Caracterización de médanos parabólicos de la región pampeana oriental, centro oeste de la provincia de Buenos Aires (Argentina)
Characterization of parabolic dunes of the oriental pampean region, west center of the province of Buenos Aires (Argentina)
Fecha
2018Autor
Contreras, Félix Ignacio
Mavo Mastretta, Gian Marco
Perillo, Gerardo Miguel E.
Piccolo, María Cintia
Metadatos
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La región pampeana, especialmente la provincia de Buenos Aires, se caracteriza por
la presencia de paisajes eólicos que, si bien responden a eventos producidos en el
Cuaternario Superior, en la actualidad son reactivados por la actividad agropecuaria.
El objetivo de este trabajo se centra en la detección y delimitación de un campo de
médanos parabólicos parcialmente reactivados, ubicados en el centro oeste de dicha
provincia, que si bien han sido mencionados en la literatura, no han sido objeto
de estudio detallado. Mediante la generación de un Modelo Digital de Elevaciones
(MDE) a partir de imágenes SRTM (Shuttle Radar Topography Mission) se ha detec-
tado un campo con un total de 254 médanos parabólicos que ocupan 20.200 km2,
ubicados entre los 120 y 90 msnm. Los mismos presentan una dirección general
SW-NE, con anchos que varían entre 2 y 5 km y alturas entre 2 y 6 m. Aplicando
la herramienta Distancia Vertical al Curso (Vertical Distance to Channel Network,
VDCN) del Software SAGA GIS 2.1.2 y una clasificación automática no supervisada
en ArcGIS 10.1, se lograron discriminar los médanos de la planicie circundante. A
partir de muestras de sedimento de un médano testigo ubicado en la localidad de
30 de Agosto (Buenos Aires), se establecieron claras diferencias en la granulometría
en distintos sectores del mismo. La ubicación de estos médanos es clave en la confi-
guración del escurrimiento y, en consecuencia, este paisaje arenoso tiene un rol im-
portante en la configuración del espacio del área de estudio ya que se forman lagu-
nas intermedanales someras cuyo desarrollo depende de las precipitaciones locales. The Pampean region is a fertile and extensive availability of water resources (Aliaga et al., 2017).
The Buenos Aires Province is especially charac-
terized by the presence of aeolian landscapes that,
even though they were developed in the past, they
are currently being reactivated by agricultural
activities. The antecedents indicate different dune
morphologies within the province territory, mainly
associated with sediment availability and wind
direction (Iriondo and Kröhling, 1995; Isla et al.,
2010; Zárate and Tripaldi 2012).
The focus of this work is the detection, delimi-
tation and characterization of a parabolic dune field
located in the Middle West of the Buenos Aires
Province (Fig. 1) for which no precedent has been
found. Likewise, we also establish the relationship
between the parabolic dunes and the distribution
and evolution of the interdune shallow lakes asso-
ciated with them. Through the generation of a
Digital Elevation Model (DEM) from Shuttle Radar
Topography Mission (SRTM) images, a field with 254
parabolic dunes that covers 20,200 km2 was detected
(Fig. 1). It is located between 120 and 90 m above
mean sea level, with SW-NE general orientation;
widths between 2 and 5 km, and heights between 2
and 6 m. The Vertical Distance to Channel Network
(VDCN) tool of the SAGA GIS 2.1.2 software was also
employed (Fig. 3) and, additionally, an automatic
unsupervised classification using ArcGIS 10.1 was
carried out in order to discriminate the dunes from
the surrounding plain.
Grain size analysis were carried out in both dune
and interdune areas. The analysis was performed
employing a Mastersizer 2000 Laser Particle Ana-
lyzer, whose results were represented with the
GRADISTAT v8 software. The results demonstrate
clear differences between the interdune areas, having
very fine materials, with respect to those obtained
within the dune area, which varied depending on
the sector and the depth of the sample, establishing
differences in the various dune sectors. For example,
an increase in finer materials in depth. Also revealed
that they are fine sand dunes, but the bimodal
curve obtained with fine materials suggests that its
sediments respond to different climatic periods. The
progressive increase of fine material inside the dune
shows that there is a material redistribution.
Simultaneously with the sampling, a flight with
an unmanned aerial vehicle (UAV) was made, that
allowed generating a set of videos and 360o pano-
ramic photographs, later used in the generation plain of Argentina. It has an extension of 613,532
km2 located within the temperate region, being also
adjacent to the Atlantic Ocean. The latter generates
low daily and annual thermal amplitudes than in
other regions in similar latitudes. In addition, the
region is characterized by the occurrence of long
periods of floods and drought, which affect the of orthomosaics, dense point cloud and a three-
dimensional model (Fig. 6) using the SFM (Structure
From Motion) method (Genchi et al., 2015). The
method is based on sequential image acquisition,
with a high overlap degree, and founded in the
correlation of points identified in different images
(Fernández and Gutiérrez, 2016). The images were
optimized (USGS, 2016) obtaining a higher accuracy
in the photograph parameters by correcting the
distortions caused by the camera lens. Besides the
method helps to improve the general model, whose
scene geometry, camera location and orientation
of the photographs were taken automatically but
derived from the appropriate superposition (> 60 %).
According to its morphology, the dunes were
categorized into three classes (Table 1), being the
symmetric dunes the most common, followed by
the asymmetric dunes and, finally, those of lateral
coalescence that, despite being inferior in quantity,
possess greater spatial development, that is, have
longer crestal lengths (Fig. 7). Bordering the margins
of the dune field to the north, east and south we
observed the typical longitudinal dunes characteristic
of this Pampean region sector. According to Bagnold
(1941), it is possible that some simple semilunar
forms are deformed in longitudinal features when
moving in areas with variable wind directions.
The results demonstrate that there are 254 crests
distributed in the area, with a density of 0.01 dunes/
km2, many of them are segmented due to natural
process through the presence of small shallow lakes
and temporary depressions whose approximate
depth is 1 m (Fig. 4 and 5), but also increased by
the removal of soils as a result of agricultural
activity. The shallow lakes disposition allows in-
ferring that, in presence of abundant rainfall; they
can be connected and/or overflowed, flooding the
surrounding areas. The location of these dunes is
crucial in the spatial surface runoff configuration
and, in consequence, this sandy landscape has an
important role in the spatial configuration of the
area generating risk conditions to both the local
population and agricultural production.
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