The evolution of Santa Maria Island in the context of the Azores Triple Junction

Abstract

is the oldest island in the Azores, formerly belonging to the Eurasia plate and currently the only one sitting on the Nubia Plate, thus sharing a geodynamic evolution with the Azores Triple Junction. It is therefore important to evaluate the effects of active tectonics on the evolution of Santa Maria, for example on its vertical movements. We present new stratigraphic, geomorphologic, structural and geochronological data from Santa Maria which shed further light on how a volcanic ocean island evolves in a tectonically active setting. Santa Maria island started with a first shield volcano (Old Volcanic Complex) that emerged ca. 6.0 Ma ago and was active until ca. 5.3 Ma. The short time span between the first and second shield volcanoes (ca. 0.3 Ma) and the preservation of only the western flank of this first shield volcano indicate an initial flank collapse at ca. 5 Ma. The collapse scar was covered by an eastwards dipping sedimentary complex (Intermediate Sedimentary Complex), with a likely tsunami deposit at the base. A second shield volcano (Young Volcanic Complex) rapidly grew on these sediments from 4.8 to 3.8 Ma, and the island subsided by more than 100 m. At 3.7 Ma, a second flank collapse occurred, as inferred from the missing summit and eastern flank. Volcanism then resumed (3.6 to 2.8 Ma), giving rise to Strombolian cones lying unconformably on the collapse scar, and conformable parasitic cones on the unaffected flank. Submarine lavas occurring at up to 200 m altitude with a youngest age of 3.0 Ma indicate major uplift of the island since, at most, that time. Here we interpret uplift as the result of rift flank uplift on the southern shoulder of the nearby Terceira Rift in the last ca. 1.5 Ma.

Island spider origins show complex vertical stratification patterns in Macaronesia

“…Specialization during speciation is more likely to happen in geologically older archipelagos (Gillespie et al, 2008), such as the Canary Islands (22 My) and Madeira (14 My), than in younger ones such as the Azores, which is, for the most part, less than 1 My old (Fernández‐Palacios et al, 2011; Marques et al, 2020; Triantis et al, 2012). Our results match this, with native non‐endemic species in the Canary Islands having higher vertical range than endemics.…”

A Global Database of Giant Landslides on Volcanic Islands

“…In the intervening period, important new research on giant landslides has been published from many parts of the Atlantic Ocean including Cape Verde (Martínez-Moreno et al 2018;Barrett et al 2020;Cornu et al 2021), the Azores (Hildenbrand et al 2018;Marques et al 2020Marques et al , 2021, the Canary Islands (Coello-Bravo et al 2020), and the Lesser Antilles (Solaro et al 2020) as well as the Bismarck Archipelago in the Pacific Ocean (Watt et al 2019). Moreover, the collapse of Anak Krakatau on 22 December 2018 stimulated much research (Williams et al 2019;Grilli et al 2019Grilli et al , 2021Hunt et al 2021;Cutler et al 2022) and it is anticipated that the collapse of Hunga Tonga-Hunga Haʻapai on 15 January 2022 will provide the impetus for many new studies.…”

Why do small volcanic ocean islands collapse? Lessons from Santa Maria Island, Azores Triple Junction

“…Similarly to other volcanic ocean islands (e.g. Hildenbrand et al, 2003;Ramalho et al, 2013;Marques et al, 2020b), Santa Maria experienced considerable vertical motions (Marques et al, 2020a), witnessed by submarine lava ows currently outcropping at ca. 200 m above sea level.…”