Man's action and slope erosion. A case study in Tâmega basin (1981)

Abstract

When a catastrophic landslide occurred in a small river basin on the left bank of the Tamega valley, in the Northeast of Portugal, which involved the sudden sliding of several tons of arable land and rocks and caused the destruction of a house and the death of fifteen people, the authors decided to carry out a careful investigation of this geomorphological phenomenon. After having formulated a number of hypotheses, they did a lot of field workin the area and carried out measurements to determine, as accurately as possible, both the real extension and the causes of the occurrence of such a phenomenon in that particular place and at that particular time of the year. A series of studies enabled the authors to come the conclusion that the natural and human-induced causes had been responsible for the disaster. Disasters like this don't unfortunately constitute isolated incidents. Therefore, the authors think it is very important to study the local geomorphology carefully before any houses or the setting up of any human activity within the territory it is responsible for.

Quaternary evolution of the Marão Mountain and its consequences in the present dynamics

“…Consequently, these two mountain ranges function as a horst both in relation to the group of tectonic depressions where the river Corgo flows and also to the graben of the river Tâmega. In fact, the effects of the orogeny are still to be felt and the neo-tectonics goes on acting on the present relief forms (PEDROSA, A., 1993(PEDROSA, A., , 1994. That is, tectonic action continues to transform them; thus it is a permanent risk that must be taken into account, notably when building infrastructures such as roads, railways, dams and even houses.…”

“…In several recent studies different authors (REBELO, 2001;PEDROSA, 1993PEDROSA, , 1994aPEDROSA, , 1994bPEDROSA, LOURENÇO, FELGUEIRAS, 2001;PEDROSA, MARTINS, 2001;PEDROSA, BATEIRA, SOARES,1995;PEDROSA, MARQUES, 1994) have tried to systematise the factors that are of greater importance for the onset of these processes in northern Portugal. Natural factors that can influence the occurrence of debris flows and mass movements have been considered up to this moment.…”

Movimentos em massa no norte de Portugal. Factores da sua ocorrência

“…-O fluxo de detritos de Cavez, verificou-se no dia 27 de Dezembro de 1981 (C. BATEIRA e L. SOARES, 1992; A. PEDROSA e B.S. MARQUES, 1994 ). Consultando os valores de precipitação relativos a este mês, verificamos que foi atingido um total de 527 ,5mm, valor pouco habitual nesta área, que equivale a um tempo de retorno de 15 anos e uma probabilidade de ocorrência, segundo análise da distribuição lognormal, de 6%.…”