Description: Hydro‐fracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume. Both observations and theoretical models show that, if the fluid volume is larger than a critical value, pockets of fluid can propagate large distances in the Earth's crust in a self‐sustained, uncontrolled manner. Existing models for such critical volumes are unsatisfactory, most are two‐dimensional and depend on poorly constrained parameters (typically the fracture length). Here we derive both analytically and numerically in three dimensions scale‐independent critical volumes as a function of only rock and fluid properties. We apply our model to gas, water and magma injections in laboratory, industrial and natural settings, showing that our critical volumes are consistent with observations and can be used as conservative estimates. We discuss competing mechanisms promoting fracture arrest, whose quantitative study could help to assess more comprehensively the safety of hydro‐fracturing operations.

Description: Forecasting and early warning systems are important investments to protect lives, properties and livelihood. While early warning systems are frequently used to predict the magnitude, location and timing of potentially damaging events, these systems rarely provide impact estimates, such as the expected amount and distribution of physical damage, human consequences, disruption of services or financial loss. Complementing early warning systems with impact forecasts has a two‐fold advantage: it would provide decision makers with richer information to take informed decisions about emergency measures, and focus the attention of different disciplines on a common target. This would allow capitalizing on synergies between different disciplines and boosting the development of multi‐hazard early warning systems. This review discusses the state‐of‐the‐art in impact forecasting for a wide range of natural hazards. We outline the added value of impact‐based warnings compared to hazard forecasting for the emergency phase, indicate challenges and pitfalls, and synthesize the review results across hazard types most relevant for Europe.

Description: Erta Ale Volcano erupted on 16 January 2017 in a difficult‐to‐access terrain in the Erta Ale volcanic range in Ethiopia. Like many other rifting ridge volcanoes, little is known about the properties of the deep magma plumbing system. Here, we analyze interferometric synthetic aperture radar data from different satellites between late January 2017 and May 2019 to study the ground deformation after the start of the intrusion to infer the possible geometry and volume change of the magma reservoir that fed the eruption. We identified volcano‐wide subsidence of up to 9 cm and horizontal contraction of up to ~5 cm that extend from Erta Ale to neighboring volcanoes. The modeling results suggest that an off‐rift NE‐SW elongated mid‐crustal source is required to explain the observed volcano‐wide deformation, but the depth is poorly constrained and the shape is complex. We suggest the presence of vertical interactions between stacked mid‐crustal magma sources. Our study demonstrates that a considerable volume of melt could have been stored in mid‐crustal magma reservoirs within the slow‐spreading Erta Ale Ridge to facilitate recent volcanic activity.

Description: Die Menschheit breitet sich immer mehr über den Planeten aus. Das hat zur Folge, dass urbane Räume Vulkanen immer näherkommen. Manche Städte liegen sehr nah an oder sogar auf einem monogenetischen Feld. Beispiele dafür sind Neapel, Mexico City oder auch Auckland. In solchen Fällen wäre es wichtig zu wissen, wo Lava austreten oder sich ein Vulkankegel bilden könnte. Dr. Eleonora Rivalta vom Deutschen GeoForschungsZentrum (GFZ) beschäftigt sich unter anderem mit solchen Fragestellungen.

Description: Since May 2018, a seismically quiet area offshore the island of Mayotte, Comoros archipelago, has been affected by a complex seismic sequence, including a massive swarm of thousands of earthquakes, long-duration very long period (VLP) signals recorded globally and a large surface deflation recorded by GNSS stations on Mayotte. We systematically analysed regional and global seismological data and local deformation data to provide a detailed picture of a deep, rare magmatic process without any on-site monitoring. We identify and locate ~7000 volcano-tectonic earthquakes (VT) and more than 400 VLPs, and determine the geometry of both faulting and the magma reservoir. Early VTs migrated upward in response to a magmatic dike propagating from Moho depth to the surface, while later events marked the progressive failure of the reservoir’s roof thus triggering its resonance. VLP and deformation analysis suggest that a 10–15 km diameter magmatic body has lost at least 1.3 km3 of magma. This episode represents the deepest monitored drainage of a large reservoir initiating the partial collapse of its roof.

Description: Knowledge of the spatio-temporal changes in the characteristics and distribution of subsurface fluids is key to properly addressing important societal issues, including: sustainable management of energy resources (e.g., hydrocarbons and geothermal energy), management of water resources, and assessment of hazard (e.g., volcanic eruptions). Gravimetry is highly attractive because it can detect changes in subsurface mass, thus providing a window into processes that involve deep fluids. However, high cost and operating features associated with current instrumentation seriously limits the practical field use of this geophysical method. The NEWTON-g project proposes aradical change of paradigm for gravimetry through the development of a field-compatible measuring system (the gravity imager), able to real-time monitor the evolution of the subsurface mass changes. This system includes an array of low-costs microelectromechanical systems-based relative gravimeters, anchored on an absolute quantum gravimeter. It will provide imaging of gravity changes, associated with variations in subsurface fluid properties, with unparalleled spatio-temporal resolution. During the final ∼2 years of NEWTON-g, the gravity imager will be field tested in the summit of Mt. Etna volcano (Italy), where frequent gravity fluctuations, easy access to the active structures and the presence of a multiparameter monitoring system (including traditional gravimeters) ensure an excellent natural laboratory for testing the new tools. Insights from the gravity imager will be used to i) improve our knowledge of the cause-effect relationships between volcanic processes and gravity changes observable at the surface and ii) develop strategies to best incorporate the gravity data into hazards assessments and mitigation plans. A successful implementation of NEWTON-g will open new doors for geophysical exploration.

Description: The dynamics of magma deep in the Earth’s crust are difficult to capture by geophysical monitoring. Since May 2018, a seismically quiet area offshore of Mayotte in the western Indian Ocean has been affected by complex seismic activity, including long-duration, very-long-period signals detected globally. Global Navigation Satellite System stations on Mayotte have also recorded a large surface deflation offshore. Here we analyse regional and global seismic and deformation data to provide a one-year-long detailed picture of a deep, rare magmatic process. We identify about 7,000 volcano-tectonic earthquakes and 407 very-long-period seismic signals. Early earthquakes migrated upward in response to a magmatic dyke propagating from Moho depth to the surface, whereas later events marked the progressive failure of the roof of a magma reservoir, triggering its resonance. An analysis of the very-long-period seismicity and deformation suggests that at least 1.3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth. We demonstrate that such deep offshore magmatic activity can be captured without any on-site monitoring.