Natural Hazards (earthquakes, volcanic eruptions, tsunamis, landslides, coastal erosion, sea level changes, major space weather events…) can potentially affect millions of people and damage the economy of whole countries. They are a central research domain in the Earth sciences, where advances on academic research on the causes and consequences of natural phenomena as well as monitoring techniques and effective data analysis bring rapid and major benefits to the society. Despite much recent progress due to the development of techniques and simulations, geologists are still unable to predict precisely when and where an earthquake will happen and what its magnitude will be. Volcanoes, even when constantly monitored, remain also very enigmatic systems. In particular, forecasting of the timing and intensity of silicic eruptions remain out of reach. No scientifically developed country can afford to lag behind the others in this domain, in part for the sake of its international standing and responsibility towards its citizens and in part because natural disasters originating in one country are likely to affect neighbouring ones and can have impacts on a global scale. Furthermore, research in this domain heavily relies on permanent or semi-permanent multiparameter monitoring networks located in disaster-prone regions, where researchers and engineers remain close to potentially affected populations, which promotes trust in mitigation programs built and maintained on a long-term basis. From a general perspective, natural hazards are the end-result of large-scale geological processes that evolve over long time intervals and touch on almost all subdisciplines of the Earth Sciences in one way or another. Because of their potential impact on the industrial and social infrastructures as well as on health and sustainability issues, their study offers evident avenues for cross-disciplinary researches linked to Geography, Economy, Health, Social Sciences and Humanities.
Major challenges in the field of Natural hazards have been identified:
• to make the paradigms relating major natural hazards to plate tectonics evolve
(1) by developing new geophysical instruments and techniques to obtain a 3D multi-techniques characterisation and high frequency monitoring of the activity of natural systems, using innovative techniques such as muon tomography, correlation of optical images, sea-bottom optical seismometers, and/or combining geophysical and geochemical data,
(2) by collecting original geological records of their past activity, in particular by taking advantage of coupled on land and at sea studies.
• to decipher and model the coupling between underground magmatic plumbing systems and surface volcanic activity, e.g. the condition leading to an eruption rather than a magmatic intrusion, or the interpretation of the activity of a hydrothermal system in terms of eruptive potential.
• to characterize and model long period phenomena (such as slow earthquakes in Chile and LP earthquakes and tremors in Kamchatka) based on the constraints obtained thanks to the new numerical methods developed at IPGP to process large-data sets, and on quantitative physical models (rather than presently used qualitative models).
• to widen the impact of the results of fundamental research through exchanges with Humanities and Social Sciences, in particular to improve the management of natural risks and natural catastrophes, including the study of the impact of global change on the rate and intensity of natural phenomena (cyclones, landslides...) and coupled or chain-link processes (e.g. forcing of volcanic activity by extreme climatic events; triggering of eruptions by large magnitude distant earthquakes).