scholarly journals The Entrainment Rate of Non‐Boussinesq Hazardous Geophysical Gas‐Particle Flows: An Experimental Model With Application to Pyroclastic Density Currents

2019 ◽  
Vol 46 (22) ◽  
pp. 12851-12861 ◽  
Author(s):  
P. Dellino ◽  
F. Dioguardi ◽  
D. M. Doronzo ◽  
D. Mele
Keyword(s):  
Experimental Model ◽  
Entrainment Rate ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Particle Flows

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 constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows

2021 ◽  
Author(s):  
Adrian Hornby ◽  
Ulrich Kueppers ◽  
Benedikt Maurer ◽  
Carina Poetsch ◽  
Donald Dingwell
Keyword(s):  
Experimental Approach ◽  
Direct Evidence ◽  
General Description ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Shape Factors ◽  
Material Density ◽  
Bed Height ◽  
Rotary Drum ◽  
Basal Flow

<p>Pyroclastic density currents (PDCs) present perhaps the greatest proximal primary hazard of volcanic activity and produce abundant fine ash that can present a range of health, environment and infrastructure hazards. However, direct, fully quantitative observation of ash production in PDCs is lacking, and little direct evidence exists to constrain the parameters controlling ash generation in PDCs. Here, we use an experimental approach to investigate the effects of starting mass, material density and ash removal on the efficiency of ash generation and concurrent clast rounding in the dense basal flow of PDCs. We employ a rotary drum to tumble pumice and scoria lapilli clasts over multiple transport “distance” steps (from 0.2 to 6 km). We observe increased ash generation rates with the periodic removal of ash during the experiments and with increasing starting mass. By scaling to the bed height and clast diameter we obtain a general description for ash production in all experiments as a function of flow distance, bed height and average clast diameter. We confirm that changes in lapilli shape factors correlate with the ash fraction generated and that the grain size of ash produced decreases with distance. Finally, we estimate shear rate in our experiments and calculate the inertial number, which describes the ratio between clast-scale and flow-scale rearrangement during flow. We show that, under certain conditions, fractional ash production can be calculated accurately for any starting mass solely as a function of the inertial number and the flow distance. This work sheds light on some of the first systematic and generalizable experimental parameterizations of ash production and associated clast evolution in PDCs and should advance our ability to understand flow mobility and associated hazards.</p>

The numerical reconstruction of three past eruptions at Gede volcano (Indonesia)

2021 ◽  
Author(s):  
Eleanor Tennant ◽  
Susanna Jenkins ◽  
Annie Winson ◽  
Christina Widiwijayanti ◽  
Hendra Gunawan ◽  
...  
Keyword(s):  
Epistemic Uncertainty ◽  
Source Parameters ◽  
Frictional Resistance ◽  
Collapse Mechanism ◽  
Eruption Dynamics ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Basal Friction ◽  
Column Collapse ◽  
Hazard And Risk

<p>Understanding past eruption dynamics at a volcano is crucial for forecasting the range of possible future eruptions and their associated hazards and risk. In this work we reconstructed pyroclastic density currents and tephra fall from three eruptions at Gede volcano, Indonesia with the aim of gaining further insight into past eruptions and identifying suitable eruption source parameters for future hazard and risk assessment. Gede has the largest number of people living within 100 km of any volcano worldwide, and has exhibited recent unrest activity, yet little is known about its eruption history. For pyroclastic density currents, we used Titan2D to reconstruct geological deposits dated at 1200 and c. 1000 years BP. An objective and quantitative multi-criteria method was developed to evaluate the fit of over 300 pyroclastic density current (PDC) model simulations to field observations. We found that the 1200 years BP geological deposits could be reproduced with either a dome collapse or column collapse as the generation mechanism although a relatively low basal friction of 6 degrees would suggest that the PDCs were markedly mobile. Lower basal frictions may reflect the occurrence of previous PDCs that smoothed the path, reducing frictional resistance and enabling greater runout for the reconstructed unit. For the 1,000 years BP PDC, a column collapse mechanism and higher basal friction was required to fit the geological deposits. In agreement with previous studies, we found that Titan2D simulations were most sensitive to the basal friction; however, we also found that the internal friction – often fixed and considered of low influence on outputs - can have a moderate effect on the simulated average deposit thickness. We used Tephra2 to reconstruct historic observations of tephra dispersed to Jakarta and other towns during the last known magmatic eruption of Gede in 1948. In the absence of observable field deposits, or detailed information from the published literature, we stochastically sampled eruption source parameters from wide ranges informed by analogous volcanic systems. Our modelling suggests that the deposition of tephra in Jakarta during the November 1948 eruption was a very low probability event, with approximately a 0.03 % chance of occurrence. Through this work, we exemplify the reconstruction of past eruptions when faced with epistemic uncertainty, and improve our understanding of past eruption dynamics at Gede volcano, providing a crucial step towards the reduction of risk to nearby populations through volcanic hazard assessment.</p>

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