Assessment of drainable porosity of a holm soil from soil-water tension

An alternative way to assess the drainable porosity as a function of soil-water tension, from the soil-water retention curve (Van Genuchten's model), is presented for data of a clayey holm gley soil of the county of Piracicaba, SP, Brazil. Soil-water retention curves were determined using undisturbed soil samples. The analysis of the results has shown that the data variability was mainly due to random causes. Statistical indexes used to verify the degree of fitting of the experimental data to the proposed model, have shown that the model can be used to estimate the drainable porosity from the empirical parameters of the Van Genuchten model.Um modo alternativo para estimativa da porosidade drenável em função da tensão da água no solo a partir da equação de VAN GENUCHTEN para a curva de retenção, é apresentado e testado para dados obtidos de um solo de várzea ( Gleissolo Eutrófico, textura argilosa). Curvas de retenção de água foram elaboradas com amostras de solo com estrutura indeformada. Na análise dos resultados verificou-se que o maior componente de erro foi devido a causas aleatórias, representando cerca de 12 vezes o erro sistemático. Os índices estatísticos utilizados para verificar o grau de ajuste dos dados experimentais à relação funcional apresentada entre porosidade drenável e tensão de água no solo, mostraram que esta relação pode ser utilizada para estimativa da porosidade drenável, a partir do conhecimento dos parâmetros empíricos da equação de VAN GENUCHTEN

Comparative behaviour and evolution of the caldera forming active volcanoes of Sao Miguel (Azores): Sete Cidades, Fogo and Furnas

São Miguel, with its E-W elongated shape, is the largest and the most volcanically active of the nine islands of the Azores archipelago. From West to East Sete Cidades, Fogo and Furnas are three active central volcanoes with calderas. Each of these three calderas evolved through several phases of collapse generated by Plinian scale explosive eruptions over the last 40 ka. The most recent Plinian scale eruption was that of Fogo A, c. 5ka, from Fogo volcano. In this report, we summarise the results of more than two decades of research on the geology of these volcanoes. More specifically we compare: the evolution of each caldera; and the styles of recent eruptions. It is of note that there is a pattern of a change in eruptive behaviour from around 5 ka shown by all three volcanoes to eruptions displaying a style involving switching between magmatic and phreatomagmatic sub-Plinian activity. This is well displayed in the historic sub-Plinian eruptions of Fogo and Furnas