Chapter 8 Eruptive history of Fogo Volcano, São Miguel, Azores

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Sete Cidades is an active central volcano on the western part of São Miguel. The geological record reveals that subaerial activity started more than 250 ka ago. Stratigraphic units defined for Sete Cidades deposits reflect major events in the history of the volcano and are organized into two main groups: the Inferior Group and the Superior Group. Caldera formation resulted from three major paroxysmal events that occurred at about 36, 29 and 16 ka ago. Analysis of the eruptive history of Sete Cidades shows that effusive or moderately explosive eruptions, of Hawaiian and/or Strombolian styles, were located on the slopes of the central volcano. Conversely, trachytic explosive activity is mostly centred inside the caldera involving, in a first stage, predominantly Plinian and sub-Plinian phenomena, changing about 5 ka ago to a dominant hydromagmatic style. Trachytic effusive eruptions are represented by domes and associated lava flows that crop out in the inner caldera walls and on the western slopes of the volcano. Offshore submarine activity is represented by the historic Surtseyan eruptions of 1638 and 1811. In the last 5 ka Sete Cidades was the most active central volcano in the Azores with 17 explosive eruptions predominantly with hydromagmatic character. Scoria conesThese are the most common volcanic edifices on Sete Cidades massif and were formed as a result of the accumulation of basaltic † Deceased 19 May 2012.

Section: Sete Cidades Volcano Eruptive Historymentioning

confidence: 99%

Section: Construction Of the Central Volcanomentioning

confidence: 99%

Section: The Post-caldera Volcanismmentioning

confidence: 99%

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Chapter 7 Eruptive history and evolution of Sete Cidades Volcano, São Miguel Island, Azores

Queiroz

Gaspar

Guest

et al. 2015

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“…Fogo Volcano (Wallenstein 1999;Wallenstein et al 2015) dominates the central part of the island (Fig. 6.2) and its formation began around 200 ka bp (Muecke et al 1974).…”

Section: Fogo Volcanomentioning

confidence: 99%

Chapter 6 Volcano-tectonic structures of São Miguel Island, Azores

Carmo

Madeira

Ferreira

et al. 2015

The Azores archipelago is located at the triple junction between the Eurasia, Nubia and North America lithospheric plates. São Miguel Island, situated at the southeastern part of the western segment of the Azores-Gibraltar Fracture Zone, presents an east-west elongated shape, comprising three quiescent central volcanoes with summit calderas linked by zones of fissure volcanism. The eastern part of the island is older and inactive. Active faulting is represented by prominent fault scarps that constitute important extensional structures, or by linear volcanic structures in fissural volcanic zones, with a dominant NW-SE to WNW-ESE trend. Although less frequent, there are also NNW-SSE to north-south, NE-SW and east-west faults, reflected by some volcanic alignments and linear segments of the drainage system and sea cliffs. The geometric and kinematic data are in agreement with that observed in the rest of the archipelago. However, at eastern São Miguel Island data indicate two distinct groups of conjugated faults characterized by three-dimensional strain: NW-SE to WNW-ESE normal dextral structures are conjugated with NNW-SSE normal left-lateral faults and NW-SE to WNW-ESE normal left-lateral faults are conjugated with NE-SW normal dextral structures, showing the presence of two different stress fields separated in time.

“…Fogo Volcano is located in the central part of the island and its formation began about 200 ka ago (Muecke et al 1974;Wallenstein et al 2015). Five trachytic explosive eruptions took place in the area during the last 5 ka.…”

Section: Fogo and Furnas Volcanoes Geological Settingmentioning

confidence: 99%

Chapter 20 Permanent monitoring of soil CO ₂ degassing at Furnas and Fogo volcanoes (São Miguel Island, Azores)

Viveiros

Ferreira

Silva

et al. 2015

Eight years of permanent soil CO 2 diffuse degassing monitoring at Furnas and Fogo volcanoes shows that several environmental variables may influence soil CO 2 flux to a different extent depending on the location. Stepwise multivariate regression analysis applied to the data acquired by the permanent flux stations installed on São Miguel showed that the monitored environmental variables may influence the gas flux in a proportion between 18 and 51%. The external variables that most significantly correlate with the soil CO 2 flux values for Fogo and Furnas volcanoes monitoring sites are the rainfall/soil water content with its effect on permeability; the barometric pressure pumping effect; the wind speed owing to the atmospheric air intrusion and the air temperature through the action of atmospheric tides. These variables are responsible not only for spike-like oscillations in CO 2 emission, but also for the long-term oscillations with higher and lower values registered usually during winter and summer months, respectively. Residual time-series, calculated using regression models, are compared with other geophysical and geochemical monitoring data in order to recognize changes that may be correlated with the volcanic/hydrothermal systems.