A history of deformation within Pietre Cotte rhyolite flow (Vulcano)

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Chemical, Textural and Thermal Analyses of Local Interactions Between Lava Flow and a Tree – Case Study From Pāhoa, Hawai’i

Because many volcanoes are densely vegetated, understanding of the interactions between active lava flows and trees is essential for robust hazard modeling. Tree molds − lava flow features generated when advancing lava engulfs and combusts trees − are widely documented but have, to date, only been described qualitatively. Detailed, quantitative studies of molds can, however, provide insights into the nature of lava-forest interactions. Here, we present a unique characterization of the chemical, textural and thermal interactions between lava and a tree (an Albizia), taking as a case type a basaltic pāhoehoe lava flow that traveled 20 km through Hawaiian rainforest on Kilauea’s East Rift Zone between June and December 2014. The dataset includes chemical analyses of lava (major, trace and volatile species) at the lava-tree contact, quantitative descriptions of lava texture (density, vesicle and crystal populations), and thermal analysis to fingerprint the devolatilization and combustion of wood as well as with cooling and crystallization of lava around the tree. We use these results to construct a three-stage thermal model to describe heat transfer between the lava and the tree, showing how the interaction facilitates combustion of wood and release of its volatile species (CO2 and H2O) into the lava, whilst triggering enhanced cooling and crystallization of lava surrounding the tree. Chemical analyses reveal that the inflating pāhoehoe at the lava-tree contact was strongly CO2-enriched (up to 1200 ppm), and textural data show that lava is denser at the contact. Moreover, lava crystallinity indicates a cooling rate of ∼70°C min–1 at the lava-tree contact, a rate well above the expected cooling rates (30°C min–1) for pāhoehoe more distant (40 m away) from the tree. We conclude that the tree had a local cooling effect on the lava that could potentially influence lava properties at larger scale if tree density, trunk diameter and moisture content are sufficiently hig

The viscosity of pāhoehoe lava: In situ syn-eruptive measurements from Kilauea, Hawaii

Viscosity is one of the most important physical properties controlling lava flow dynamics. Usually, viscosity is measured in the laboratory where key parameters can be controlled but can never reproduce the natural environment and original state of the lava in terms of crystal and bubble contents, dissolved volatiles, and oxygen fugacity. The most promising approach for quantifying the rheology of molten lava in its natural state is therefore to carry out direct field measurements by inserting a viscometer into the lava while it is flowing. Such in-situ syn-eruptive viscosity measurements are notoriously difficult to perform due to the lack of appropriate instrumentation and the difficulty of working on or near an active lava flow. In the field, rotational viscometer measurements are of particular value as they have the potential to measure the properties of the flow interior rather than an integration of the viscosity of the viscoelastic crust + flow interior. To our knowledge only one field rotational viscometer is available, but logistical constraints have meant that it has not been used for 20 years. Here, we describe new viscosity measurements made using the refurbished version of this custom-built rotational viscometer, as performed on active pāhoehoe lobes from the 61G lava flow of Kilauea’s Pu’u ‘Ō‘ō eruption in 2016. We successfully measured a viscosity of ~380 Pa s at strain-rates between 1.6 and 5 s-1 28 and at 1144 °C. Additionally, synchronous lava sampling allowed us to provide detailed textural and chemical characterization of quenched samples. Application of current physico-chemical models based on this characterization (16±4 vol.% crystals; 50±6 vol.% vesicles), gave viscosity estimates that were approximately compatible with the measured values, highlighting the sensitivity of model-based viscosity estimates on the effect of deformable bubbles. Our measurements also agree on the range of viscosities in comparison to previous field experiments on Hawaiian lavas. Conversely, direct comparison with sub-liquidus rheological laboratory measurements on natural lavas was unsuccessful because recreating field conditions (in particular volatile and bubble content) is so far inaccessible in the laboratory. Our work shows the value of field rotational viscometry fully integrated with sample characterization to quantify three-phase lava viscosity. Finally, this work suggests the need for the development of a more versatile instrument capable of recording precise measurements at low torque and low strain rate, and with synchronous temperature measurements

Mesurer la viscosité des laves

International audienceLes coulées de lave constituent l’un des aléas volcaniques les plus fréquents à l’échelle du globe, cependant ce n’est que rarement qu’elles présentent un risque pour les populations (Harris, 2015).Un exemple de coulée de lave meurtrière est fourni par l’éruption du Nyiragongo en République Démocratique du Congo (RDC) en 2002. Deux grandes coulées de lave extrêmement fluides et rapides ont atteint la ville en quelques heures. Plusieurs dizaines de personnes sont décédées (asphyxie par dioxyde de carbone, effondrements de bâtiments à cause de la lave ou des tremblements de terre, explosion de station-service entourée de lave encore chaude), environ 120000 per- sonnes se sont retrouvées sans abri et 15 % de la ville ont été complètement recouverts par la lave.Hormis cet exemple, dans la plupart des cas, les coulées de lave sont assez lentes pour permettre aux populations d’éva- cuer. Cependant, même si les pertes humaines dues aux coulées de lave sont minimes comparées à celles dues aux érup- tions explosives, les coulées de lave détruisent absolument tout sur leur passage (figure 1), ce qui peut avoir des répercus- sions durables sur les économies locales

Mesurer la viscosité des laves

International audienceLes coulées de lave constituent l’un des aléas volcaniques les plus fréquents à l’échelle du globe, cependant ce n’est que rarement qu’elles présentent un risque pour les populations (Harris, 2015).Un exemple de coulée de lave meurtrière est fourni par l’éruption du Nyiragongo en République Démocratique du Congo (RDC) en 2002. Deux grandes coulées de lave extrêmement fluides et rapides ont atteint la ville en quelques heures. Plusieurs dizaines de personnes sont décédées (asphyxie par dioxyde de carbone, effondrements de bâtiments à cause de la lave ou des tremblements de terre, explosion de station-service entourée de lave encore chaude), environ 120000 per- sonnes se sont retrouvées sans abri et 15 % de la ville ont été complètement recouverts par la lave.Hormis cet exemple, dans la plupart des cas, les coulées de lave sont assez lentes pour permettre aux populations d’éva- cuer. Cependant, même si les pertes humaines dues aux coulées de lave sont minimes comparées à celles dues aux érup- tions explosives, les coulées de lave détruisent absolument tout sur leur passage (figure 1), ce qui peut avoir des répercus- sions durables sur les économies locales

Mesurer la viscosité des laves

International audienceLes coulées de lave constituent l’un des aléas volcaniques les plus fréquents à l’échelle du globe, cependant ce n’est que rarement qu’elles présentent un risque pour les populations (Harris, 2015).Un exemple de coulée de lave meurtrière est fourni par l’éruption du Nyiragongo en République Démocratique du Congo (RDC) en 2002. Deux grandes coulées de lave extrêmement fluides et rapides ont atteint la ville en quelques heures. Plusieurs dizaines de personnes sont décédées (asphyxie par dioxyde de carbone, effondrements de bâtiments à cause de la lave ou des tremblements de terre, explosion de station-service entourée de lave encore chaude), environ 120000 per- sonnes se sont retrouvées sans abri et 15 % de la ville ont été complètement recouverts par la lave.Hormis cet exemple, dans la plupart des cas, les coulées de lave sont assez lentes pour permettre aux populations d’éva- cuer. Cependant, même si les pertes humaines dues aux coulées de lave sont minimes comparées à celles dues aux érup- tions explosives, les coulées de lave détruisent absolument tout sur leur passage (figure 1), ce qui peut avoir des répercus- sions durables sur les économies locales

Monitoring Lava Flows

International audienceDuring a volcanic effusive crisis, the active lava flow(s) need(s) to be monitored to best anticipate the possible affected area. A number of measurements needs to be made on site either from ground or from the air and by satellite imagery. These measurements need to be made through established protocols so derivative parameters can be calculated and extracted to contribute to forecasting and reduce possible impacts of lava flows. Measurements and reporting parameters include lava flow setting, morphological description, dimensions (thickness, length, width, underlying slope), temperature (core and surface), and sampling. First order derivative are topographical changes, estimation of emitted lava volume, lava flow velocity (channel and front), cooling rate, petrology and lava flow type characteristics. Second order derivative then involve volumetric discharge rate estimation, heat budget models and rheological constrains. These are essential parameters that are part of the monitoring duties and feed lava flow hazard projection and numerical modelling. In this chapter, we review the measurements that are typically made and the subsequent derivatives that all contribute to monitoring activities during an effusive event

Monitoring Lava Flows

International audienceDuring a volcanic effusive crisis, the active lava flow(s) need(s) to be monitored to best anticipate the possible affected area. A number of measurements needs to be made on site either from ground or from the air and by satellite imagery. These measurements need to be made through established protocols so derivative parameters can be calculated and extracted to contribute to forecasting and reduce possible impacts of lava flows. Measurements and reporting parameters include lava flow setting, morphological description, dimensions (thickness, length, width, underlying slope), temperature (core and surface), and sampling. First order derivative are topographical changes, estimation of emitted lava volume, lava flow velocity (channel and front), cooling rate, petrology and lava flow type characteristics. Second order derivative then involve volumetric discharge rate estimation, heat budget models and rheological constrains. These are essential parameters that are part of the monitoring duties and feed lava flow hazard projection and numerical modelling. In this chapter, we review the measurements that are typically made and the subsequent derivatives that all contribute to monitoring activities during an effusive event

Monitoring Lava Flows

International audienceDuring a volcanic effusive crisis, the active lava flow(s) need(s) to be monitored to best anticipate the possible affected area. A number of measurements needs to be made on site either from ground or from the air and by satellite imagery. These measurements need to be made through established protocols so derivative parameters can be calculated and extracted to contribute to forecasting and reduce possible impacts of lava flows. Measurements and reporting parameters include lava flow setting, morphological description, dimensions (thickness, length, width, underlying slope), temperature (core and surface), and sampling. First order derivative are topographical changes, estimation of emitted lava volume, lava flow velocity (channel and front), cooling rate, petrology and lava flow type characteristics. Second order derivative then involve volumetric discharge rate estimation, heat budget models and rheological constrains. These are essential parameters that are part of the monitoring duties and feed lava flow hazard projection and numerical modelling. In this chapter, we review the measurements that are typically made and the subsequent derivatives that all contribute to monitoring activities during an effusive event

The ∼AD 1250 effusive eruption of El Metate shield volcano (Michoacán, Mexico): magma source, crustal storage, eruptive dynamics, and lava rheology

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