Water prospection in volcanic islands by Time Domain Electromagnetic (TDEM) surveying: The case study of the islands of Fogo and Santo Antão in Cape Verde

• Published in: Journal of applied geophysics Vol. 134; pp. 226 - 234
• Main Authors: Martínez-Moreno, F.J., Monteiro-Santos, F.A., Madeira, J., Bernardo, I., Soares, A., Esteves, M., Adão, F.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2016
• Subjects: Cape Verde; Groundwater resources; Time Domain Electromagnetics (TDEM); Trade winds; Volcanic islands; Cape Verde; Groundwater resources; Volcanic islands; Trade winds; Time Domain Electromagnetics (TDEM)
• ISSN: 0926-9851; 1879-1859
• DOI: 10.1016/j.jappgeo.2016.09.020

Water demand in islands, focused in agriculture, domestic use and tourism, is usually supplied by groundwater. Thus the information about groundwater distribution is an important issue in islands water resources management. Time Domain Electromagnetic (TDEM) provides underground resistivity distribution at greater depths and is of easier application than other methods. In this study TDEM technique was used for groundwater prospection in two volcanic islands with water supply problems, the islands of Fogo and Santo Antão in the Republic of Cape Verde. The 10 islands of Cape Verde Archipelago, located off the coast of Senegal (W Africa), present a semi-arid climate and thus suffer from irregular and scarce precipitation. In the Island of Fogo 26 TDEM soundings, presenting an area distribution, were performed on the SW flank of the volcanic edifice. These allowed obtaining a 3D model composed of 5 layers parallel to the topographic surface separated by 50m depth down to −250m. The results indicate the presence of the water-table at a depth of 150m in the lower ranges of the W flank of the island, and at >200m depth in the area above 250m above sea level (a.s.l.). In the Island of Santo Antão 32 TDEM soundings, distributed along 5 linear profiles, were obtained on the north-eastern half of the island. The profiles are located in two regions exposed to different humidity conditions to the N and S of the main water divide. The northern flank receives the dominant trade winds first and most of the precipitation and, therefore, the water-table is shallower (~50m depth) than in the S (~100m depth). Our study demonstrates the applicability and usefulness of the TDEM method for groundwater prospection in high resistivity contexts such as in volcanic islands. •The islands of Fogo and Santo Antão in Cape Verde present water supply problems.•Groundwater prospection by previous geophysical was unsuccessful.•TDEM soundings, distributed in area and in profile, were measured.•In the leeward flank of Fogo the water-table is at −150m in areas below 250m a.s.l.•The windward flank of Santo Antão presents a shallower water table at ~50m depth.