Docteur de l'Université de Lisbonne (Portugal) et de l'université de Paris Sud
Bât. 504, 1er étage
Email: acgcosta@fc.ul.pt - acgcosta.geo@gmail.com
Supervisors:
Collaborations:
- Régis Mourgues (Université Du Maine, Le Mans, France)
- Vicente Soler (Instituto de Productos Naturales y Agrobiología, Tenerife, Canary Islands, Spain)
PhD project: Mass-wasting episodes in the geological evolution of the Azores islands: timing, recurrence, mechanisms and consequences. (Episodes de destruction gravitaire durant l'évolution géologique des îles Açores : âge, récurrence, mécanismes et conséquences).
PhD scholarship funded by FCT (Fundaçao para a Ciência e Tecnologia, Portugal, SFRH/BD/68983/2010). PhD student integrated in the MEGAHazards project, funded by FCT (PTDC/CTE-GIX/108149/2008).
Site web du programme MEGAHazards
Research (Under development):
1 - Occurrence of large-scale destruction in the evolution of volcanic islands: interplay with volcanic growth and the role of an active tectonic setting (Pico-Faial volcanic ridge, Azores)
Azores islands are located near the Triple Junction between Eurasia, Nubia and North-America plates (Fig. 1).
Most of the Azores islands are on a zone that accommodates, in a diffuse manner, the deformation between Nubia and Eurasia plates (Marques et al., 2013), and there has been recorded high magnitude seismicity (e.g., Borges et al., 2007). These islands are either along Terceira Rift (TR), or along steep volcanic ridges parallel to the plate boundary. Though factors like the active tectonic setting and steep slopes are favorable to the destabilization of the volcanic edifices, the published studies addressing Azores islands' evolution do not conclude unequivocally on the occurrence of large-scale mass-wasting events.
This PhD work integrates several approaches (geomorphological analyses, fieldwork, geochronology) in order to study the evolution of one of these steep volcanic ridges (Fig. 1, Pico-Faial), focusing specially the events of large-scale destruction.
Figure 1 - Location of Azores archipelago on the triple junction between the North America (NA), Eurasia (EU) and Nubia (NU) plates. Main active structures represented as thick black lines (Middle Atlantic Ridge - MAR, Terceira Rift - TR) and inactive structure as dashed white line (East Azores Fracture Zone - EAFZ). The islands studied in this PhD project are Faial and Pico. Bathymetric data from Lourenço et al. (1998), and the image is available at http://w3.ualg.pt/~jluis/acores_plateau.htm. Globe image from NOAA.
2 - Monitoring of the active large-scale slump structure in the SE of Pico Island, Azores
The southeastern flank of Pico Island is affected by an active large-scale slump (Hildenbrand, et al. 2012b) (Fig. 2). In order to monitor the evolution of this structure, new GPS and microseismic networks, as well as an inclinometer, were installed in 2012 (in collaboration with Vicente Soler).
Figure 2. A. Pico Island DEM (lighting from NW), and location of the active slump that affects Pico's SE flank; B. Interpretation of the slump structures and deformation detected on the slump area. The SAR data was obtained for the period 2006-2009 and the vertical displacement velocities are in mm/yr. GPS horizontal and vertical velocities resulted from 4 campaigns conducted between 1999-2006. Figure extracted from Hildenbrand et al. (2012b).
3 - Fluid overpressure as a factor promoting the large-scale destabilization of volcanic edifices
In order to assess the destabilizing influence of fluid overpressures developed within the volcanic edifices, analogue modeling experiments were initiated in the Université Du Maine (Le Mans, France), in collaboration with Régis Mourgues (Fig. 3).
Figure 3. Analogue modelling experiment in Université du Maine (Le Mans, France).
Methods/approaches currently applied:
- Geomorphological analysis of high-resolution DEMs
- Fieldwork (volcano-stratigraphy, structural analysis, sampling for K-Ar dating)
- Geochronology (K-Ar Unspiked Cassignol-Gillot Technique)
- Analogue Modelling
(In the future)
1 - Causes for large-scale failure in oceanic islands: influence of edifice internal structure and tectonic setting
2 - Consequences of large-scale catastrophic destruction in oceanic islands:
- tsunami generation;
- change of stress conditions within the volcanic edifice (triggering of volcanic activity).
Methods/approaches to develop in the future:
- Numerical modelling
- Analogue modelling
- Geophysics (onshore and offshore)
- Fieldwork (focused on the study of tsunami deposits)
Publications
Marques, F.O., Catalão, J.C., DeMets, C., Costa, A.C.G., Hildenbrand, A., 2013. GPS and tectonic evidence for a diffuse plate boundary at the Azores Triple Junction. Earth and Planetary Science Letters, in press.
Hildenbrand, A., Marques, F.O., Fernandes, J.C.C.C., Catita, C.M.S., Costa, A.C.G., 2013b. Reply to Mitchell et al.'s comment on our article "Large-scale active slump of the SE flank of Pico Island (Azores)". Geology, in press.
Hildenbrand, A., Marques, F.O., Costa, A.C.G., Sibrant, A.L.R., Silva, P.M.F., Henry, B., Miranda, J.M., Madureira, P., 2013a. Reply to the comment by Quartau and Mitchell on "Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: The Faial Island example (Azores)", J. Volcanol. Geotherm. Res. 241-242, 39-48, by Hildenbrand et al. (2012). Journal of Volcanology and Geothermal Research 255, 127-130. (link)
Hildenbrand, A., Marques, F.O., Fernandes, J.C.C.C., Catita, C.M.S., Costa, A.C.G., 2012b. Large-scale active slump of the southeastern flank of Pico Island, Azores. Geology 40 (10), 939-942. (link)
Hildenbrand, A., Marques, F.O., Costa, A.C.G., Sibrant, A.L.R., Silva, P.M.F., Henry, B., Miranda, J.M., Madureira, P., 2012a. Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: the Faial Island example (Azores). Journal of Volcanology and Geothermal Research 241-242, 39-48. (link)
Education
January 2011 - present - PhD student in Geology at University of Lisbon and Univ. Paris-Sud
2006-2010 - Licence in Geology at University of Lisbon, Portugal
Other references cited in the text:
Borges, J. F., Bezzeghoud, M., Buforn, E., Pro, C., Fitas, A., 2007. The 1980, 1997 and 1998 Azores earthquakes and some seismo-tectonic implications. Tectonophysics 435 (1-4), 37 -54. (link)
Lourenço, N., Miranda, J.M., Luis, J.F., Ribeiro, A., Mendes Victor, L.A., Madeira, J., Needham, H.D., 1998. Morpho-tectonic analysis of the Azores Volcanic Plateau from a new bathymetric compilation of the area. Marine Geophysical Researches 20 (3), 141-156. (link)