Description: The Cabo Verde Archipelago is related to a mantle plume located close to the rotational pole of the African Plate. It consists of islands and seamounts arranged in a horseshoe‐shaped pattern open to the west, thus forming two volcanic chains, each with a weak east‐west age progression. High‐resolution swath bathymetry of 12 Cabo Verde seamounts is used here to assign each seamount to its pre‐shield, shield or post‐shield evolutionary stage, respectively. The eastern seamounts exhibit degraded and partially eroded morphologies, and are mainly in their post‐shield stage. A new 40 Ar‐ 39 Ar date for Senghor Seamount at 14.872 ± 0.027 Ma supports old ages for the eastern seamounts. The western seamounts generally exhibit younger volcanic‐edifice‐construction morphologies, showing fresh effusive and explosive volcanics, including rarely observed deep‐water explosive volcanism in the Charles Darwin Volcanic Field. Furthermore, the two previously unknown seamounts Sodade and Tavares in the westernmost termini of both volcanic chains exhibit pristine volcanic morphologies, in agreement with present‐day volcanism and seismic activity recorded from the western seamounts. The islands and seamounts rest on three submarine platforms to the east, northwest and southwest, respectively. Taken together, the seamount and island data suggest a shift in igneous activity from the eastern to the other platforms at about 8–6 Ma. However, the complex evolution pattern for both volcanic chains includes the simultaneous occurrence of pre‐shield or shield edifices at any time, followed by erosional and rejuvenation stages. The new seamount data still demonstrate ongoing westward submarine‐growth in both volcanic chains. Plain Language Summary The Cabo Verde volcanic islands and seamounts are located in the central Atlantic Ocean, ∼570 km off the west coast of Africa. They form a horseshoe‐shaped archipelago with two volcanic chains, which were formed by the African plate moving very slowly over a mantle hotspot (the Cabo Verde Plume). Both the northern and southern volcanic chains show weak east‐to‐west age progressions from ∼26 million years to the present day. This study uses underwater topographic data and observations/rock sampling via remotely operated vehicles from 12 submarine volcanic seamounts, including two previously unknown seamounts, collected during four research cruises in the Cabo Verde Archipelago. Geomorphology is used to classify each seamount as being in its pre‐shield, shield or post‐shield evolutionary stage, respectively. Cabo Verde islands and seamounts rest on three submarine morphological platforms, reflecting westward jumps of the main igneous activity, and also confirming the westward migration of the Cabo Verde hotspot beneath both volcanic chains. Key Points We present bathymetrical maps of 12, in part previously uncharted Cabo Verde seamounts Geomorphology reflects various evolutionary seamount stages and relative ages. Four older seamounts indicate late Quaternary sea level lowstands Islands and seamounts rest on three morphological platforms, indicating westward jumps of the main igneous activity

Description: Highlights • Comprida Volcanic System ∼3180 cal yr BP eruption was the latest at Flores Island. • Eruptive style shifted from Hawaiian-Strombolian to phreatomagmatic. • All five (maybe six) phreatomagmatic craters were formed during a single eruption. • CVS eruption is nearly contemporary with a large gravitational flank collapse. • Future hazard assessments should consider the hydrologic characteristics of Flores. Abstract The stratigraphy and eruptive history of a volcanic system are key to forecast the timing and style of future eruptions. Flores is a small volcanic island in the Azores Archipelago with no record of eruptions since its settlement in the 15th century, although at least six eruptions are known to have occurred during the Holocene. Thus, Flores must be considered potentially active, and its volcanic hazard should not be disregarded. The most recent eruptions clustered at two centres of activity: the Funda Volcanic System (FVS) and the Comprida Volcanic System (CVS). Here, we reconstruct for the first time the eruptive history of CVS, the youngest volcanic system of Flores. Based on detailed tephrostratigraphic and geomorphological work, combined with radiocarbon dating and glass shard geochemistry, we show that – despite featuring five (maybe six) phreatomagmatic craters – CVS was formed in a single volcanic eruption at ∼3180 cal yr BP. This eruption started with Hawaiian-style lava fountaining followed by Strombolian activity, dispersing tephra fallout across the central part of the island. Lava flows were also emitted during the initial phase, which drained to the west and cascaded over the older deposits of the massive slump of Fajãzinha–Fajã Grande, and possibly reached the coastline to form the Fajã Grande lava delta. The initial magmatic phase was followed by phreatomagmatic explosions that formed several maars and tuff rings. Hence, groundwater played an important role in the eruption by transforming a mild Hawaiian-Strombolian eruption into a highly explosive phreatomagmatic event, possibly due to oscillations in the eruption rate. The occurrence of a large landslide contemporary to the eruption, raises the possibility of a combined threat. A new and more robust volcanic hazard assessment for the island involving scientists and civil protection authorities is desirable.

Description: Lacustrine sequences from active volcanic settings usually hold a rich and continuous record of tephra layers, providing a critical source of information to reconstruct a most complete eruptive history of a region. Lake sedimentary records on volcanic islands are particularly useful as the typical small size of these islands and their steep subaerial and submarine slopes lead to a lower preservation of potential erodible pyroclastic deposits. Here we explore the lacustrine sedimentary record of Lagoa da Lomba, a crater lake in the central upland area of Flores Island (Azores), to gain insight into the recent eruptive history of this island. The strategic location of Lagoa da Lomba, half distance between the two clusters of recent volcanic activity of the island, together with its long-lasting record, back to 23.52 cal kyr BP, makes this lake a privileged site to investigate the Holocene volcanic history of Flores. Based on a detailed stratigraphic characterization of sediments from a lake transect of three cores, supported by glass shard geochemistry and radiocarbon dating, we recognized four Holocene eruptive events taking place between 6.28 and 2.36 cal kyr BP, demonstrating that the Holocene volcanic activity at Flores Island may have lasted longer than previously reported. Glass shard geochemistry from the different tephra layers suggests three populations, basaltic to trachybasaltic in composition, where the last eruption is the least evolved endmember. Two of the four eruptive events correlate with subaerially-exposed pyroclastic sequences, in terms of stratigraphy and geochemistry. The most recent event recorded at Lagoa da Lomba was constrained to 3.66 – 2.36 cal kyr BP and linked to an eruption sourced from Lagoa Comprida Volcanic System. The second most recent eruptive event was sourced from Lagoa Funda Volcanic System and dated at 3.66 cal kyr BP. Our observations show that Flores experienced vigorous volcanic activity during the Late Holocene. Therefore, contrary to what is assumed, the possibility of future eruptions should be properly considered, and the volcanic hazard here should not be underestimated. Moreover, we highlight the importance of tephrostratigraphy in recent lake sediments to reconstruct past volcanic activity, especially at small volcanic islands, such as Flores, where exposure is poor due to erosion within the limited subaerial area and the dense vegetation.

Description: Highlights • Funda Volcanic System produced at least 3 eruptions over a period of 〈200 years. • Volcanism was longer and more recurrent than previously reported. • Eruptive styles range from Strombolian (mild and violent) to phreatomagmatic. • Magma/groundwater interactions may have led to rapid changes in eruptive style. • Future hazard assessment need to effectively consider magma/groundwater interactions. Monogenetic volcanoes occur in many different geotectonic settings and are usually small and short-lived. They can experience a variety of eruptive styles, even during the same eruption. In monogenetic volcanic fields, volcanism usually migrates to different locations over time, making volcanic hazard assessment very challenging. The eruptive history of a volcanic region, including the size, style, and location of previous eruptions, provides valuable information to help predict the behaviour of future volcanic events and their associated hazards. Here, we reconstruct for the first time the eruptive history of the Funda Volcanic System (FVS), one of the most recent (∼3 ka) monogenetic eruptive centres of Flores Island (Azores), based on a detailed tephrostratigraphic work coupled with geochemical analysis of glass shards and radiocarbon dating. We identified at least three volcanic events at FVS spaced by time intervals of ∼100 yr. The first event (3430 cal yr BP) was a small Strombolian eruption, the second event (3330 cal yr BP) started as a violent Strombolian eruption and may have ended as phreatomagmatic, and the third event (3250 cal yr BP) was exclusively phreatomagmatic. Our results demonstrate that volcanism at the FVS was more prolonged and recurrent than previously reported. Moreover, we show that the FVS experienced different eruptive styles in a short timeframe, ranging from small basaltic eruptions to violent explosive phreatomagmatic events. Such diversity of eruptive styles results in different volcanic products, which have different hazard implications. Our new results contribute to the knowledge of the recent volcanic activity of Flores Island, and we anticipate them to be of paramount importance for future volcanic hazard assessment studies.

Description: The multibeam data set was acquired in 2021 during the Instituto Hidrográfico cruise HI 09A/20 under the guideance of Captain Franco Leitão, and is originally available through the website (https://gridmarcv.hidrografico.pt/) but also at the IHO Data Centre for Digital Bathymetry (https://www.ngdc.noaa.gov/iho/). The hydrographic survey was carried out with the NRP ALMIRANTE GAGO COUTINHO, equipped with the EM 710 and EM120 multibeam sounding systems. Positioning was assured by a SEAPATH 330+ system from SMF KONGSBERG EM710/EM120, GNSS data. Depth values are referred to ZH (0.80m from the Average Level adopted in Cape Verde). Information on data processing is unavailable as we are not the orignial authors of this data set but re-issue it by permission. The original ungridded data set contained in the .txt file was gridded to a 25m cell size using GlobalMapper, and is submitted here as an ascii grid file.