A new portable penetrometer for measuring the viscosity of active lava

• Published in: Review of Scientific Instruments
• Main Authors: Harris, M, A, Kolzenburg, S., Sonder, I., Chevrel, Oryaëlle
• Other Authors: University at Buffalo SUNY (SUNY Buffalo), State University of New York (SUNY), Laboratoire Magmas et Volcans (LMV), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA), Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris (IPG Paris)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2024
• Subjects: Measuring instruments; Thermocouples; Volcanology; Rheological instrumentation; Rheology and fluid dynamics; Rheological properties; Viscosity measurements; [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology; Hrútur; Iceland
• Online Access: https://hal.science/hal-04663298; https://hal.science/hal-04663298/document; https://hal.science/hal-04663298/file/Harris,%20M_et_al_2024%20Manuscript_revised_clean.pdf; https://doi.org/10.1063/5.0206776

International audience Viscosity is a fundamental physical property of lava that dictates style and rate of effusive transport. Studies of lava viscosity have predominantly focused on measuring re-melted rocks in the laboratory. While these measurements are well-constrained in temperature, shear rate, and oxygen fugacity, they cannot reproduce the complexities of the natural emplacement environment. Field viscosity measurements of active lava are the only way to fully capture lava’s properties, but such measurements are scarce, largely due to a lack of easy-to-use, portable, and accurate measurement devices. Thus, there is a need for developing suitable field instruments to help bolster the understanding of lava. Here, we present a new penetrometer capable of measuring a material’s viscosity under the harsh conditions of natural lava emplacement. This device uses a stainless-steel tube with a semi-spherical tip fixed to a load cell that records axial force when pushed into a material, while simultaneously measuring the penetration depth via a free-moving tube that is pushed backward along the penetration tube. The device is portable (1.5 m long, 5.5 kg in weight) and uses a single-board computer for data acquisition. The penetrometer has an operational range from 2.5 × 102 to 2.1 × 105 Pa s and was calibrated for viscosities ranging from 5.0 × 102 to 1.6 × 105 Pa s. It was deployed to the 2023 Litli-Hrútur eruption in Iceland. These field measurements successfully recorded the in situ viscosities of the lava in the range of 1.2 × 104–3.4 × 104 Pa s, showcasing it as an efficient method of measuring natural lava viscosity.