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

International audienc

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

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

International audienc

The effects of digital elevation model resolution on the PyFLOWGO thermorheological lava flow model

co-auteur étrangerInternational audienceTopography is a fundamental factor influencing the emplacement of lava flows. We assess the impact of topographic resolution on the thermorheological PyFLOWGO model, specifically with digital elevation model (DEM) resolutions commonly available for Earth and other planetary bodies where flow modeling is relevant. We examined PyFLOWGO output parameters (e.g., channel length, core temperature, and flow velocity) to assess model sensitivity to topography in order to document model uncertainties and optimize future application. This study uses rheologic and topographic data from the Tolbachik, Russia 2012–2013 eruption as model constraints. Using moderate to lower resolution topographic data overestimates the channelized flow length by up to 35% due to differences in the distribution of slopes topographic variability at different resolutions and resulting effects on the modeled lava velocity down channel. Determining the impact of topography on thermorheological lava flow models such as PyFLOWGO is important to correctly interpret the results for channelized flows

PyFLOWGO: An open-source platform for simulation of channelized lava thermo-rheological properties

Co-auteur étrangerInternational audienceLava flow advance can be modeled through tracking the evolution of the thermo-rheological properties of acontrol volume of lava as it cools and crystallizes. An example of such a model was conceived by Harris andRowland (2001) who developed a 1-D model, FLOWGO, in which the velocity of a control volume flowing down achannel depends on rheological properties computed following the thermal path estimated via a heat balance boxmodel. We provide here an updated version of FLOWGO written in Python that is an open-source, modern andflexible language. Our software, named PyFLOWGO, allows selection of heat fluxes and rheological models of theuser's choice to simulate the thermo-rheological evolution of the lava control volume. We describe its architecturewhich offers more flexibility while reducing the risk of making error when changing models in comparison to theprevious FLOWGO version. Three cases are tested using actual data from channel-fed lava flow systems and resultsare discussed in terms of model validation and convergence. PyFLOWGO is open-source and packaged in a Pythonlibrary to be imported and reused in any Python program (https://github.com/pyflowgo/pyflowgo)

Viscous flow behavior of tholeiitic and alkaline Fe-rich martian basalts

International audienceThe chemical compositions of martian basalts are enriched in iron with respect to terrestrial basalts. Their rheology is poorly known and liquids of this chemical composition have not been experimentally investigated. Here, we determine the viscosity of five synthetic silicate liquids having compositions representative of the diversity of martian volcanic rocks including primary martian mantle melts and alkali basalts. The concentric cylinder method has been employed between 1500 °C and the respective liquidus temperatures of these liquids. The viscosity near the glass transition has been derived from calorimetric measurements of the glass transition. Although some glass heterogeneity limits the accuracy of the data near the glass transition, it was nevertheless possible to determine the parameters of the non-Arrhenian temperature-dependence of viscosity over a wide temperature range (1500 °C to the glass transition temperature). At superliquidus conditions, the martian basalt viscosities are as low as those of the Fe-Ti-rich lunar basalts, similar to the lowest viscosities recorded for terrestrial ferrobasalts, and 0.5 to 1 order of magnitude lower than terrestrial tholeiitic basalts. Comparison with empirical models reveals that Giordano et al. (2008) offers the best approximation, whereas the model proposed by Hui and Zhang (2007) is inappropriate for the compositions considered. The slightly lower viscosities exhibited by the melts produced by low degree of mantle partial melting versus melts produced at high degree of mantle partial melting (likely corresponding to the early history of Mars), is not deemed sufficient to lead to viscosity variations large enough to produce an overall shift of martian lava flow morphologies over time. Rather, the details of the crystallization sequence (and in particular the ability of some of these magmas to form spinifex texture) is proposed to be a dominant effect on the viscosity during martian lava flow emplacement and may explain the lower range of viscosities (10 2-10 4 Pa s) inferred from lava flow morphology. Further, the differences between the rheological behaviors of tholeiitic vs. trachy-basalts are significant enough to affect their emplacement as intrusive bodies or as effusive lava flows. The upper range of viscosities (10 6-10 8 Pa s) suggested from lava flow morphology is found consistent with the occurrence of alkali basalt documented from in situ analyses and does not necessarily imply the occurrence of basaltic-andesite or andesitic rocks