Application of GPR in the Study of a Modern Alluvial Megafan: The Case of the Taquari River in Pantanal Wetland, West-Central Brazil

Porsani, Jorge Luís; Assine, Mário Luís; Moutinho, Leandro

doi:10.1007/s11220-005-0008-x

Cited by 13 publications

(5 citation statements)

References 9 publications

(14 reference statements)

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“…The margins of the saline lakes are surrounded by the sandy low-relief cordilheiras , which are commonly covered in wooded savanna vegetation (Fig. 3) (Pott et al, 2011). The lakes are interspersed among seasonal floodwater courses ( vazantes ) and permanent channels ( corixos ) (Fig.…”

Section: Study Areamentioning

confidence: 99%

Holocene stratigraphic evolution of saline lakes in Nhecolândia, southern Pantanal wetlands (Brazil)

et al. 2017

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Nhecolândia is a fossil lobe of the Taquari River megafan and a prominent geomorphic subunit of the Pantanal wetlands because of the presence of >10,000 small lakes. We investigated the stratigraphic records of three saline lakes from Nhecolândia to explore their potential as Quaternary hydroclimate archives. Radiocarbon data indicate that accumulation at two lakes was approximately continuous in the late Holocene, and chemostratigraphic variability suggests sensitivity to environmental change with multicentennial resolution. A basal sandy unit and an upper muddy unit comprise the shallow stratigraphy of each lake. A pronounced change in depositional environment from freshwater wetlands to saline lakes at ~3300–3200 cal yr BP best explains the lithofacies transition. Ephemeral freshwater wetlands formed on the abandoned megafan lobe, which was molded by deflation in the arid early Holocene. Wind-scouring of the megafan lobe generated topographically closed depressions with complex marginal sand ridges, which allowed permanent lakes to evolve when rainfall increased in the late Holocene. The lakes became highly saline and alkaline after ~910 cal yr BP, which influences biogeochemistry and aquatic ecology. The results hold implications for understanding the response of the southern Pantanal to climate change, as well as the development of pans in tropical megafan settings.

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Section: Study Areamentioning

confidence: 99%

Holocene stratigraphic evolution of saline lakes in Nhecolândia, southern Pantanal wetlands (Brazil)

et al. 2017

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“…Another factor associated with the sandy subsurface is that overbank flows in this area are capable of scouring deep floodplain channels, which provide efficient avulsion pathways when connected to the parent channel by crevassing (e.g. Porsani et al, 2005). Ultimately, the middle fan avulsion can be attributed to the upstream control of (variable) sandy sediment input into the system, leading to aggradation and favourable subsurface conditions.…”

Section: Summary Of Causesmentioning

confidence: 99%

“…Here, we present an analysis of avulsions on the Taquari megafan, Pantanal basin, south‐western Brazil (Figure A). Recent crevassing and avulsion activity on the Taquari megafan (Padovani et al ., ; Assine, ; Porsani et al ., ) concentrates in two areas: (1) on the middle fan near the apex of the presently active fan‐lobe (e.g. Figure ), immediately downstream of a reach of the Taquari that is incised into the upper fan surface, (2) on the lower fan, in a ~50‐km‐long reach upstream of the edge of the fan.…”

Section: Introductionmentioning

confidence: 99%

Upstream and downstream controls of recent avulsions on the Taquari megafan, Pantanal, south‐western Brazil

Makaske

Maathuis

Padovani

et al. 2012

Earth Surf Processes Landf

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Avulsion, the natural relocation of a river, is a key process in the evolution of subaerial fans, river floodplains and deltas. The causes of avulsion are poorly understood, which is partly due to the scarcity of field studies of present avulsions. At present, two avulsions are occurring on the middle and lower Taquari megafan, Pantanal basin, south‐western Brazil. Here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes. The middle fan avulsion (started in 1997–1998) is a result of upstream control: overbank aggradation was caused by the (variable) input of sandy sediment into the system, which caused channel‐belt superelevation and also created an easily erodible subsurface favouring bank retreat, crevassing, and scour of deep floodplain channels. The sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage. The lower fan avulsion (started c. 1990) results from interplay of upstream and downstream controls, the latter being related to the local base level (the Paraguay River floodplain) at the toe of the fan. Channel and overbank aggradation on the lower fan was influenced by fan sub‐lobe progradation and channel backfilling. Fan sub‐lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel. Avulsions are commonly supposed to be preferentially triggered by high‐magnitude floods, when there is considerable channel‐belt superelevation. However, both avulsions studied by us were triggered by small to average floods, with modest channel‐belt superelevation. We conclude that flood magnitude and channel‐belt superelevation have been overrated as causes of avulsion, and demonstrate additional causes that influence the growth of crevasses into avulsions. Copyright © 2012 John Wiley & Sons, Ltd.

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“…The GPR technology is quite versatile and has been consolidated since the 1980s. Currently, geoscientists have applied the GPR method in a range of approaches, such as interference mapping [12][13][14][15][16][17][18][19][20][21][22][23], natural resources exploration [24][25][26][27], environmental contamination studies [28][29][30][31], archaeological studies [32][33][34][35][36][37][38], forensic studies [39][40][41], sedimentological studies [42][43][44][45], studies of rivers and lakes [46][47][48], and so forth.…”

Section: Gpr Methodsmentioning

confidence: 99%

GPR Survey on an Iron Mining Area after the Collapse of the Tailings Dam I at the Córrego do Feijão Mine in Brumadinho-MG, Brazil

2019

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This article shows the interesting results of a pioneer effort by IAG/USP researchers to use ground-penetrating radar (GPR) for humanitarian purposes, guiding the rescue of victims in the tragedy of Brumadinho. The tailings Dam I at the Córrego do Feijão iron ore mine, located in the Brumadinho complex, Minas Gerais State, Brazil, collapsed on 25 January 2019. About 11.7 million m3 of mining mud was spilled from the dam, burying bodies, equipment, structural buildings, buses, and cars along a length of 8.5 km up to the Paraopeba River. Additionally, the contaminated mud traveled more than 300 km along the bed of the Paraopeba River toward the São Francisco River. This work shows the results of a geophysical investigation using the GPR method 17 days after the event. To carry out the geophysical survey, an excavator was used for soil compaction. The data acquisition was performed on the tracks left by the excavator chain using SIR-4000 equipment and antennas of 200 and 270 MHz (GSSI). The GPR studies aimed to map bodies, structural buildings, and equipment buried in the mud. The location of the profiles followed preferably the edge of the slope due to the higher probability of finding buried bodies and objects. The GPR results allowed the detection of subsoil structures, such as concentrations of iron ore and accumulations of sand from the dam filter. The GPR was effective because the iron ore sludge in the mixing process became porous and the pores were filled with air, which provided penetration and reflection of the GPR electromagnetic waves up to a depth of 3.5 m. The results were surprising. Although no bodies or underground equipment were found, the results of this research served to eliminate the studied areas from future excavations, thus redirecting the rescue teams and optimizing the search process. These important results can serve as an additional motivation for the use of GPR in future humanitarian work in areas of tragedies.

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Application of GPR in the Study of a Modern Alluvial Megafan: The Case of the Taquari River in Pantanal Wetland, West-Central Brazil

Cited by 13 publications

References 9 publications

Holocene stratigraphic evolution of saline lakes in Nhecolândia, southern Pantanal wetlands (Brazil)

Holocene stratigraphic evolution of saline lakes in Nhecolândia, southern Pantanal wetlands (Brazil)

Upstream and downstream controls of recent avulsions on the Taquari megafan, Pantanal, south‐western Brazil

GPR Survey on an Iron Mining Area after the Collapse of the Tailings Dam I at the Córrego do Feijão Mine in Brumadinho-MG, Brazil

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