Hotspot dominated rifting: Volcanic island evolution and collateral geo-hazards resulting from cascading geodynamic processes - The instance of Sao Miguel (south-eastern Terceira Rift, Azores)
Final Report Abstract
The Terceira Rift is located at the westernmost tip of the Eurasian-Nubian (African) plate boundary where it links a major transform fault (Gloria Fault) with the Mid-Atlantic ridge (MAR) oblique to the regional extension induced by plate kinematics. The rift is defined by a succession of deep basins and bathymetric highs or islands, all of them of volcanic origin. Both, the volcanic origin of the island and its location at the Eurasian-Nubian plate boundary are very present facts for the about 140,000 inhabitants, since seismicity and hydrothermal activity highly influence their workaday life and remind them of the significant risk potential. The Terceira Rift has developed orthogonally to previous SW-NE directed extensional stress, before a clockwise rotation in extension to WSW-ENE led to a rearrangement of the tectonic regime within the inherited setting and the creation of NNW-SSE trending faults and volcanic lineaments (e.g. the Monaco Bank south of São Miguel Island). This highlights the Terceira Rift to be a re-organized rift system predominantly controlled by plate kinematics. Rift tectonics additionally control submarine sedimentation since, on the one hand, fault scarps and volcanic lineaments deflect turbidity and bottom currents. On the other hand, associated seismicity destabilizes high local accumulations of sediments, such as turbidites or drift deposits, and causes retrograde erosion of the shelf break forming downslope channel systems. Hence, mass wasting is a common phenomenon at the southeastern Terceira Rift involving sliding, slumping and flank collapsing. Sediments particularly results from São Miguel’s onshore and coastal erosion. Shelf erosion and remobilization of shelf deposits along the northern coast resulted/result in unconfined turbidity currents forming large sediment lobes at the island slope - most likely due to the exposure to North-Atlantic storm swell. These sediment lobes are incised by channel systems discharging the constant terrestrial and fluvial sediment supply of the island by confined turbidiy currents. In contrast, turbidity currents at the southern slope generate cyclic steps, chutes-and-pools and turbidite lobes. High-resolution bathymetry allowed mapping of 252 submarine volcanic cones, which are - based on a combined morphological and seismic interpretation – associated with explosive eruptions. Since the morphological characteristics do not vary with water depth (ranging from 120 m to 3200 m) and resemble those of monogenetic alkali-basaltic cinder cones onshore São Miguel, their eruption histories are assumed to be 1) independent of the water depth, and 2) comparable to onshore cinder cones. Submarine cones in the southeastern Terceira Rift are either controlled by faults, are secondary parasitic features of the onshore stratovolcanoes or superimpose an independent submarine volcanic system. Since the cones show a slightly decrease in their height to width ratio in water depths of less than 300-400 m, cone volcanism in those water depths apparently interacts with the water-air boundary and poses a hazard potential to the environment above the sea surface. Summarizing, this study presents a comprehensive study of the processes controlling the evolution of the Azorean oceanic islands and their submarine environment, as being the geodynamic and plate kinematic setting of the Archipelago, local tectonics, volcanism, bottom and density currents as well as destructive processes, like shelf erosion, subsidence and mass wasting.
Publications
-
2015. Morpho-structural evolution of a volcanic island developed inside an active oceanic rift: S. Miguesl Island (Terceira Rift, Azores). .Journal of Volcanology and Geothermal Research 301, 90-106
Sibrant, A.L.R., Hildenbrand, A., Marques, F.O., Weiss, B., Boulesteix, T., Hübscher, C., Lüdmann, T., Coasta, A.C.G., Catalão
-
2015. Submarine explosive volcanism in the southeastern terceira Rift / São Miguel Region (Azores). Journal of Volcanology and Geothermal Research 303, 79-91
Weiß, B., Hübscher, C., Wolf, D., Lüdmann, T.
-
2015. The Tectonic Evolution of the South-Eastern Terceira Rift / São Miguel Region (Azores). Tectonophysics 654, 75-95
Weiß, B., Hübscher, C., Lüdmann, T.
-
2016. Submarine sedimentation processes in the southeastern Terceira Rift / São Miguel region (Azores). Marine Geology 374, 42-58
Weiß, B., Hübscher, C., Lüdmann, T., Serra, N.
-
Crustal structure of the Eurasia-Africa plate boundary across the Gloria Fault, North Atlantic Ocean. Geophysical Journal International, Volume 209, Issue 2, 1 May 2017, Pages 713–729
Batista, L., Hübscher, C., Terrinha, P., Matias, L., Afilhado, A., Lüdmann, T.
