scholarly journals Inverting Sediment Bedforms for Exploring the Hazard of Volcanic Density Currents Directly in the Field

2021 ◽  
Author(s):  
Pierfrancesco Dellino ◽  
Fabio Dioguardi ◽  
Roberto Sulpizio ◽  
Daniela Mele
Keyword(s):  
Phase Diagram ◽  
Grain Size ◽  
High Speed ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Explosive Volcanism ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Particle Flows ◽  
First Time

Abstract Pyroclastic density currents are ground hugging gas-particle flows moving at high speed down the volcano slope. They are among the most hazardous events of explosive volcanism, causing devastation and deaths1,2. Because of the hostile nature they cannot be analyzed directly and most of their fluid dynamic behavior is reconstructed by the deposits left in the geological record, which frequently show peculiar structures such as bedforms of the types of ripples and dunes3,4. In this paper, we simplify a set of equations that link flow behavior to particle motion and deposition. This allows, for the first time, the build up of a phase diagram by which the hazard of dilute pyroclastic density currents can be explored easily and quickly by inverting bedforms wavelength and grain size.

scholarly journals The impact of pyroclastic density currents duration on humans: the case of the AD 79 eruption of Vesuvius

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Pierfrancesco Dellino ◽  
Fabio Dioguardi ◽  
Roberto Isaia ◽  
Roberto Sulpizio ◽  
Daniela Mele
Keyword(s):  
Thermal Effects ◽  
High Speed ◽  
Dynamic Pressure ◽  
Eruption Column ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Flow Duration ◽  
Particle Flows ◽  
The Impact ◽  
A Current

AbstractPyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome. They move away from the volcano at high speed, causing devastation. The impact is generally associated with flow dynamic pressure and temperature. Little emphasis has yet been given to flow duration, although it is emerging that the survival of people engulfed in a current strongly depends on the exposure time. The AD 79 event of Somma-Vesuvius is used here to demonstrate the impact of pyroclastic density currents on humans during an historical eruption. At Herculaneum, at the foot of the volcano, the temperature and strength of the flow were so high that survival was impossible. At Pompeii, in the distal area, we use a new model indicating that the current had low strength and low temperature, which is confirmed by the absence of signs of trauma on corpses. Under such conditions, survival should have been possible if the current lasted a few minutes or less. Instead, our calculations demonstrate a flow duration of 17 min, long enough to make lethal the breathing of ash suspended in the current. We conclude that in distal areas where the mechanical and thermal effects of a pyroclastic density currents are diminished, flow duration is the key for survival.

Experimental determination of fragmentation efficiency for Plinian and Pelean eruptions of Mt. Pelée, Martinique

2021 ◽  
Author(s):  
Mila Huebsch ◽  
Ulrich Kueppers ◽  
Guillaume Carazzo ◽  
Anne-Marie Lejeune ◽  
Audrey Michaud-Dubuy ◽  
...  
Keyword(s):  
Grain Size ◽  
Fractal Dimension ◽  
Open Porosity ◽  
High Speed ◽  
Model Development ◽  
Active Volcano ◽  
Petrophysical Properties ◽  
Density Currents ◽  
Fragmentation Efficiency ◽  
Plinian Eruptions

<p>Mt. Pelée is a historically active volcano, situated on the island of Martinique (Lesser Antilles), that has shown a variety of explosive styles in the recent past, ranging from dome-forming (Pelean) to open-vent (Plinian) eruptions.  The 1902-1905 eruption is infamous for the pyroclastic density currents (PDCs) that destroyed the towns of St. Pierre and Morne Rouge, killing 30 000 residents.  Since the last eruption (dome-forming) in 1929-1932, Mt. Pelée was quiet and considered dormant until recently.  In late 2020, the local Volcanological Observatory (OVSM) raised the alert level following a noticeable increase in seismicity, bringing into effect a reinforcement of monitoring resources.  As St. Pierre is long since re-established, along with several other towns along the volcano’s flanks, it is of utmost importance to understand the possible range of eruptive activity to improve the preparedness strategies of local communities.</p><p>The precise controls on eruption dynamics vary across volcanic systems and cannot be constrained via direct observation. However, crucial inferences can be made based on petrophysical properties and mechanical behaviours of erupted materials.  For this study, we collected samples from PDC deposits of Mt. Pelée, from the two historic Pelean (1902-1905, and 1929-1932) and three pre-Columbian Plinian eruptions (1300 CE P1, 280 CE P2, and 79 CE P3). We measured petrophysical properties (density, porosity, permeability) of cylindrical samples drilled from bomb-sized clasts and investigated their fragmentation behaviour via grain size and high-speed video analysis. These results are used in comparison with field data of grain-size distribution (GSD) of individual outcrops and calculated total GSD data.  We investigated the effects of transport-related sorting or fining.</p><p>The “Pelean” samples are found to be denser (32-47% open porosity) than the pumiceous “Plinian” samples (55-66% open porosity).  Moreover, these two classes are distinctly different in their crystallinity as samples underwent different ascent conditions.  In our experiments, distinct fragmentation behaviour and resulting GSDs are observed for samples from each eruption style, regardless of experimental pressure conditions (5-20 MPa). Our results show the paramount importance of open porosity on fragmentation efficiency in pumiceous samples, alongside a strong influence of crystallinity.  The fractal dimension of fragmentation calculated from weight fractions, independent of grain shape, shows clear differences in fragmentation efficiency as a function of sample properties and experimental starting conditions.</p><p>Our results suggest that (i) the variability in porosity and permeability is too low to cause the increased explosivity exhibited during the 1902 eruption compared to the 1929 event, (ii) open porosity has a major control on fragmentation efficiency in pumiceous samples, (iii) fragmentation efficiency can be effectively evaluated by calculating the fractal dimension of the cumulative weight fractions of experimental products.</p><p>The influence of crystallinity and pore textures on fragmentation efficiency must be further investigated to aid hazard model development for future eruptions of Mt. Pelée. Future work will constrain these textural parameters of naturally and experimentally fragmented materials from Mt. Pelée, to further elucidate the controls on eruptive dynamics at this hazardous volcano.</p>

Fluid dynamic analog experiments on “Pele’s hair” using a handmade cotton candy machine

2020 ◽  
Author(s):  
Ichiro Kumagai ◽  
Miyuki Yamada
Keyword(s):  
Formation Process ◽  
High Speed ◽  
Heating Temperature ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Glass Fibers ◽  
Volcanic Glass ◽  
Rotating Disk ◽  
Rotating Speed ◽  
Cotton Candy

<p>On the south flank of Kilauea volcano in Hawaii Island, we will find glass fibers called “Pele’s hair” in the volcanic products of lava fountains and explosions. It is named after Pele, who is the Hawaiian goddess of volcanos. “Pele’s hairs” are highly stretched volcanic glass products, which are formed by breakup, stretching, and cooling of molten magma during their eruption. The texture of the glass fibers (thickness and length of fibers) depend on many parameters such as rheological properties of the volcanic glass, cooling rate, ejection speed, wind velocity, and so on. In order to consider the formation process of “Pele’s hair” in classroom experiments, we developed a handmade cotton candy maker. We used a commercial stirrer which could control the rotating speed. At the edge of the stirrer, we attached a rotating dish, which was made of thin steel and had small outlets along its periphery. To make fibers of sugars (threads of cotton candy), crystal sugar (“Za-ra-me” in Japanese, coarse sugar) was added to the dish and rotated at a constant speed. The melted sugar was formed after heating the rotating disk and ejected through the outlets. We measured the temperature of the melted sugar by a commercial radiation thermometer and the flow behavior of the melted sugar jet was captured by a high-speed video camera, which helped us to understand the formation process. By controlling the rotating speed, heating temperature and diameter of the outlets, we have succeeded in producing a variety of analog “Pele’s hair” and Pele’s tear”. We carefully examined the texture of the analogue Pele’s products and discussed the role of these controlling parameters on their formation process. In this presentation, we will also discuss the similarity of the texture of Pele’s hairs, which were sampled from volcanic products in Hawaii Islands, with the analog Pele’s hairs of cotton candy using a commercial digital microscope.</p>

Isolation and HPLC Determination of the Chemical Components of Gentianella acuta (Michx.) Hulten

2018 ◽  
Vol 15 (1) ◽  
pp. 21-33
Author(s):  
Ying Wei ◽  
Yongqiao Liu ◽  
Yifan Hele ◽  
Weiwei Sun ◽  
Yang Wang ◽  
...  
Keyword(s):  
Medicinal Plant ◽  
High Speed ◽  
Chemical Constituents ◽  
Folk Medicine ◽  
Gradient Elution ◽  
Chemical Components ◽  
Isolation And Characterization ◽  
Major Chemical ◽  
Main Components ◽  
First Time

Background: Gentianella acuta (Michx.) Hulten is an important type of medicinal plant found in several Chinese provinces. It has been widely used in folk medicine to treat various illnesses. However, there is not enough detailed information about the chemical constituents of this plant or methods for their content determination. Objective: The focus of this work is the isolation and characterization of the major chemical constituents of Gentianella acuta, and developing an analytical method for their determination. Methods: The components of Gentianella acuta were isolated using (1) ethanol extraction and adsorption on macroporous resin. (2) and ethyl acetate extraction and high speed countercurrent chromatography. A HPLC-DAD method was developed using a C18 column and water-acetonitrile as the mobile phase. Based on compound polarities, both isocratic and gradient elution methods were developed. Results: A total of 29 compounds were isolated from this plant, of which 17 compounds were isolated from this genus for the first time. The main components in this plant were found to be xanthones. The HPLC-DAD method was developed and validated for their determination, and found to show good sensitivity and reliability. Conclusion: The results of this work add to the limited body of work available on this important medicinal plant. The findings will be useful for further investigation and development of Gentianella acuta for its valuable medicinal properties.

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