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Contribuição para o estudo da estratigrafia dos vulcões Fogo e Furnas (S. Miguel, Açores) : implicações para a sua história eruptiva recente
| Name: | Description: | Size: | Format: | |
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| Resumo, Índice, Introdução | 1.7 MB | Adobe PDF | ||
| Documento Principal | 29.39 MB | Adobe PDF |
Authors
Abstract(s)
Os vulcões Fogo e Furnas correspondem a dois dos três vulcões centrais ativos de São Miguel e ocupam a parte central e Este da ilha, respetivamente. Ao longo das suas histórias eruptivas produziram um vasto leque de produtos vulcânicos.
A história eruptiva recente (<5.000 anos) do Vulcão do Fogo foi marcada por erupções explosivas de estilo Subpliniano, frequentemente com carácter hidromagmático. No entanto, foi o único vulcão que produziu uma erupção Pliniana neste período de tempo, que originou o depósito Fogo A.
No Vulcão das Furnas ocorreram 10 erupções explosivas nos últimos 5.000 anos associadas a magmas traquíticos, por vezes com extrusão de domos.
Durante estre trabalho foi possível caracterizar o depósito da erupção explosiva de 1563 do Vulcão do Fogo e o depósito Furnas E, produzido pelo Vulcão das Furnas. A erupção de 1563 foi a última erupção de estilo Subpliniano que ocorreu no interior da caldeira do Vulcão do Fogo e foi seguida (4 dias depois) por uma erupção Havaiana no topo de um domo traquítico. A erupção de estilo Subpliniano teve um volume de 0,421 Km3 e a coluna eruptiva atingiu cerca de 19 km de altura.
O depósito da erupção do Fogo de 1563 foi dividido em dois membros principais, o Membro Inferior e o Membro Superior. O Membro Inferior é, maioritariamente, composto por níveis de cinza fina e apresenta um único nível de lapilli pomíticos. O Membro Superior é, predominantemente, composto por níveis de lapilli pomíticos, intercalados por leitos de cinza fina, e por níveis de cinza fina onde ocorrem estratificações de lapilli finos.
Estas frequentes alternâncias sugerem importantes mudanças no tipo de atividade e fragmentação durante a erupção, o que conferiu instabilidade à coluna eruptiva.
O depósito Furnas E resultou de uma erupção de estilo Subpliniano que ocorreu no interior do complexo de caldeiras do Vulcão das Furnas.
Durante o presente trabalho foi possível datar, pela primeira vez, o depósito Furnas E e atribuir-lhe uma idade de 1520±30 anos B.P. A erupção teve um volume total de 0,24 Km3 (Booth et al., 1978) e coluna eruptiva estimada de 19-20 km, através dos dados de Booth et al. (1978). O depósito é, maioritariamente, constituído por níveis de cinza fina e apresenta um único nível de lapilli pomíticos bem calibrados.
As características destes dois depósitos permitem evidenciar importantes alternâncias no estilo de atividade durante as erupções, à semelhança do que acontece com as restantes erupções dos vulcões centrais da ilha, o que sugere que os processos eruptivos são recorrentes nestes vulcões, associados a importantes sistemas hidrológicos.
O trabalho realizado permitiu a determinação dos parâmetros eruptivos da erupção do Fogo de 1563. Com base nos dados obtidos efetuaram-se simulações da dispersão e deposição de tefra para o depósito total e para um leito individual (L2), que representa o maior pulso da erupção. Apesar das simulações efetuadas com base nos parâmetros da unidade L2 serem mais realistas, dado que se trata de um leito bem caracterizado, é através das simulações realizadas para a totalidade do depósito que se consegue obter a área máxima suscetível de ser afetada por uma erupção semelhante à de 1563 do Vulcão do Fogo. Os dois casos são semelhantes, evidenciando a dispersão tendencial dos depósitos para a parte Este da ilha.
Os mapas obtidos no decurso deste trabalho constituem uma abordagem à avaliação dos perigos vulcânicos, contribuindo para uma melhor preparação de respostas a catástrofes.
ABSTRACT: Fogo and Furnas are two of the three active central volcanoes of São Miguel that occupy the central and the eastern part of the island, respectively. Throughout their eruptive histories they produced a wide range of volcanic products. The recent eruptive history (last 5 ka) of Fogo volcano was dominated by explosive eruptions of Subplinian style, frequently with hidromagmatic character. However, it was the only volcano that produced a Plinian eruption in this period of time, which originated the Fogo A deposit. In Furnas Volcano occurred 10 explosive eruptions during the last 5.000 years associated to trachytic magmas, sometimes with the extrusion of domes. During this work it was possible to physically characterize the deposit produced during Fogo 1563 eruption and also the deposit Furnas E, produced by Furnas volcano. The eruption of 1563 was the last of Subplinian style that occurred inside of Fogo volcano caldera and was followed (4 days later) by a Hawaiian eruption at the top of a trachytic dome. The Subplinian eruption had a volume of 0.421 Km3 and the eruptive column reached 19 km in height. Fogo 1563 deposit was divided into two main members, the Lower and Upper members. The Lower Member is mostly composed of ash layers and includes only one pumice lapilli bed. The Upper Member is mostly comprised of pumice layers with fine ash beds and by ash levels with fine-grained pumice lapilli stratifications. The frequent alternations between ash and pumice levels suggest important changes of the type of activity and fragmentation during the eruption, which gave some instability to the eruptive column. Furnas E deposit resulted from an eruption of Subplinian style that occurred inside of Furnas volcano calderas complex. During this work it was possible to estimate the age of 1520±30 years B.P for Furnas E deposit. The eruption had a total volume of 0.24 km3 (Booth et al., 1978) and an estimated eruptive column of 19-20 km, using data from Booth et al. (1978). The deposit is mostly composed of fine-grained ash levels and has only one well sorted fine-grained pumice layer. The characteristics of the Fogo 1563 and Furnas E deposits show important alternations in the style of activity during the eruptions, similar to what happens with the other eruptions from the three active central volcanoes of the island, suggesting that the eruptive processes are recurrent in these volcanoes, associated with important hydrological systems. It was possible to determinate the eruptive parameters for the 1563 eruption from Fogo volcano. Based on the results some simulations were performed for the total deposit and for L2 layer, which corresponds to the largest pulse of the entire eruption. Although the simulations made with eruptive parameters calculated for unit L2 are more realistic, once it is a well characterized bed, it is through the simulations for the total deposit that we can have the maximum area susceptible of being affected, during an event similar to the 1563 eruption from Fogo volcano. Both cases are similar, showing a trend dispersion of the deposits to the eastern part of the island. The resulting maps constitute an approach to the evaluation of volcanic hazards, contributing for a better preparation of responses to catastrophes.
ABSTRACT: Fogo and Furnas are two of the three active central volcanoes of São Miguel that occupy the central and the eastern part of the island, respectively. Throughout their eruptive histories they produced a wide range of volcanic products. The recent eruptive history (last 5 ka) of Fogo volcano was dominated by explosive eruptions of Subplinian style, frequently with hidromagmatic character. However, it was the only volcano that produced a Plinian eruption in this period of time, which originated the Fogo A deposit. In Furnas Volcano occurred 10 explosive eruptions during the last 5.000 years associated to trachytic magmas, sometimes with the extrusion of domes. During this work it was possible to physically characterize the deposit produced during Fogo 1563 eruption and also the deposit Furnas E, produced by Furnas volcano. The eruption of 1563 was the last of Subplinian style that occurred inside of Fogo volcano caldera and was followed (4 days later) by a Hawaiian eruption at the top of a trachytic dome. The Subplinian eruption had a volume of 0.421 Km3 and the eruptive column reached 19 km in height. Fogo 1563 deposit was divided into two main members, the Lower and Upper members. The Lower Member is mostly composed of ash layers and includes only one pumice lapilli bed. The Upper Member is mostly comprised of pumice layers with fine ash beds and by ash levels with fine-grained pumice lapilli stratifications. The frequent alternations between ash and pumice levels suggest important changes of the type of activity and fragmentation during the eruption, which gave some instability to the eruptive column. Furnas E deposit resulted from an eruption of Subplinian style that occurred inside of Furnas volcano calderas complex. During this work it was possible to estimate the age of 1520±30 years B.P for Furnas E deposit. The eruption had a total volume of 0.24 km3 (Booth et al., 1978) and an estimated eruptive column of 19-20 km, using data from Booth et al. (1978). The deposit is mostly composed of fine-grained ash levels and has only one well sorted fine-grained pumice layer. The characteristics of the Fogo 1563 and Furnas E deposits show important alternations in the style of activity during the eruptions, similar to what happens with the other eruptions from the three active central volcanoes of the island, suggesting that the eruptive processes are recurrent in these volcanoes, associated with important hydrological systems. It was possible to determinate the eruptive parameters for the 1563 eruption from Fogo volcano. Based on the results some simulations were performed for the total deposit and for L2 layer, which corresponds to the largest pulse of the entire eruption. Although the simulations made with eruptive parameters calculated for unit L2 are more realistic, once it is a well characterized bed, it is through the simulations for the total deposit that we can have the maximum area susceptible of being affected, during an event similar to the 1563 eruption from Fogo volcano. Both cases are similar, showing a trend dispersion of the deposits to the eastern part of the island. The resulting maps constitute an approach to the evaluation of volcanic hazards, contributing for a better preparation of responses to catastrophes.
Description
Dissertação de Mestrado, Vulcanologia e Riscos Geológicos, 14 de fevereiro de 2019, Universidade dos Açores.
Keywords
Erupções Vulcânicas Sismicidade Histórica Vulcão das Furnas Vulcão do Fogo Vulcanismo Ilha de São Miguel (Açores) Fogo Volcano Furnas Volcano Azores
Citation
Aguiar, Simone Correia. "Contribuição para o estudo da estratigrafia dos vulcões Fogo e Furnas (S. Miguel, Açores): implicações para a sua história eruptiva recente". 2019. 202 p.. (Dissertação de Mestrado em Vulcanologia e Riscos Geológicos). Ponta Delgada: Universidade dos Açores, 2018. [Consult. Dia Mês Ano]. Disponível em www:<http://hdl.handle.net/10400.3/5079>.