Abstract

ARROYO-SOLORZANO, Mario; QUESADA-ROMAN, Adolfo  and  VARGAS-BOLANOS, Christian. Morphotectonic-volcanic units of the northwest sector of Poás volcano, Costa Rica. Invest. Geog [online]. 2021, n.105, e60279.  Epub Nov 01, 2021. ISSN 2448-7279.  https://doi.org/10.14350/rig.60279.

The tectonic and volcanic dynamics of Costa Rica respond mainly to the interaction of the Cocos and Caribbean plates (and the Panama Microplate) near a triple junction where these interact with the Nazca Plate. This work used Lidar images from the Northwest sector of the Poás Volcano generated after the 2009 Cinchona earthquake (Mw 6.2) and supplementary inputs to analyze the morphotectonic traits and propose morphotectonicvolcanic units (UMTV) on a 1:25.000 scale. This sector has been defined as the area of interest because it is the least studied of the Poás Volcano and covers an important part of the national park protection zone. UMTVs were defined from the analysis of the morphometric elements of relief, lithologic conditions, and morphostructural expressions of relief structures. Thus, this study represents an initial step in determining this type of morphostructural relationships of relief in Costa Rica, which can be replicated as a tool in the evaluation of natural hazards in other countries with similar characteristics.

Based on previous studies in the area as and using remote sensors (Lidar, radar images, and aerial photographs), criteria were combined including identification and interpretation of tectonic or volcanic structures, altitudinal range, geology and origin of relief forms, slope, seismicity, and guidelines and interpretation of patterns in the hydrographic network. Methodological processes were grouped as follows: a) development of the elevation and shading digital model through processing in ArcMap 10.5 for use in morphometric analyses and identification of tectonic structures; b) geomorphological mapping, analysis of relief morphoelements and litho-stratigraphic and seismicity relationships; c) analysis of altimetric ranges and slopes; d) analysis of structural patterns according to the hydrographic network and its morphometry (dissection depth and density); and e) interpretation of radar images and aerial photographs from available sources.

Ten UMTVs were defined that characterize the relief resulting from the evolution of the Poás Volcano northwest sector, based on the relationship between geological structures, altitudinal ranges, morphometric parameters, and relief forms. Besides, these units evidence the importance of neotectonic activity in the formation and differentiation of relief and are a major input in the study of relief forms and natural hazards. Therefore, it is a practical tool for disaster risk mitigation by identifying areas susceptible to seismic and volcanic activity, and those related to extreme hydrometeorological phenomena, such as floods and landslides, under different vulnerability scenarios and multiple-hazard contexts. The most vulnerable UMTVs are ancient, secondary, or current volcanic cones, areas with major faults or fracturing on moderate-to-high slopes and with tectonicstructural control, corresponding to conic and structural volcanic UMTVs or with active-fault tectonics in areas of steep slopes (> 15°). These units display characteristics such as many rivers running through canyons, radial, semi-radial or sub-parallel drainage patterns associated with volcanic geomorphologies, and denudation aspects resulting from ancient landslides.

The greatest advantage of the proposed method is the use of easily accessible morphometric parameters from level curves and the generation of its hydrographic network, which can be replicated in similar territories or contexts with available information on basic local geology and tectonics. A limitation of the modeling method is the scale of some of the source data, as studies of this type require either having of producing accurate maps (at least 1:25.000 scale). The definition of UMTVs represents an initial input for the evaluation of natural hazards, being a valuable tool for land-use planning and risk management, with potential for replication in zones sharing characteristics similar to those of the study area, in volcanic environments and tropical climates.

Keywords : Morphotectonics; volcanic geomorphology; Poas Volcano; morphometric parameters; relief.

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