Dyke-impounded fresh groundwater resources in coastal and island volcanic aquifers: Learning from the El Hierro Island (Spain)

  1. Miguel Ángel Marazuela
  2. Carlos Baquedano Estévez
  3. Noelia Cruz Pérez 1
  4. Jorge Martínez-León
  5. Chrysi laspidou
  6. Jon Jiménez Beltrán
  7. Juan Carlos Santamarta 1
  8. Alejandro García Gil
  1. 1 Universidad de La Laguna
    info

    Universidad de La Laguna

    San Cristobal de La Laguna, España

    ROR https://ror.org/01r9z8p25

Actas:
XI Congreso Geológico de España

Editorial: Sociedad Geológica de España

ISSN: 1576-5172,  2792-2308

Año de publicación: 2024

Páginas: 640

Tipo: Aportación congreso

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Resumen

Freshwater in coastal and island aquifers is a valuable resource whose availability is stronglyconditioned by geological heterogeneity. More than 80 % of the Earth’s surface is of volcanic origin, butthe effect of volcanic dykes on the geometry of the saline interface that separates freshwater fromseawater is still underexplored. This study analyses the impact of volcanic dykes on the depth of thesaline interface in coastal and island aquifers and, subsequently, on the availability of fresh groundwater.Hydrogeological and hydrochemical data from a gallery, perpendicularly crossing several tens of dykes,were integrated with 2D numerical modelling on the volcanic island of El Hierro (Canary Islands, Spain).Measured hydraulic heads demonstrated that the presence of dykes increased the hydraulic gradient bymore than an order of magnitude, with respect to an adjacent area not affected by dykes. Numericalassessment confirmed that the lower the hydraulic conductivity of the dykes, the greater the depth of thesaline interface inland. This impact led to fresh groundwater reserves increasing inland, relative to ahypothetical case without dykes. Numerical simulations also demonstrated that dykes can preventsalinization of production wells in coastal and island aquifers. Locating production wells far enoughinland in an area affected by dykes allowed a higher freshwater extraction rate than if dykes did not exist.Near the coastline, the effect tended to be the opposite. These results will be key to improving themanagement of fresh groundwater resources in coastal volcanic aquifers, and especially on volcanicislands such as the Hawaiian Islands or the Macaronesian archipelagos.