scholarly journals Low-Energy Fragmentation Dynamics at Copahue Volcano (Argentina) as Revealed by an Infrasonic Array and Ash Characteristics

2021 ◽  
Vol 9 ◽  
Author(s):  
Marcia Hantusch ◽  
Giorgio Lacanna ◽  
Maurizio Ripepe ◽  
Veronica Montenegro ◽  
Oscar Valderrama ◽  
...  
Keyword(s):  
Volcanic Ash ◽  
Acoustic Pressure ◽  
Low Energy ◽  
Magma Ascent ◽  
Exit Velocity ◽  
Magma Fragmentation ◽  
Direct Observations ◽  
Infrasonic Waves ◽  
Fragmentation Dynamics ◽  
Explosive Process

Ash-rich eruptions represent a serious risk to the population living nearby as well as at thousands of kilometers from a volcano. Volcanic ash is the result of extensive magma fragmentation during an eruption, and it depends upon a combination of magma properties such as rheology, vesicularity and permeability, gas overpressure and the possible involvement of external fluids during magma ascent. The explosive process generates infrasonic waves which are directly linked to the outflow of the gas-particle mixture in the atmosphere. The higher the overpressure in the magma, the higher should be the exit velocity of the ejected material and the acoustic pressure related to this process. During violent eruptions, fragmentation becomes more efficient and is responsible for the extensive production of ash which is dispersed in the atmosphere. We show that the phase of intense ash emission that occurred during March 2016 at Copahue volcano (Argentina) generated a very low (0.1 Pa) infrasonic amplitude at 13 km, raising a number of questions concerning the links among acoustic pressure, gas overpressure and efficiency of magma fragmentation. Infrasound and direct observations of the eruptive plume indicate that the large quantity of ash erupted at Copahue was ejected with a low exit velocity. Thus, it was associated with eruptive dynamics driven by a low magma overpressure. This is more evident when infrasonic activity at Copahue is compared to the moderate explosive activity of Villarrica (Chile), recorded by the same array, at a distance of 193 km. Our data suggest a process of rigid fragmentation under a low magma overpressure which was nearly completely dissipated during the passage of the erupting mixture through the granular, ash-bearing crater infilling. We conclude that ash released into the atmosphere during low-energy fragmentation dynamics can be difficult to monitor, with direct consequences for the assessment of the related hazard and management of eruptive crises.

Direct Observations of Low-energy Electrons in the Disturbed Ionospheric E-region

Nature ◽  
1964 ◽  
Vol 202 (4934) ◽  
pp. 789-790 ◽  
Author(s):  
W. J. HEIKKILA ◽  
D. L. MATTHEWS
Keyword(s):  
Low Energy ◽  
Direct Observations ◽  
Low Energy Electrons ◽  
E Region

Fragmentation dynamics of condensed phase thymine by low-energy (10–200eV) heavy-ion impact

2005 ◽  
Vol 123 (14) ◽  
pp. 144509 ◽  
Author(s):  
Zongwu Deng ◽  
Marjorie Imhoff ◽  
Michael A. Huels
Keyword(s):  
Condensed Phase ◽  
Heavy Ion ◽  
Low Energy ◽  
Fragmentation Dynamics ◽  
Ion Impact

scholarly journals Shallow crystallization of eruptive magma inferred from volcanic ash microtextures: a case study of the 2018 eruption of Shinmoedake volcano, Japan

2021 ◽  
Vol 83 (5) ◽  
Author(s):  
Keiko Matsumoto ◽  
Nobuo Geshi
Keyword(s):  
Volcanic Ash ◽  
Phase 1 ◽  
Optical Microscope ◽  
Magma Ascent ◽  
Phase 2 ◽  
Eruptive Activity ◽  
Phase 3 ◽  
Vulcanian Explosions ◽  
Lava Effusion

AbstractThe occurrence of groundmass crystals reveals the shallow conduit process of magmas, which affects the behavior of eruptions. Here, we analyzed groundmass microtextures of ash samples from the 2018 eruption of Shinmoedake volcano, Japan, to evaluate the change of magma ascent conditions during the eruption sequence. The eruptive activity changed from ash venting (Phase 1: March 1–6) to lava effusion with continuous ash-laden plumes (Phase 2: March 6–9) and then shifted to Vulcanian explosions (Phase 3: March 10–April 5). Non-juvenile particles were abundant in Phase 1, whereas juvenile particles were dominant in Phases 2 and 3. Vesicular juvenile particles were more abundant in Phase 2 than Phase 3. The lower microlite crystallinity and groundmass SiO2 concentrations of the vesicular particles indicate that they were sourced from magma that ascended rapidly. Abundant nanolites were observed in the black interstitial glass of juvenile particles under an optical microscope, whereas few nanolites were observed in the transparent ones. The presence of nanolites can be explained by the dehydration of silicate melt, as well as cooling and oxidation between fragmentation and quenching. Temporal changes in the ash componentry show that the eruption activity started from the erosion of the pre-existing vent plug (Phase 1), shifted to the simultaneous eruption of bubble-bearing and outgassed magmas (Phase 2), and concluded with explosions of the stagnant lava (Phase 3), thereby demonstrating the sequence of vent opening and extrusion and stagnation of magma. Therefore, ash microtextures are valuable for monitoring the shallow conduit process of eruptive magma.

A Multicoincidence Study of Fragmentation Dynamics in Collision of γ-Aminobutyric Acid with Low-Energy Ions

2012 ◽  
Vol 18 (30) ◽  
pp. 9321-9332 ◽  
Author(s):  
Michael Capron ◽  
Sergio Díaz-Tendero ◽  
Sylvain Maclot ◽  
Alicja Domaracka ◽  
Elie Lattouf ◽  
...  
Keyword(s):  
Low Energy ◽  
Aminobutyric Acid ◽  
Fragmentation Dynamics ◽  
Low Energy Ions

Morpho-textural and dynamic analysis of ash particles and ash aggregates at Sakurajima volcano (Japan)

2020 ◽  
Author(s):  
Pietro Gabellini ◽  
Costanza Bonadonna ◽  
Raffaello Cioni ◽  
Marco Pistolesi ◽  
Nobuo Geshi ◽  
...  
Keyword(s):  
Grain Size ◽  
High Speed ◽  
Volcanic Ash ◽  
Numerical Models ◽  
Fragmentation Process ◽  
Large Set ◽  
Sakurajima Volcano ◽  
High Speed Video ◽  
Magma Fragmentation ◽  
Ash Aggregates

<p><span>Morphological, textural and granulometric studies of volcanic ash particle provides important insights into the mechanisms of fragmentation, transport and deposition in the context of low-to-mid intensity activity, and particularly during those eruptions showing high-transients in the style of activity. A comprehensive study of volcanic ash from Vulcanian activity of variable intensity at Sakurajima volcano (Japan) is here presented together with a detailed analysis of ash aggregates collected and filmed during the same eruptive sequences. Bulk tephra deposits from different events (July-August 2013, October 2014 and November 2019) and high-speed video of falling ash aggregates were collected directly during the fallout. Tephra samples, resulting from the different phases of activity, were analyzed using an optical particle analyzer which allowed to characterized the grain size distribution and to quantify the shape of a large set of particles. A set of objective parameters were used to constrain the shape of ash grains. This helped to better characterize different phases of activity also in the light of the magma fragmentation process and to evaluate the role played by the fragmentation process in controlling the eruption dynamics. SEM analyses of representative ash grains allowed distinguishing four principal types of ash fragments basing on morphological, surface and groundmass features: Blocky Irregular (BI), Blocky Regular (BR), Vesicular (V). A comprehensive textural analysis of grains belonging to either the different classes and phases of activity was provided in order to better resolve the complex relationships between the processes occurring before and during magma fragmentation and secondary processes affecting ash characteristics, like the intra-crateric recycling of ash. This helped also to shed light on the different processes of ash production and link them with the resulting dynamics of activity in the context of unsteady eruptions. On the other hand, the analysis of the high-speed video depicting ash aggregates, and aggregates collected during the same eruptive periods revealed important information about the influence of ash aggregation in controlling the depositional dynamics of Vulcanian eruptions. Three main types of ash aggregates were recognized to occur into all the Sakurajima samples: Ash Clusters, Coated Particles, Cored Clusters. Using image analysis techniques of SEM images, collected aggregates were characterized in terms of dimension, grain size of the aggregating ash, and shape features of the aggregated ash, pointing out important differences between the different types. Analysis of high-resolution, High-speed Camera video recordings, allowed finally to collect an important set of measurements of terminal velocity, bulk density, and size of a large number of observed falling aggregates. The resulting data reveal the strong influence of aggregation processes in controlling ash deposition processes at Sakurajima, and also represent a valuable dataset useful for validation and calibration of numerical models.</span></p>

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