Changing hazard awareness over two decades: the case of Furnas, São Miguel (Azores)

Furnas (ca. 1,500 inhabitants) lies within the caldera of Furnas volcano on the island of São Miguel (Azores) and has the potential to expose its inhabitants to multiple hazards (e.g. landslides, earthquakes, volcanic eruptions and degassing). The present population has never experienced a volcanic eruption or a major earthquake, although the catalogue records six eruptions, sub-Plinian in style over the last 2 ka years. Today, the area experiences strong fumarolic activity. In the case of an eruption, early evacuation would be necessary to prevent inhabitants being trapped within the caldera. Awareness of potential threats and knowledge of what to do in the case of an emergency would assist in evacuation. In this paper inhabitants' awareness of volcanic and seismic threats in 2017 is compared with those revealed in a similar study completed more than two decades ago. It is concluded that, whereas awareness of earthquakes and the dangers posed by volcanic gas discharge has increased, knowledge of the threat of volcanic eruptions and the need to prepare for possible evacuation has not. Research suggests that changing awareness is related to effective collaboration that has developed between the regional government, through its civil protection authorities and scientists, and the people of Furnas.

Mineralogy and Geochemistry (HFSE and REE) of the Present-Day Acid-Sulfate Types Alteration from the Active Hydrothermal System of Furnas Volcano, São Miguel Island, The Azores Archipelago

Acid-sulfate alteration is comprised by clays, sulfate, sinter and native sulphur minerals crystallized as neoformation products from dissolution of primary minerals during water-rock interaction. Smectite, kaolinite, halloysite-7 Å and opal-A occur in assemblages with alunite. Smectite represents a mechanical mixture between two (propylitic and acid-sulfate) alteration types. High amounts of high-field strength elements (HFSE) and rare earth elements (REE) were measured in acid-sulfate rocks. The Nb vs. Ta and Zr vs. Hf show a positive trend and a widely scattered relationships, suggesting a large fractionation during acid-sulfate alteration. Higher ∑REE amounts (up to 934.5 ppm) were found in clay-sulfate assemblages and lower ∑REE amounts in sinter (opal-A ± sulfate, 169.05 ppm) than to fresh rocks (up to 751.2 ppm). The acid-sulfate rocks reveal a distinctive gull-wing chondrite-normalized pattern with a negative Eu anomaly and light- and heavy-REE “wings” similar to the gull-wing pattern of fresh rocks. The Eu/Eu* shows a large fractionation of acid sulfate rocks from 0.16 to 0.78 with respect to fresh trachyte products (0.10 to 0.38). Variation of (La/Sm)N and (La/Yb)N ratio show a large fractionation of light-REE and heavy-REE. The Y vs. Dy and Y vs. Ho show a very good positive correlation coefficient and a large Y fractionation in acid-sulfate rocks with respect to fresh rocks.