density currents
Recently Published Documents


TOTAL DOCUMENTS

601
(FIVE YEARS 132)

H-INDEX

45
(FIVE YEARS 5)

2022 ◽  
Vol 148 (3) ◽  
Author(s):  
Hassan Ismail ◽  
Jasim Imran
Keyword(s):  

2021 ◽  
pp. SP520-2021-144
Author(s):  
Marie-Noëlle Guilbaud ◽  
Corentin Chédeville ◽  
Ángel Nahir Molina-Guadarrama ◽  
Julio Cesar Pineda-Serrano ◽  
Claus Siebe

AbstractThe eruption of the ∼10 km3 rhyolitic Las Derrumbadas twin domes about 2000 yrs ago has generated a wide range of volcano-sedimentary deposits in the Serdán-Oriental lacustrine basin, Trans-Mexican Volcanic Belt. Some of these deposits have been quarried, creating excellent exposures. In this paper we describe the domes and related products and interpret their mode of formation, reconstructing the main phases of the eruption as well as syn-and-post eruptive erosional processes. After an initial phreatomagmatic phase that built a tuff ring, the domes grew as an upheaved plug lifting a thick sedimentary pile from the basin floor. During uplift, the domes collapsed repeatedly to form a first-generation of hetero-lithologic hummocky debris avalanche deposits. Subsequent dome growth produced a thick talus and pyroclastic density currents. Later, the hydrothermally-altered over-steepened dome peaks fell to generate 2nd generation, mono-lithologic avalanches. Subsequently, small domes grew in the collapse scars. From the end of the main eruptive episode onwards, heavy rains remobilized parts of the dome carapaces and talus, depositing lahar aprons. Las Derrumbadas domes are still an important source of sediments in the basin, and ongoing mass-wasting processes are associated with hazards that should be assessed, given their potential impact on nearby populations.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5752296


Author(s):  
Magfira Syarifuddin ◽  
Susanna Jenkins ◽  
Benoit Taisne ◽  
Satoru Oishi ◽  
Ahmad Basuki ◽  
...  

Climate ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 170
Author(s):  
Michael L. Kaplan ◽  
Curtis N. James ◽  
Jan Ising ◽  
Mark R. Sinclair ◽  
Yuh-Lang Lin ◽  
...  

The deadly shift of the Yarnell Hill, Arizona wildfire was associated with an environment exhibiting gusty wind patterns in response to organized convectively driven circulations. The observed synoptic (>2500 km) through meso-β (approximately 100 km) scale precursor environment that organized a mid-upper tropospheric cross-mountain mesoscale jet streak circulation and upslope thermally direct flow was examined. Numerical simulations and observations indicated that both circulations played a key role in focusing the upper-level divergence, ascent, downdraft potential, vertical wind shear favoring mobile convective gust fronts, and a microburst. This sequence was initiated at the synoptic scale by a cyclonic Rossby Wave Break (RWB) 72 h prior, followed by an anticyclonic RWB. These RWBs combined to produce a mid-continent baroclinic trough with two short waves ushering in cooler air with the amplifying polar jet. Cool air advection with the second trough and surface heating across the Intermountain West (IW) combined to increase the mesoscale pressure gradient, forcing a mid-upper tropospheric subsynoptic jet around the periphery of the upstream ridge over Southern Utah and Northern New Mexico. Convection was triggered by an unbalanced secondary jetlet circulation within the subsynoptic jet in association with a low-level upslope flow accompanying a mountain plains solenoidal circulation above the Mogollon Rim (MR) and downstream mountains.


2021 ◽  
Author(s):  
◽  
Alexa R Van Eaton

<p>This work investigates the dynamics of large-scale, ‘wet’ volcanic eruption clouds generated by the interaction of silicic magma with external water. The primary case study draws from a detailed record of non-welded pyroclastic deposits from the ~25.4 ka Oruanui eruption of Taupo volcano, New Zealand, one of the largest phreatomagmatic eruptions documented worldwide. This research uses a three-pronged approach, integrating results from (i) field observations and textural data, (ii) mesoscale numerical modeling of volcanic plumes, and (iii) analogue laboratory experiments of volcanic ash aggregation. This interdisciplinary approach provides a new understanding of dynamic and microphysical interactions between collapsing and buoyant columns, and how this behavior controls the large-and small-scale nature of phreatoplinian eruption clouds. Stratigraphic field studies examine the styles of dispersal and emplacement of deposits from several phases of the Oruanui eruption (primarily phases 2, 3, 5, 6, 7 and 8). Detailed stratigraphic observations and laser diffraction particle size analysis of ash aggregates in these deposits clarify the evolution of aggregation mechanisms with time through the relevant eruption phase, and with distance from vent. Deposits of the wettest phase (3) show the key role of turbulent lofting induced by pyroclastic density currents in forming aggregates, particularly those with ultrafine ash rims (30-40 vol.% finer than 10 μm) which are uniquely formed in the ultrafine ash-dominated clouds above the currents. Drier deposits of phases 2 and 5, which also saw lower proportions of material emplaced by pyroclastic density currents, contain fewer aggregates that are related to low water contents in the medial to distal plume. Discovery and documentation of high concentrations of diatom flora in the Oruanui deposits indicates efficient fragmentation and incorporation of paleo-lake Taupo sediments during the eruption. This highlights the potential for incidental contamination of volcanic deposits with broader implications for correlation of distal tephras and possible contamination of paleoenvironmental records due to incorporation of diachronous populations of volcanically-dispersed diatoms. The impact of extensive surface water interaction on large-scale volcanic eruptions (>108 kg s-1 magma) is examined by employing the first 2-D large-eddy simulations of ‘wet’ volcanic plumes that incorporate the effects of microphysics. The cloud-resolving numerical model ATHAM was initialized with field-derived characteristics of the Oruanui case study. Surface water contents were varied from 0-40 wt.% for eruptions with equivalent magma eruption rates of c. 1.3 x108 and 1.1 x109 kg s-1. Results confirm that increased surface water has a pronounced impact on column stability, leading to unstable column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents (PDCs). Contrary to the suggestion of previous studies, however, abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds, owing to vigorous microphysics-assisted lofting of PDCs. Key processes influencing the aggregation of volcanic ash and hydrometeors (airborne water phases) are examined with a simple and reproducible experimental method employing vibratory pan agglomeration. Aggregation processes in the presence of hail and graupel, liquid water (<30 wt.%), and mixed water phases are investigated at temperatures from 18 to -20 °C. Observations from impregnated thin sections, SEM images and x-ray computed microtomography of these experimental aggregates closely match natural examples from phreatomagmatic phases of the ~25.4 ka Oruanui and Eyjafjallajökull (May 2010) eruptions. These experiments demonstrate that the formation of concentric, ultrafine rims comprising the outer layers of rim-type accretionary lapilli requires recycled exposure of moist, preexisting pellets to regions of volcanic clouds that are relatively dry and dominated by ultrafine (<31 μm) ash. This work presents the first experimentally-derived aggregation coefficients that account for changing liquid water contents and sub-zero temperatures, and indicates that dry conditions (<10 wt.% liquid) promote the strongly size-selective collection of sub-31 μm particles into aggregates (given by aggregation coefficients >1). These quantitative relationships may be used to predict the timescales and characteristics of aggregation, such as aggregate size spectra, densities and constituent particle size characteristics, when the initial size distribution and hydrometeor content of a volcanic cloud are known. The integration of numerical modeling, laboratory experimentation and field data lead to several key conclusions. (1) The importance of the microphysics of ash-water interactions in governing the eruption cloud structure, boosting the dispersal power of the cloud and controlling aggregate formation in response to differing water contents and eruption rates. (2) Recognition of the contrasting roles of differential aggregation versus cloud grain size in controlling the formation and nature of aggregate particles, notably those with characteristic ultrafine outer rims. (3) The importance of pyroclastic density currents as triggers for convection and aggregation processes in the eruption cloud.</p>


2021 ◽  
Author(s):  
◽  
Alexa R Van Eaton

<p>This work investigates the dynamics of large-scale, ‘wet’ volcanic eruption clouds generated by the interaction of silicic magma with external water. The primary case study draws from a detailed record of non-welded pyroclastic deposits from the ~25.4 ka Oruanui eruption of Taupo volcano, New Zealand, one of the largest phreatomagmatic eruptions documented worldwide. This research uses a three-pronged approach, integrating results from (i) field observations and textural data, (ii) mesoscale numerical modeling of volcanic plumes, and (iii) analogue laboratory experiments of volcanic ash aggregation. This interdisciplinary approach provides a new understanding of dynamic and microphysical interactions between collapsing and buoyant columns, and how this behavior controls the large-and small-scale nature of phreatoplinian eruption clouds. Stratigraphic field studies examine the styles of dispersal and emplacement of deposits from several phases of the Oruanui eruption (primarily phases 2, 3, 5, 6, 7 and 8). Detailed stratigraphic observations and laser diffraction particle size analysis of ash aggregates in these deposits clarify the evolution of aggregation mechanisms with time through the relevant eruption phase, and with distance from vent. Deposits of the wettest phase (3) show the key role of turbulent lofting induced by pyroclastic density currents in forming aggregates, particularly those with ultrafine ash rims (30-40 vol.% finer than 10 μm) which are uniquely formed in the ultrafine ash-dominated clouds above the currents. Drier deposits of phases 2 and 5, which also saw lower proportions of material emplaced by pyroclastic density currents, contain fewer aggregates that are related to low water contents in the medial to distal plume. Discovery and documentation of high concentrations of diatom flora in the Oruanui deposits indicates efficient fragmentation and incorporation of paleo-lake Taupo sediments during the eruption. This highlights the potential for incidental contamination of volcanic deposits with broader implications for correlation of distal tephras and possible contamination of paleoenvironmental records due to incorporation of diachronous populations of volcanically-dispersed diatoms. The impact of extensive surface water interaction on large-scale volcanic eruptions (>108 kg s-1 magma) is examined by employing the first 2-D large-eddy simulations of ‘wet’ volcanic plumes that incorporate the effects of microphysics. The cloud-resolving numerical model ATHAM was initialized with field-derived characteristics of the Oruanui case study. Surface water contents were varied from 0-40 wt.% for eruptions with equivalent magma eruption rates of c. 1.3 x108 and 1.1 x109 kg s-1. Results confirm that increased surface water has a pronounced impact on column stability, leading to unstable column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents (PDCs). Contrary to the suggestion of previous studies, however, abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds, owing to vigorous microphysics-assisted lofting of PDCs. Key processes influencing the aggregation of volcanic ash and hydrometeors (airborne water phases) are examined with a simple and reproducible experimental method employing vibratory pan agglomeration. Aggregation processes in the presence of hail and graupel, liquid water (<30 wt.%), and mixed water phases are investigated at temperatures from 18 to -20 °C. Observations from impregnated thin sections, SEM images and x-ray computed microtomography of these experimental aggregates closely match natural examples from phreatomagmatic phases of the ~25.4 ka Oruanui and Eyjafjallajökull (May 2010) eruptions. These experiments demonstrate that the formation of concentric, ultrafine rims comprising the outer layers of rim-type accretionary lapilli requires recycled exposure of moist, preexisting pellets to regions of volcanic clouds that are relatively dry and dominated by ultrafine (<31 μm) ash. This work presents the first experimentally-derived aggregation coefficients that account for changing liquid water contents and sub-zero temperatures, and indicates that dry conditions (<10 wt.% liquid) promote the strongly size-selective collection of sub-31 μm particles into aggregates (given by aggregation coefficients >1). These quantitative relationships may be used to predict the timescales and characteristics of aggregation, such as aggregate size spectra, densities and constituent particle size characteristics, when the initial size distribution and hydrometeor content of a volcanic cloud are known. The integration of numerical modeling, laboratory experimentation and field data lead to several key conclusions. (1) The importance of the microphysics of ash-water interactions in governing the eruption cloud structure, boosting the dispersal power of the cloud and controlling aggregate formation in response to differing water contents and eruption rates. (2) Recognition of the contrasting roles of differential aggregation versus cloud grain size in controlling the formation and nature of aggregate particles, notably those with characteristic ultrafine outer rims. (3) The importance of pyroclastic density currents as triggers for convection and aggregation processes in the eruption cloud.</p>


Sign in / Sign up

Export Citation Format

Share Document