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Unravelling the heterogeneous character of porous lava rocks from Fogo Volcano (Azores, Portugal) through experimental data

Maria Luísa Pereira1, 2, Nora Cueto3, Lucia Pappalardo4, Gianmarco Buono4, Alessia Falasconi4, Mário Moreira5, Vittorio Zanon1, Isabel Fernandes6

  • Affiliations:  1Instituto de Investigação em Vulcanologia e Avaliação de Riscos (IVAR), Universidade dos Açores, Rua Mãe de Deus, Ponta Delgada 9500-123, Portugal; 2Faculdade de Ciências e Tecnologia, Universidade dos Açores, Rua Mãe de Deus, Ponta Delgada 9500-123, Portugal; 3Instituto de Geociencias IGEO (CSIC - UCM), c/Doctor Severo Ochoa, 7, 28040 Madrid, Spain; 4Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Via Diocleziano, 328, 80124 Naples, Italy; 5Instituto Superior de Engenharia de Lisboa, Departamento de Física, R. Conselheiro Emídio Navarro 1, 1959-007 Lisboa, Portugal; 6Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 142

  • Programme No: 3.1.34

  • Theme 3 > Session 1

Abstract

This research focuses on the heterogeneity analysis of intermediate composition lavas from the Fogo Volcano (or Água de Pau Volcano, Azores, Portugal) using the through-transmission method, standardised determination of water absorption by capillarity, and X-ray microtomography. Ultrasonic velocities and capillarity absorption were measured along three orthogonal directions in six cubic specimens to assess how pore structure varies and influences rock physics parameters. Unconfined compressive strength (UCS) was determined in three cores from a single cube. The bimodal pore size distribution leads to an anomalous capillary imbibition, with two absorption processes described as additive by the applied Sharp Front model. Capillary-connected porosity (5.07%) is lower than total connected porosity (18.5--20.1%), as gravitational fluid transport dominates due to large pores (>1 mm). P-wave velocities (2802--3208 m/s) are largely insensitive to pore shape, while Vp/Vs ratios (1.76 ± 0.25), dynamic Young's modulus (16.78 ± 3.20 GPa), and Poisson's ratio (0.23 ± 0.11) reflect vesicular textures independent of vesicle orientation. Simulated core permeability (0.7--6.6 mD) decreases with increased tortuosity despite higher connected porosity in some samples. UCS ranges from 15.5 to 36.0 MPa and depends on pore size, shape, orientation to the loading direction, and connected porosity. Failure occurs by tensile splitting, with fractures initiating at pore edges and plagioclase phenocryst borders. While capillarity and Vp/Vs ratios show limited directional variation, vesicle shape and size affect strength and fluid transport mechanisms. These findings highlight the heterogeneous physical characteristics of lavas, providing insights for interpreting field measurements and enhancing volcano stability models.