Descrição
The morpho-structural evolution of oceanic islands results from competition between volcano growth and
partial destruction by mass-wasting processes. We present here a multi-disciplinary study of the successive
stages of development of Faial (Azores) during the last 1 Myr. Using high-resolution digital elevation model
(DEM), and new K/Ar, tectonic, and magnetic data, we reconstruct the rapidly evolving topography at successive
stages, in response to complex interactions between volcanic construction and mass wasting, including
the development of a graben. We show that: (1) sub-aerial evolution of the island first involved the rapid
growth of a large elongated volcano at ca. 0.85 Ma, followed by its partial destruction over half a million
years; (2) beginning about 360 ka a new small edifice grew on the NE of the island, and was subsequently
cut by normal faults responsible for initiation of the graben; (3) after an apparent pause of ca. 250 kyr, the
large Central Volcano (CV) developed on the western side of the island at ca 120 ka, accumulating a thick
pile of lava flows in less than 20 kyr, which were partly channelized within the graben; (4) the period between
120 ka and 40 ka is marked by widespread deformation at the island scale, including westward propagation
of faulting and associated erosion of the graben walls, which produced sedimentary deposits;
subsequent growth of the CV at 40 ka was then constrained within the graben, with lava flowing onto the
sediments up to the eastern shore; (5) the island evolution during the Holocene involves basaltic volcanic activity
along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano–
tectonic depression. We conclude that the whole evolution of Faial Island has been characterized by
successive short volcanic pulses probably controlled by brief episodes of regional deformation. Each pulse
has been separated by considerable periods of volcanic inactivity during which the Faial graben gradually developed.
We propose that the volume loss associated with sudden magma extraction from a shallow reservoir
in different episodes triggered incremental downward graben movement, as observed historically, when immediate
vertical collapse of up to 2 m was observed along the western segments of the graben at the end of
the Capelinhos eruptive crises (1957–58).
; Marques, Fernando 
