E. C. P. Breard

Synthesizing large-scale pyroclastic flows: Experimental design, scaling, and first results from PELE

Pyroclastic flow eruption large-scale experiment (PELE) is a large-scale facility for experimental studies of pyroclastic density currents (PDCs). It is used to generate high-energy currents involving 500–6500 m3 natural volcanic material and air that achieve velocities of 7–30 m s−1, flow thicknesses of 2–4.5 m, and runouts of >35 m. The experimental PDCs are synthesized by a controlled “eruption column collapse” of ash-lapilli suspensions onto an instrumented channel. The first set of experiments are documented here and used to elucidate the main flow regimes that influence PDC dynamic structure. Four phases are identified: (1) mixture acceleration during eruption column collapse, (2) column-slope impact, (3) PDC generation, and (4) ash cloud diffusion. The currents produced are fully turbulent flows and scale well to natural PDCs including small to large scales of turbulent transport. PELE is capable of generating short, pulsed, and sustained currents over periods of several tens of seconds, and dilute surge-like PDCs through to highly concentrated pyroclastic flow-like currents. The surge-like variants develop a basal <0.05 m thick regime of saltating/rolling particles and shifting sand waves, capped by a 2.5–4.5 m thick, turbulent suspension that grades upward to lower particle concentrations. Resulting deposits include stratified dunes, wavy and planar laminated beds, and thin ash cloud fall layers. Concentrated currents segregate into a dense basal underflow of <0.6 m thickness that remains aerated. This is capped by an upper ash cloud surge (1.5–3 m thick) with 100 to 10−4 vol % particles. Their deposits include stratified, massive, normally and reversely graded beds, lobate fronts, and laterally extensive veneer facies beyond channel margins.

Jacques-Marie Bardintzeff: Tout savoir sur les volcans du monde, séismes et tsunamis

Volcanoes are spectacular manifestations of our dynamic planet and fascinate us with their beauty and enigmatic behaviour. Nonetheless, volcanoes potentially threaten over 500 million people living close enough to be affected by medium-scale eruptions (Cashman and Sparks 2013). Large-scale eruptions, from what the media commonly call “super-volcanoes” (e.g. c.73 ka Toba eruption, Rose and Chesner 1987; Rampino and Self 1992), have in the past affected the Earth’s climate and may have resulted in the decline of humans and other species across the globe (Forster 2004; Williams et al. 2009). Nearly everyone in the world has encountered active or dormant volcanoes, therefore bridging the knowledge gap between volcanologists and the population is a priority. This has been the aim of Jacques-Marie Bardintzeff for the past two decades. “Tout savoir sur les volcans du monde, séismes et tsunamis, 2 édition” joins a long list of popular books written in French by the author. While there are no clear specifications about the age of the target audience for this book, it would surely be welcome by 10–18 year olds and could awaken their curiosity towards volcanoes. The text is written in simple and transparent language, helped by the presence of a glossary at the end of the book defining the scientific words, and further illustrated by multiple pictures and sketches. J.-M. Bardintzeff gives a brief overview over six parts (composed of 27 chapters of few pages only) of the volcanoes, which he brings to life with passionate, expressive language, vividly accompanied by pictures of the volcanic phenomenon that the author has experienced across the world. I below summarize the chapters’ contents and add few comments where needed. Chapter 1 discusses the relationship between volcanoes and humans through historical times and their importance in various cultures. Chapters 2 and 3 describe the origin of volcanoes on Earth, and their respective locations. The book is not confined to volcanoes on Earth; extra-terrestrial volcanoes are also mentioned. These chapters include a helpful map of active volcanoes (pp. 16–17); however, the map does not include all volcanoes, if by active, the author means volcanoes that erupted historically or in the past 10,000 years (Rymer 2015). While c. 80 volcanoes are represented on the map, over 1500 volcanoes solely on land are known as active following the classical description. If the author meant by “active”, volcanoes that Editorial responsibility: K. Németh