A geological contribution to the research on mining subsidence at the Germunde coall mine (NW of Portugal)

[Resumo] Apresenta-se neste trabalho um estudo geológico de pormenor relativo asubsidencia mineira provocada pela explora~ao de carvao na Mina de Germunde (Bacia Carbonífera do Douro, NW de Portugal). Os autores analisam e discutem os diferentes aspectos litológicos e estruturais que condicionam a localizaao das descontinuidades induzidas pela subsidencia, que afloram asuperficie do terreno.[Abstract] The aim of this paper is to present a detailed geological research of the mining subsidence induced by exploitation of the Germunde Coal Mine (Douro Coalfield, NW of Portugal). The authors analyse and discuss the different lithological and structural aspects that control the location of mining subsidence discontinuities appearing at ground surface

Metodologias para a análise de lineamentos geo-estruturais a partir de imagens LANDSAT e SPOT: o exemplo da região entre Vigo e Viana do Castelo (NW da Península Ibérica)

O presente estudo tem como objectivo a apresentação de metodologias para a detecção remota de lineamentos geo-estruturaisa partir de imagens dos satélites LANDSAT e SPOT. Será dada ênfase aos lineamentos com potencial interessegeomorfológico no NW de Portugal Continental e no SW da Galiza (Espanha), através da utilização combinada de dadosespectrais de detecção remota espacial, dos sensores ETM+ e HRVIR (satélites Landsat 7 e SPOT 4, respectivamente), bemcomo de dados altimétricos. A interpretação visual dos dados espectrais foi aperfeiçoada através da aplicação de técnicas deprocessamento digital, que consistiram na melhoria do contraste tonal por expansão linear do histograma e na aplicação deum filtro espacial de realce de contornos não direccional. Foram utilizadas várias composições coloridas RGB para aidentificação de lineamentos estruturais e compararam-se as potencialidades e fragilidades exibidas pela interpretaçãomorfoestrutural que as imagens de satélite permitiram evidenciar para a área de estudo. A identificação deste tipo deestruturas culminou na elaboração de uma cartografia de lineamentos geo-estruturais, que integrou os elementos linearesvectorizados sobre as imagens de satélite e sobre o modelo digitalde terreno (MDT)

Geologia estrutural e geotecnia do maciço granítico do Alto da Cabeça Santa (NW de Portugal): implicações para a gestão do georrecurso da pedreira da Mimosa

This work presents the results of the structural geology, geomorphology and geotechnics studies of block delimitation of a granitic rock mass. For this characterisation, the scanline sampling technique of discontinuities has been applied to the study of free rock mass faces from Mimosa granitic quarry (Alto da Cabeça Santa, Penafiel; NW Portugal). For that purpose, the surrounding area of the open quarry as well as selected granitic outcrops were studied using the following tools: surface geological/geomorphological mapping, structural geology and geotechnics/geomechanics techniques. So, a morphotectonic analysis of topographic map and geological survey has then been carried out. In addition, the evaluation methods of field data for discontinuities sets and the statistical characterisation of their orientation, spacing and extension are also presented. The results achieved at different scales are compared in order to detect the presence of a multiscale fracture network pattern. The use of these techniques for understanding the rock mass block delimitation may contribute to improve the sustainable management of the georesources from Mimosa granitic quarry

Insignificant impact of prescribed fire on surface soil in a Pinus pinaster plantation, northern Portugal

Following a prescribed fire in a Pinus pinaster forest site located in the north-west Portugal, monitoring of any changes in selected soil characteristics and soil hydrology was undertaken to assess the effects of burning on the following: pH, electrical conductivity, water content, organic carbon and porosity. Thirty plots were established on a regular grid. At each sample plot before and after the fire, samples were collected (disturbed samples from depths of 0-1cm and 1-5cm; undisturbed core samples from 0-5cm). The results indicate that there was no measurable impact on the properties of the soil following this carefully conducted prescribed fire. The fire only affected the litter layer, as intended. Confirmation of this minimal impact on the soil was provided by regrowth of grasses and herbs already occurring two months after the fire. The implication is, therefore, that provided this wildfire-risk reduction strategy is carried out under existing strict guidelines, any impact on soil quality will be minimal