Chapter 21 Hydrogeology of São Miguel Island, Azores: a review

Abstract

Groundwater is the main source of water supply on São Miguel. Groundwater abstraction (25 hm 3 a 21 ) relies almost exclusively on springs discharging from perched aquifers. A total of 1100 springs (1.5 springs/km 2 ) are located on São Miguel, mainly in the Á gua de Pau and the Furnas-Povoação groundwater bodies. Only 26 wells have been drilled, distributed principally in the west-central zone. Specific capacity ranges between 0.49 and 100 l (s m) 21 (median ¼ 1.11 l (s m) 21 ), while transmissivity ranges between 5.98 Â 10 24 and 1.22 Â 10 21 m 2 s 21 (median ¼ 1.35 Â 10 23 m 2 s 21 ). Groundwater is predominantly of the Na-Cl and Na-HCO 3 types and electrical conductivity in springs ranges from 36 to 440 mS cm 21 (median ¼ 152 mS cm 21 ), which is lower than in wells (211-9670 mS cm 21 ; median ¼ 515 mS cm 21 ). These values result from seawater spray, a CO 2 soil contribution and limited dissolution of primary silicate minerals from volcanic rocks. In the case of wells, seawater intrusion may also influence electrical conductivity. One of the main problems in groundwater quality is total and faecal coliform microbial contamination. A pollution risk map constructed for São Miguel as a whole showed that risk in the majority of the groundwater bodies is only very low to moderate.

Hydrogeochemistry and Strontium Isotopic Signatures of Mineral Waters from Furnas and Fogo Volcanoes (São Miguel, Azores)

“…Furnas also presents a large number of secondary manifestations of volcanism, such as fumaroles and steaming grounds [19], as well as numerous mineral waters discharges [15,16]. The degassing manifestations at Furnas volcanic system are located both inside the caldera and in the south flank of the volcano, at Ribeira Quente village.…”

“…In volcanic Azores archipelago numerous mineral water discharges are spread along the territory [14][15][16][17], namely in seven of the nine islands (São Miguel, Terceira, São Jorge, Pico, Faial, Graciosa, and Flores), presenting a wide range of dissolved solid content, hydrochemical characteristics, and temperature. Other secondary manifestations of volcanism also occur in the Azores archipelago, such as hydrothermal fumaroles and diffuse degassing areas [18][19][20].…”

Chapter 1 Volcanic geology of São Miguel Island (Azores Archipelago): introduction

“…The final section on Natural resources begins with a review by Coutinho et al (2015) of the hydrogeology of São Miguel, while Rangel et al (2015) present recent data on the use of geothermal resources. It is emphasized that basaltic lava flows, ignimbrites and hydromagmatic tuffs are often used as raw material for building, whereas scoriaceous pyroclastics are used in road construction.…”