Anthony Hildenbrand

• PhD, HDR
• Researcher at French National Centre for Scientific Research

Global climate variations (e.g., during glacial-interglacial transitions) induce local climatic effects such as temperature and precipitation changes, significantly impacting the chemical and physical degradation of volcanic islands. Conversely, the weathering of volcanic rock, especially on volcanic islands, consumes CO2 , thus impacting its conce...

The weathering of basaltic rocks, especially on volcanic islands, plays a crucial role in global carbon cycling. In these environments, intense precipitation and frequent exposure of fresh rocks accelerate weathering processes, thus favoring the uptake of atmospheric CO2. While most estimates of weathering rates derive from river chemistry, soils a...

Triple junctions, where three tectonic plates meet, play a critical role in geodynamics. The Azores Triple Junction is critical in the study of triple junctions, challenging traditional models of triple junction stability. Unlike the established rift-rift-rift framework, the Azores Triple Junction exhibits notable complexities, including a sigmoida...

Mass controls two major processes in volcanic islands: large-scale collapse and vertical movements. Therefore, large islands like Hawaii are gradually subsiding and have undergone massive landsliding. What if the mass is much smaller, and there is good evidence that the vertical movement is more complex than simple loading-related subsidence? Here,...

Mass controls two major processes in volcanic islands: large-scale collapse and vertical movements. Therefore, large islands like Hawaii are gradually subsiding and have undergone massive landsliding. What if the mass is much smaller, and there is good evidence that the vertical movement is more complex than simple loading-related subsidence? Here,...

The most important form of plate evolution occurs where three tectonic plates meet, a triple junction ¹ (TJ). Ridge-ridge-ridge (RRR) TJs are unique because they are stable at all ridge configurations and spreading velocities ¹ . This idealised and simplified RRR TJ with three straight rifts is challenged here by showing that it does not apply if a...

The late Quaternary paleoclimate of the North Atlantic region has been widely studied, but the local terrestrial response to broader climatic variations remains underexplored. The Azores Archipelago, influenced by the North Atlantic Oscillation (NAO) and the Azores High, is a strategic target to investigate such interactions. Here, paleosols develo...

Large-scale flank collapses are one of the main hazards associated with the evolution of volcanic islands. Precisely dating such events is critical to evaluate the frequency of destabilization episodes and further assess the triggering mechanism(s) associated with internal and/or external factors, such as volcano dynamics, regional tectonics, and g...

Volcanic islands evolve through complex interactions between volcano growth and surface processes. Climate changes impact the physical and chemical processes that drive weathering and denudation. While global paleoclimate has been extensively studied for the late Quaternary, elucidating the local climatic response to global forcing on such islands...

Full data set associated with the thesis project "Climatic and landscape evolution of the Azores over the past million years" by Francisco Hevia-Cruz, under the direction of Anthony Hildenbrand (CNRS GEOPS, Université Paris-Saclay) and Nathan D. Sheldon (University of Michigan), at Université Paris-Saclay. It corresponds to a single file with six s...

Volcanic ocean island collapse is a gravitational process, which means that mass is a key variable. Here we show that small volcanic islands (small mass) usually considered stable can undergo full flank collapse (i.e. full flank plus summit), and we also evaluate the most likely collapse mechanisms by numerical modelling. Santa Maria Island (Azores...

Paleosols (PSs) contain valuable information about the climatic conditions under which they formed and constitute an outstanding archive of past weathering processes. Nevertheless, paleosol dating over most of the Quaternary remains challenging. Volcanic environments are unique sites for such purposes, as precise radiometric age determination can b...

Climatic variations impact landscape processes on volcanic islands in various ways. While glacial periods and low sea level may favor canyon deepening by enhanced river incision, wetter and warmer interglacial stages favor rock weathering and soil formation, promoting fast landscape evolution. On such volcanic islands, paleosols (PSs) contain valua...

Volcanic ocean island collapse is a gravitational process, therefore mass is a key variable. Based on this premise, islands much smaller than Hawaii are believed to be not prone to collapse. Here we show that they can collapse, and more than once, like in Santa Maria Island (Azores), 170 times smaller than Hawaii, as inferred from onshore data and...

Modeling of tsunami waves generated by subaerial landslides is important to provide accurate hazard and risk assessments in coastal areas. We perform small-scale laboratory experiments where a tsunami-like wave is generated by the gravity-driven collapse of a subaerial granular column into water. We show that the maximal amplitude reached near-shor...

The age of breakup which formed the Central-North Atlantic has been debated for many decades and is still subject to debate: from ca. 150 Ma to 110 Ma. To address this issue, we have carried out a thermochronological study of the eastern margin of the rifted Iberia-Newfoundland sector. New apatite fission-track (AFT) data acquired on samples from t...

Exhumation of the roots of collapsing orogens is a key process in the evolution of mountain belts, which is critical for the understanding of orogenic cycles. From new structural analyses, KAr and ⁴⁰Ar/³⁹Ar on muscovite, biotite and K-feldspar, and available UPb ages, we constrain the cooling and exhumation history of granitic batholiths from the m...

The Pico-Faial ridge is a steep WNW-ESE volcanic ridge that has developed within the Nubia-Eurasia diffuse plate boundary, close to the Azores Triple Junction. The ridge comprises two islands, Pico and Faial, separated by a shallow (< 100 m depth) and narrow (< 8 km) channel. Despite some similarities, the two islands show contrasting features stil...

We present paleomagnetic and geochronological data of twenty-five stacked lava flows from São Miguel Island (Azores) that were emplaced during the last geomagnetic reversal (Matuyama-Brunhes, M-B). The characteristic direction of natural remanent magnetization was isolated through alternating field and/or thermal demagnetization. From bottom to top...

Santa Maria 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 movemen...

Dated paleosea level markers and eustatic sea level changes are necessary but not sufficient information to calculate vertical motion rates on oceanic islands. Therefore, we use a procedure in which we work progressively back in time to incorporate the more recent vertical motion rates implied by the youngest paleoshorelines into the vertical motio...

The target of this study is the Fogo Island in Cape Verde, where the hazards (caldera and/or flank collapse) and the timing (120 ka or younger?) are still controversial. Using high-resolution DEM, field geological and structural analysis, and high-precision K-Ar dating, we produced an age-calibrated volcanic stratigraphy of Fogo’s summit (Chã das C...

Absolute dating is needed to check and calibrate the relative Martian chronology presently available from meteoritic crater counting. For such purpose, a new analytical system (KArMars) has been developed to experiment the feasibility of in-situ K-Ar for future landing planetary missions. It consists in a laser ablation-based system built to vapori...

We report a new paleomagnetic and rock magnetic volcanic record of the Matuyama-Brunhes (M-B) transition in a sequence of 28 lava flows from the Azores Island. We sampled a 100-m thick succession of lavas incised by a deep creek. More than 250 paleomagnetic samples were analyzed using both alternating field up to 120 mT and thermal stepwise demagne...

Small intra-plate volcanic islands (total height above seafloor <2500 m) have been considered gravitationally stable. Topographic, stratigraphic, structural and new K/Ar data show that the small island of Flores (Azores) is strongly asymmetric and made up of nested volcanic successions. Along the northwestern coastline, ca. 1.2 Ma lava flows are in...

The S. Jorge Island in the Azores lies on a peculiar setting, the southern shoulder of the Terceira Rift (TR), which raises a series of questions that we address in this study. We first established the main volcanic stratigraphy by recognizing, in the field, the main unconformities/discontinuities and their meaning (major erosion surfaces and fault...

The Portuguese Submission for the Extension of the Continental Shelf is being considered by the Commission on the Limits of the Continental Shelf (CLCS) since August 2017, to assess the scientific arguments of the coastal State. During the extension project was essential to identify, in the continental margin the natural components. The Task Group...

The morphology of volcanic oceanic islands results from the interplay between constructive and destructive processes, and tectonics. In this study, the analysis of the paleomagnetic directions obtained on well-dated volcanic rocks is used as a tool to assess tilting related to tectonics and large-scale volcano instability along the Pico-Faial linea...

New geochemical, isotopic (Sr-Nd-Hf-Pb) and K-Ar data, are presented here on samples from the Southern Azores Seamount Chain (SASC) located south of the Azores Plateau. The SASC also includes the Great Meteor, Small Meteor and Closs seamounts, morphologically connected by a saddle at − 4100 m deep. We conclude that the SASC are characterized by a n...

The Southern Azores Seamount Chain (SASC) is a group of large seamounts located south of the Azores Plateau and east of the Mid-Atlantic Ridge (MAR) and part of the natural prolongation of the Azores land mass. The SASC, including the Great Meteor Seamount (aprox. 1000km south of São Miguel), is rooted on a flat, gently SE dipping Terrace, surround...

The research program aimed on the in-depth understanding the volcano-tectonic evolution of the Azores plateau and associated geo-hazards such as submarine landslides and volcanic surges. Oceanic plateaus like the Azores plateau are large areas of anomalously thick crust forming large bathymetric swells in the ocean basins and their petrological for...

The critical taper theory of Coulomb wedges has been classicaly applied to compressive regimes (accretionary prisms / fold-and-thrust belts), and more recently to gravitational instabilities. Following the initial hypothesis of the theory, we provide an alternative expression of the exact solution for a non-cohesive wedge by considering the balance...

Several processes concur to shape an oceanic volcanic island, in particular the insular shelves, but the dominant process will be the one with the highest rate for a given period of time. Therefore, one has to estimate rates in order to conclude for the dominant process. We take advantage of the contrasting tectonic settings of two islands in the A...

The evolution of hyperslow oceanic rifts, like the Terceira Rift (TR) in the Azores, is still poorly understood. Here we examine the distribution of strain and magmatism in the portion of the TR making up the Nubia-Eurasia plate boundary. We use São Miguel Island because it stretches most of the TR width, which allows to investigate the TR's archit...

In Sibrant et al. (2014), we reconstructed the evolution of Graciosa Island (Azores). We extensively discussed the nature and the meaning of the destruction episodes, either tectonics or gravitational, and concluded that the island has evolved through major landslides. In their comment, Quartau et al. conclude that: (1) “Sibrant et al. (2014) is ba...

The interpretation of high-resolution topography/bathymetry, GPS and InSAR data, and detailed structural geology indicate that: (1) Terceira developed at the intersection of two major volcano-tectonic lineaments: WNW-ESE (local TR’s direction) and NNW-SSE (submarine chain of volcanoes, here firstly recognized and coined Terceira Seamount Chain). (2...

The growth and decay of oceanic volcanoes developed close to plate boundaries are intrinsically related to a competition between construction and destruction processes, partly controlled by tectonic strain and stresses. From morphologic, stratigraphic, tectonic and new high-precision K-Ar data, we present a comprehensive picture of the volcano-tect...

We present here a digital methodology aimed at identifying the morphometry of monogenic volcanic cones including edifice height, slope angle, and volume. We recognize more than 800 monogenic volcanic cones from the Harrat Ash Shaam volcanic province (HASV, northern Arabian Plate) to the north of the Arabian plate by using Landsat7 Enhanced Thematic...

The study of volcanism near unstable plate triple junctions (TJs) offers a unique opportunity to investigate the interactions between mantle dynamics and lithospheric deformation in relation to short-term plate reconfiguration. From combined geochronological and geochemical analyses on Terceira, S. Jorge and Faial volcanic islands, we evidence cont...

The study of volcanism near unstable plate triple junctions (TJs) offers a unique opportunity to investigate the interactions between mantle dynamics and lithospheric deformation in relation to short-term plate reconfiguration. From combined geochronological and geochemical analyses on Terceira, S. Jorge and Faial volcanic islands, we evidence cont...

With very few exceptions, M > 4 tectonic earthquakes in the Azores show normal fault solution and occur away from the islands. Exceptionally, the 1998 shock was pure strike-slip and occurred within the northern edge of the Pico-Faial Ridge. Fault plane solutions show two possible planes of rupture striking ENE-WSW (dextral) and NNW-SSE (sinistral)....

The northern part of the Arabian plate (NAP) has been the locus of widespread cenozoic volcanism, which has been linked recently to two contrasted styles of lithospheric deformation: (1) stretching in the North close to the Arabian-Eurasian collision and (2) rotational tectonics further south [1]. Recent whole-rock geochemical data suggest that the...

Widespread lava fields in the northern part of the Arabian platform are the subject of an open geodynamic debate on the origin of the intraplate volcanism. We present new K–Ar ages and whole-rock geochemical data for lava flows from Syria, which allow us to propose a new model of volcano-tectonic evolution highlighting how tectonics have controlled...

The concept of an 'Azores mantle plume' has been widely debated, and the existence of an Azores hotspot questioned. In an effort to shed new light on this controversy, we present He isotope and major, trace and volatile element compositions for basaltic scoriae from five monogenetic cones emplaced along the fissure zone of Pico Island, the youngest...

Large-scale flank collapses are common in the geological evolution of volcanic ocean islands in the Atlantic. To date, catastrophic lateral collapses in the Azores Islands have been difficult to identify, leading to suggestions that a lack of events may relate to the relatively small size of the islands. Here we show evidence for two major collapse...

The evolution of volcanic islands is generally marked by the interplay between construction and destruction processes. Large-scale flank collapses episodes, especially, constitute a major threat, because they can generate fast-running debris-avalanches and trigger destructive tsunamis. The Azores islands are located on the triple junction between N...

We use GPS, bathymetric/structural, and seismic data to define the pattern of present deformation along the northern half of the Azores plateau, where the Nubia-Eurasia plate boundary terminates at the axis of the Mid-Atlantic Ridge (MAR). New and existing campaign GPS velocities from the Azores islands reveal extension oblique to a series of en éc...

Geological mapping, accurate K/Ar dating and geochemical analyses of lavas allow a detailed reconstruction of the geological history of Tahiti-Nui Island (French Polynesia). The exposed volcanic activity is first characterized by the construction of a main shield from 1.4 Ma to 870 ka, with a maximum aerial eruptive rate around 2 km3/kyr. Lavas fro...

Giant landslides are an important part of the evolution of most intra-plate volcanic islands. They often proceed in catastrophic events, likely to generate voluminous debris avalanches and eventually trigger destructive tsunamis. Although knowledge of the timing of their recurrence is a key factor regarding the hazard assessment in coastal environm...

Azores intra-plate oceanic basalts are thought to be a typical example of hot-spot ridge interactions. Volatiles (in particular CO2 and H2O) represent key parameters at each step of magma production, differentiation and eruption. We report here the first complete data set on major, trace and volatile elements, together with He isotopes for basaltic...

The Harrat Ash Shaam volcanic province (HASV) is the largest volcanic field in the Arabian plate. It developed during the Cenozoic close to the southern part of Dead Sea fault system and has been linked to the tectonic evolution of the Red Sea rifting since the early Oligocene. The HASV is an ideal environment to study volcanism adjacent to a strik...

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 aimed at recovering the successive stages of development of Faial (Azores) during the last 1 Myr. Using high-resolution digital elevation model (DEM), new K/...

We report evidence for ongoing lateral slump of part of the southeastern flank of the Pico volcanic ridge in the Azores. Data from a high-resolution digital elevation model, field work, GPS, and radar interferometry show that: (1) the slumping sector is several cubic kilometers in size; (2) the structure involves several curved scars with normal fa...

We present a palaeomagnetic study on 38 lava flows and 20 dykes encompassing the past 1.3 Myr on S. Jorge Island (Azores Archipelago—North Atlantic Ocean). The sections sampled in the southeastern and central/western parts of the island record reversed and normal polarities, respectively. They indicate a mean palaeomagnetic pole (81.3°N, 160.7°E, K...

Large sector collapses are a major component of oceanic islands evolution. Here we show that voluminous events such as the Icod landslide on Tenerife (Canary Islands) cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr. Instant...

We report evidence for ongoing lateral slump of part of the southeastern fl ank of the Pico volcanic ridge in the Azores. Data from a high-resolution digital elevation model, fi eld work, GPS, and radar interferometry show that: (1) the slumping sector is several cubic kilometers in size; (2) the structure involves several curved scars with normal...

Volcanic ocean islands are particularly prone to flank instability. Episodes of flank destabilization can remove great amounts of volcanic material, either as creeping rotational landslides along a deep detachment, or in the form of fast running debris avalanches produced by the sudden flank rupture. Based on high-resolution DEM, fieldwork, GPS, In...

The Cantal strato-volcano is the largest eruptive complex of the French Cenozoic volcanic province. It has been active during the Upper Miocene and has been characterized by the emplacement of voluminous volcanoclastic breccias, which the origin and the significance remain controversial. Field observations, coupled with new K-Ar ages, allow us to r...

Os isotope evolution of an oceanic intra-plate volcano: Tahiti-Nui (Society Islands, French Polynesia) F. Nauret1, K. David1, A. Gannoun1, A. Hildenbrand2, P-Y.Gillot2, G. Delpech2, P.Schiano1 1 LMV, Université Blaise Pascal, UMR 6524, 5, rue Kessler. 63038 Clermont-Ferrand. France. F.Nauret@opgc.univ-bpclermont.fr 2 IDES, Université Paris-Sud, U...

The Azores Archipelago is located in the North-Atlantic Ocean, near the triple junction between the American, the Eurasian and the Nubian lithospheric plates. It comprises nine active volcanic islands which have developed on the eastern and western flanks of the Mid-Atlantic Ridge (MAR). The area is affected by active faults responsible for recurre...

New K/Ar dating and geochemical analyses have been carried out on the WNW–ESE elongated oceanic island of S. Jorge to reconstruct the volcanic evolution of a linear ridge developed close to the Azores triple junction. We show that S. Jorge sub-aerial construction encompasses the last 1.3 Myr, a time interval far much longer than previously reported...

Giant landslides affecting volcanic islands can generate voluminous debris-avalanches (DA) and provoke destructive tsunamis. A number of triggering factors have been proposed over the past twenty years but their mutual interactions are still controversial. In addition, the dynamic behavior of submarine DA remains largely unknown, though it constitu...

Giant landslides and resulting tsunamis represent the main geologic hazards linked to volcanic island evolution. From offshore and onland studies, flank failures have been identified around numerous islands, in most geodynamic contexts. However, the triggering conditions are still poorly understood and several causes may act simultaneously to reach...

A quantitative geomorphological study has been made on 27 river basins in Tahiti-Nui volcanic island (French Polynesia) to reconstruct the erosional evolution of a young oceanic island subjected to heavy tropical rainfall. Tahiti-Nui is composed of a main shield volcano cut by two huge landslides on each side of a main E–W rift zone. The northern l...

Giant landslides and resulting tsunamis represent the main geologic hazards linked to volcanic island evolution. From bathymetric data and on-land geological studies, flank failures have been identified around numerous volcanic islands, in most geodynamic contexts. However, the enabling and triggering conditions are still poorly understood and seve...

We are presenting a new set of K/Ar ages and geochemical analyses obtained on deep-sea samples dredged in 1999 on several seamounts of the Cook-Austral volcanic chains in the Pacific Ocean. The new geochemical results, together with published data on island samples, allow us to reveal a time evolution of the mantle source composition as well as an...

A bathymetric analysis of the northern flank of Tahiti-Nui (French Polynesia) confirms the existence of a major catastrophic landslide event during its eruptive history, as previously proposed by Gillot et al. (1993). The related debris-avalanche has a volume estimated about 800 km^3, and extends as far as 50 km to the North. It is overlain by subs...