical tide types (ATtypes) on a worldwide scale to be used as a reference for further research on the transport of substances in estuaries. The applied methodology is based on the use of the TPXO9-atlas global barotropic tidal solution and detailed statistical analysis. Probability density functions of the tidal elevation time derivative and the tidal form factor were extracted from TPXO9-atlas with a spatial resolution ranging from 1/6° to 1/30°. The K-means algorithm was applied to these parameters, and 25 representative ATtypes were identified. The classification was validated with 757 worldwide tide gauge records. The results show that 11.3% of coastal areas show negative asymmetries, 11.3% positive asymmetries, while symmetric tides dominate 77.4% of coastal areas. In these areas, estuaries can show asymmetries exclusively dependent on overtides and compound tides generated during inland propagation without being externally conditione

Gravelly cuspate forelands on the Atlantic coast of Patagonia. Examples of the Bustamante and Dungeness Points, (Argentina and Chile)

In the Patagonia region the eustatic sea rise was produced 20000 years BP and some glacial valleys such as Magellan straight and rio Gallegos estuary were flooded. Tills were reworked by tides and waves, and several cuspate forelands (Bustamante and Dungeness points) were developed as a consequence. Although the growing patterns of these two points are different, It is possible to stablish some similarities about the accretion processes. At first the gravels can be carried from the cliffs until the points by continental drift currents along the atlantic coast. Secondly, some events which can carry gravels from the atlantic ocean to the coast occurred. The Dungeness point was produced mainly as a consequence of the continental drift currents. On the other hand, the Bustamante point was originated by the marine currents from the ocean to the continen

Efecto amplificador del suelo en la exposición al peligro sísmico de Tolhuin, Tierra del Fuego, Argentina

The island of Tierra del Fuego (Argentina-Chile) lies in aregion of intense seismic activity due to the interaction of theAntarctica, Scotia and South American tectonic plates. Twoseismotectonic zones in this region: the subduction trench insouthernmost Chile and the Magallanes-Fagnano fault, that crosses the island from east to west, represent a seismic hazard for the island population. Focusing on the Argentine sector of Tierra del Fuego, however, the greater threat comes from the Magallanes-Fagnano fault, which has generated seismic events in historical times of magnitude M=8. Tolhuin, a small population of 3000 inhabitants undergoing fast growth, is located 1 km from the trace of the Magallanes-Fagnano fault. Buildings in Tolhuin largely have not had seismic safety controls required by the INPRES (the Argentine seismic building code regulator). In addition, the urbanization of Tolhuin rests on a thick package of Quaternary glacigenic sediments with the potential for amplifying seismic vibrations by a factor of more than 2, judging from a simulation with EERA (Equivalent-linear Earthquake Analyses). Applying the Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disasters (RADIUS) methodology, supported by the United Nations, this study analyses the seismic vulnerability of constructions in Tolhuin under the effect of a Maximum Considered Earthquake of magnitude M=8.0. The results show the importance of considering the probable local amplification through site effects. This study constitutes a first effort to provide the Argentine province of Tierra del Fuego with cartographic and conceptual tools useful in planning urban growth taking into consideration seismic hazard.La Isla Grande de Tierra del Fuego (Argentina-Chile) está situada en un entorno de intensa actividad sísmica merced a lainteracción de las placas tectónicas Antártica, Scotia y Sudamericana. Dos zonas sismotectónicas en esta región: la fosa desubducción en el extremo austral de Chile y la falla Magallanes-Fagnano, que cruza la isla de este a oeste, representan unaamenaza sísmica para la población local. Considerando únicamente el sector argentino de la Tierra del Fuego, sin embargo,la mayor amenaza proviene de la falla Magallanes-Fagnano, la cual ha generado eventos sísmicos de magnitud M=8 entiempos históricos. Tolhuin, una pequeña población de 3000 habitantes en rápido crecimiento, está a 1 km de la traza deesta falla. Las construcciones de Tolhuin en gran parte no han tenido el control de sismorresistencia que requiere el INPRES(Instituto Nacional de Prevención Sísmica). Por otra parte, la urbanización de Tolhuin apoya sobre un espeso paquete desedimentos glacigénicos del Cuaternario cuyas características geotécnicas sugieren que puede amplificar a más del doble unavibración sísmica, de acuerdo a una simulación con EERA (Equivalent-linear Earthquake Analyses). Aplicando lametodología Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disasters (RADIUS) propiciada por lasNaciones Unidas, este estudio analiza la vulnerabilidad edilicia de Tolhuin ante un Terremoto Máximo Considerado deM=8,0. Los resultados muestran la importancia de tomar en cuenta la probable amplificación local por el efecto suelo. Elpresente trabajo constituye un primer esfuerzo concertado para dotar a la provincia argentina de Tierra del Fuego deherramientas cartográficas y conceptuales útiles para planificar el crecimiento urbano tomando en cuenta la prevenciónsísmica

Contribution of Wave Setup to Projected Coastal Sea Level Changes

International audienceAlong open coasts, wind waves are a key driver of coastal changes and can be major contributors to coastal hazards. Wind wave characteristics are projected to change in response to climate change, notably due to changes in atmospheric circulation patterns and the associated surface winds. Here, a first-order estimate of projected 20-yr mean wave setup changes, excluding extreme events and subannual variability, is provided for sandy beaches along most of the world's coastline over the middle and end of the 21st century. Calculations are based on an ensemble of wave model projections under the representative concentration pathways (RCP) 8.5 and on empirical formulations for wave setup. Projected wave setup changes are compared to other contributors currently accounted for in regional sea level projections to extend existing projections of 21st century coastal sea level changes. Projected wave setup changes exhibit a clear spatial heterogeneity and mostly average out at global scale. However, at regional or local scale, wave setup changes are a small yet nonnegligible contributor to total coastal sea level 20-yr mean changes (which include global mean sea level rise, GMSLR) over the middle and end of the 21st century. Wave setup can be a substantial contributor to local departures of coastal sea level changes from GMSLR. Wave setup changes should therefore be included in projections of regional patterns of coastal sea level changes. The reported long-term changes in wave setup also advocate for the inclusion of nonstationary wave contributions to projected regional patterns of coastal sea level changes, including for studies on extreme events

Kelp geese (Chloephaga hybrida) and Flightless steamer ducks (Tachyeres pteneres) in the Beagle Channel: the importance of islands in providing safe nesting habitat

We describe nest-site characteristics and studied breeding habitat use of Kelp geese (Chloephaga hybrida) and Flightless Steamer ducks (Tachyeres pteneres) along 137km of coastline on the northern shore of the Beagle Channel, Argentina, and 87 km of island coastline. Also, we examined the importance of vegetation cover, predation and tourism on the distribution of nests among islands. We found all nests only on islands and islets. Nesting sites for both species were strongly associated with higher proportions of high vegetation cover (shrubs), and for Kelp geese they were also associated to the absence of terrestrial predators. Tourist presence on islands was not associated to the presence of nest for neither species. The northern coasts of the Beagle Channel and the islands and islets along the channel have similar habitat types. However, the islands and islets are relatively inaccessible to mammalian terrestrial predators compared to the coast of the channel were terrestrial predators are frequently recorded. Therefore, islands and islets seem to provide a relatively safe nesting habitat for Kelp geese and Flightless Steamer ducks by offering refuge mainly from ground predators. Additionally, habitat changes caused by increased human disturbance along the northern shore of the Beagle Channel may also explain the presence of nests only on islands and islets, though further studies are needed to assess these effects. This study provides new information on the breeding habitat and nesting sites of Flightless Steamer ducks and Kelp geese in the Beagle Channel, which in the future may contribute to the identification of priority breeding sites, and habitats and habitat features to protect. Also, it highlights the importance of islands and islets of the Beagle Channel as a safe breeding refuge for these two ground nesting seabirds.Fil: Liljesthrom, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Schiavini, Adrian Carlos Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Saenz Samaniego, Ricardo Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Fasola, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Raya Rey, Andrea Nélida. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin