arXiv subjects

Julien Gargani

Publications and source records attributed to Julien Gargani.

9 recordsLinked to original sources

arXiv2026

Analyzing the role of tensile and hybrid fractures on the max-imum relief topography

Slope stability description through mechanical laws has important implication for Earth morphology understanding and risk assessment. Previous researches have showed that shear, tensile, and hybrid fractures can be observed experimentally and in the field, but their descriptions by a single equation is still an open debate. Fracture envelope able to describe contemporaneously these three fracture modes differ signif-icantly from the Mohr-Coulomb law. Despite the need to apply such a law at all scales, from the laboratory to the mountain range, the fracture criterion that characterizes all types of fractures is rarely used in geotechnical engineering and geological investiga-tions. In order to analyze the stability thresholds of large-scale relief, the current work examines the effects of considering the Griffith criterion with a variable rock traction instead of the Mohr-Coulomb law using a modelling approach. The difference esti-mated on maximum relief using these two different rupture criterions could be of the same order than the one caused by geological phenomena, such as with or without seismic activity, or from the one caused by the destabilization processes (tilting vs. landslide). When compared to the modified Griffith criterion, the Mohr-Coulomb law tends to overestimate the maximum escarpment height. The results are examined in relation to the Carrara marbles, which serve as a case study for the theoretical frame-work.

physics.geo-ph↗

arXiv2024

The impact of climate and wealth on energy consumption in small tropical islands

Anthropic activities have a significant causal effect on climatic change but climate has also major impact on human societies. Population vulnerability to natural hazards and limited natural resources are deemed problematic, particularly on small tropical islands. Lifestyles and activities are heavily reliant on energy consumption. The relationship between climatic variations and energy consumption must be clearly understood. We demonstrate that it is possible to determine the impact of climate change on energy consumption. In small tropical islands, the relationship between climate and energy consumption is primarily driven by air conditioner electricity consumption during hotter months. Temperatures above 26{\deg}C correlate with increased electricity consumption. Energy consumption is sensitive to: (1) climatic seasonal fluctuations, (2) cyclonic activity, (3) temperature warming over the last 20 years. On small tropical islands, demographic and wealth variations also have a significant impact on energy consumption. The relationship between climate and energy consumption suggests reconsidering the production and consumption of carbon-based energy.

physics.soc-ph↗

arXiv2023

Relative sea level and coastal vertical movements in relation with volcano-tectonic processes in Mayotte

During the last 10 kyr, significant subsidence and uplift occurred on Mayotte Island in the Comoros archipelago, but the role of volcanic processes in Holocene vertical movements has been neglected. Here, we show that an abrupt subsidence of 10 m occurred 9.3 kyr ago and then an uplift of the same amplitude occurred at a rate of 9 mm/yr from 8.1 kyr to 7 kyr ago, and we compare the relative sea level of Mayotte with a reference sea level curve. Using a modeling approach, this study shows that an increase and a decrease in pressure in a deep magma reservoir was responsible for the ~10 m subsidence and the 10 m uplift, whereas the loading by new volcanic edifices has caused the subsidence that has occurred during the past 6.1 kyr. The surface movement was caused by pulses from the deep mantle that were probably related to superplume activity.

physics.geo-ph↗

arXiv2023

Influence of relative sea-level rise, meteoritic water infiltration and rock weathering on giant volcanic landslides: theory and real cases

Recent studies have shown that giant landslides seem to be correlated with climatic variations. Nevertheless, the precise processes that are involved in this phenomenon need to be better constrained. In this study, the causes of giant landslides are investigated using a modeling approach. Here, we show that the effect of meteoritic water infiltration could be discriminated from that of sea-level rise on triggering paleolandslides. It is possible to identify the cause of coastal paleolandslides based on the age of occurrence and comparison with climatic signals when glacial maxima are more humid than during interglacial times, as in Polynesia and East Equatorial Africa, but not in other cases (Caribbean, Indonesia). The role of pore pressure variations and sea-water loading variations has been discussed. The interaction between the relative sea-level rise, preexisting relief and deep weak structure due to the presence of highly weathered lavas may trigger the conditions for a large landslide. Highly weathered lavas have very low friction angles at depth in volcanic islands. When volcanoes are still actives, pressure variation of the magma chamber caused by sea-level lowering is expected to play a significant role in destabilization of the relief. Competing processes in real cases cause difficulties to discriminate between these processes.

physics.geo-ph↗

arXiv2022

Relative Sea Level and Abrupt Mass Unloading

Relative sea level records climatic change as well as vertical land movement. In Barbados, uplift variation is necessary to interpret one of the most complete coral reef records. Here we show that an abrupt mass unloading of 30 km3 caused an uplift variation of ~0.45 mm/yr using a modelling approach. Simulations have been conducted for different volumes and elastic thicknesses. Isostatic adjustment in relation with an abrupt mass unloading explains the observed uplift rate increased from 0.34 mm/yr to 0.8 mm/yr that occurred 11.2 kyr ago. The reconstructed sea-level curve highlights a sea-level jump of 4.8 m, with a delay of 150 yr from the termination of Younger Dryas cold event and 300 yr before the abrupt mass unloading. This sea-level jump corresponds to meltwater pulse MWP-1B and is not an artefact. A stagnation of 500 yr occurred from 12 to 11.5 kyr BP. Relative sea level records are useful to detect past landslides and erosion. Accurate analysis and reconstruction of sea-level permits to determine sea-level abrupt rise caused by climate warming during the last thousand years.

physics.geo-ph↗

arXiv2022

Isostatic Modelling, Vertical Motion Rate Variation and Potential Detection of Past-Landslide in the Volcanic Island of Tahiti

Intraplate volcanic islands are often considered as stable relief with constant vertical motion and used for relative sea-level curves reconstruction. This study shows that large landslides cause non-negligible isostatic adjustment. The vertical motion that occurred after landslide is quantified using a modelling approach. We show that a giant landslide caused a coastline uplift of 80-110 m for an elastic thickness of 15 km < $T_e$ < 20 km in Tahiti. Theoretical cases also reveal that a coastal motion of 1 m occurred for a landslide involving a displaced volume of 0.2 $km^3$ and influence relative sea-level reconstruction. In Tahiti, a change in the subsidence rate of 0.1 mm/yr (from 0.25 mm/yr to 0.15 mm/yr) occurred during the last 6 kyr and could be explained by a landslide involving a minimum volume of 0.2 $km^3$, $6 \pm 1$ kyr ago.

physics.geo-ph↗

arXiv2022

Resilience and inequality growth monitoring after disaster using indicators based on energy production

The estimation of resilience and the determination of inequality growth after a disaster is often difficult. In this study, specific indicators were developed to analyze resilience, and the trajectories of resilience were compared. Energy production is relevant for describing variations in social and economic activities. This indicator was applied to a case study of a natural disaster, that is Hurricane Irma in 2017. The hurricane caused fatalities and destruction in the Caribbean islands of Saint Martin and Saint Barthelemy, which are two French overseas territories. Energy production after Hurricane Irma exhibited a significant decrease due to the destruction of the electricity network as well as perturbations in economic and social activities. The energy production restoration rate was higher in Saint Barthelemy than in Saint Martin. The electricity restoration rate after a disaster was almost constant. However, the energy production 18 months after Hurricane Irma was identical to that before Hurricane Irma in Saint Barthelemy; this was not the case in Saint Martin. During resilience, an increase in the gap between energy production in Saint Barthelemy and Saint Martin was observed. This study indicated that this gap represents an inequality growth between Saint Barthelemy (gross domestic product (GDP) of 40 000 euros/inhabitant) and Saint Martin (GDP of 16 600 euros/inhabitant). The indicators emphasized that inequality growth after natural disasters favors less vulnerable and more resilient territories. The number of inhabitants must be considered during indicator construction to avoid any bias.

physics.soc-ph↗

arXiv2021

Impact of major hurricanes on electric energy production

After major hurricanes, electric production is significantly reduced owing to not only electric infrastructure destruction, but also the economic crisis associated with damage to private and public activities. The full restoration of the electric infrastructure is not always simultaneously performed with the full restoration of electric production. Here, we describe the electric production curves for the islands of Saint-Martin, Saint-Barthelemy, and Puerto Rico in the Caribbean, where two major hurricanes occurred in 2017. After the major hurricanes, the electric energy production was characterised by a slow recovery followed by a stable phase during several months, corresponding to approximately $75\%$ of the initial electric production. A resilience time of several months (1 month $< t_s <$ 5 months) is necessary to attain the new electric energy production equilibrium $E_{is}$, which is lower than the initial electric energy production $E_i$. The reduction in electric energy consumption per capita is of $20-25\%$. In Saint-Martin, during the post-hurricane stable phase, the electric production was only approximately $60\%$ of the initial electric energy production instead of $75\%$. The reduction of 15 percent in the electric production of Saint-Martin after Hurricane Irma could be attributed to the migration of approximately 8 000 inhabitants (approximately $23\%$) outside the island. This approach makes it possible to anticipate the production of electricity during several months after a major hurricane in the Caribbean islands.

physics.soc-ph↗

arXiv2020

Mobility and dynamics of Giant landslides

The rarity of large landslides reduces the number of observations and hinders the understanding of these phenomena. Runout distance was used here to determine whether the large landslide deposit formed several thousand years ago in northern Tahiti was caused by a single or multiple events. Using modelling to quantify the dynamics of this event suggested that a single event or a small number of events (n<10) were responsible, and that the maximum slide velocity was high (>125 m/s) under partially submarine conditions. Such submarine propagation favoured a slower dynamic but a longer runout. The effective basal friction under submarine conditions ranged from 0.2 < $μ$ < 0.3.

physics.geo-ph↗