DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
Navegar
3 resultados
Resultados da Pesquisa
Item Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil.(2005) Bacellar, Luis de Almeida Prado; Coelho Netto, Ana Luiza; Lacerda, Willy AlvarengaHundreds of gullies (‘voçorocas’) of huge dimensions (up to 400–500 m long, 150 m wide and 50 m deep) are very common in the small Maracujá Catchment in southeastern Brazil. These erosional features, which occur with an uneven intensity throughout the area, started due to bad soil management practices at the beginning of European settlement, at the end of the 17th century, and nowadays are still evolving, but at a slower rate. As surface soils are usually very resistant to erosion, the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning. An analysis of well known erosion controlling factors was performed, aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution. Data shows that geology and, mainly, geomorphology are the main controlling factors, since gullies tend to be concentrated in basement rock areas with lower relief (domain 2) of Maracujá Catchment, mainly at the fringes of broad and flat interfluves. At the detailed scale (1:10 000), gullies are more common in amphitheatre-like headwater hollows that frequently represent upper Quaternary gullies (paleogullies), which demonstrate the recurrence of channel erosion. So, gullies occur in areas of thicker saprolites (domain 2), in places with a natural concentration of surface and underground water (hollows). Saprolites of the preserved, non-eroded hollows are usually pressurized (confined aquifer) due to a thick seal of Quaternary clay layer, in a similar configuration to the ones found in hollows of mass movement (mudflow) sites in southeastern Brazil. Therefore, the erosion of the resistant soils by human activities, such as road cuts and trenches (‘valos’), or their mobilization by mudflow movements, seem to be likely mechanisms of gullying initiation. Afterwards, gullies evolve by a combination of surface and underground processes, such as wash and tunnel erosion and falls and slumps of gully walls.Item Análise da erodibilidade de saprolitos de gnaisse.(2004) Morais, Fernando de; Bacellar, Luis de Almeida Prado; Sobreira, Frederico GarciaAs voçorocas são freqüentes em áreas com rochas do embasamento cristalino. A evolução destas feições é sempre fortemente condicionada pelos processos de erosão hídrica subsuperficial, embora os processos superficiais também sejam importantes. Este trabalho objetivou investigar os processos erosivos subsuperficiais atuantes nas voçorocas e compreender que fatores mineralógicos e texturais poderiam influenciar a erodibilidade dos saprolitos. Para tanto, foram realizados ensaios de caracterização e de avaliação da erodibilidade em amostras representativas, sendo o principal destes o ensaio de furo de agulha. Os resultados indicam que a erosão por carreamento não ocorre e que os saprolitos apresentam susceptibilidade variável à erosão por piping, mesmo quando derivados de uma mesma unidade litológica, mas superior à do horizonte B latossólico. Dados preliminares indicam que os saprolitos mais susceptíveis à erosão por piping são os de textura siltosa (determinados em ensaios granulométricos sem defloculante e agitação) e pobres em minerais agregadores, como os argilominerais.Item Avaliação de áreas de risco geológico na bacia de Vargem das Flores, municípios de Betim e Contagem - MG.(2003) Danderfer Filho, André; Paulo, Jacks Richard de; Bacellar, Luis de Almeida PradoThis study was carried out in the Vargem das Flores basin, which is located in Betim and Contagem, Minas Gerais State. The principal aim of this research was to study soil erosion by gullies, which occurred with heterogeneous concentrations throughout this basin. Field data and the remote sensing products allowed the characterization and mapping: of geology, geomorphology, gully features and landuses evolution in the last decades. This methodology have been allowing the evaluation of the geological risk.