Andrew Tupper

A half-day workshop was held following the IAVCEI Scientific Assembly in Rotorua, New Zealand, on 5 February 2023, taking advantage of the presence of operationally focused meteorologists, leaders from the World Meteorological Organization and volcanologists (mostly from volcano observatories), for an aviation workshop over the previous two days. Our workshop focused on non-aviation issues but sought to develop the ‘big-picture’ of multi-hazard arrangements, particularly noting the intertwining of the disciplines for many volcanic hazards, and a global push towards better integrated, impact-based multi-hazard early warning systems; including especially the Sendai Framework and the ‘Early Warnings for All’ initiative. The hazards requiring joint multi-disciplinary arrangements include tsunamis, ashfall and airborne / water-borne ash, rainfall-induced dome collapses, lahars, pumice, glacial floods, and gas. Of these, only airborne ash for aviation users have received much attention. Following an afternoon of presentations, panel discussions, breakout discussion, two summary visualisations were prepared – a future ‘vision’ and a future ‘roadmap’ for multi-hazard operations. These are presented as input towards follow-up actions, including ensuring that volcanic ash for aviation arrangements are embedded within a holistic multi-hazard and multi-user approach.

Much work has been done to build arrangements between volcanology and meteorology to handle the aviation risks from volcanic ash. This workshop will discuss how to approach collaborative arrangements for other volcanic hazards to the public, particularly where a multi-disciplinary approach is required. These hazards include tsunamis, ashfall, rainfall-induced dome collapses, lahars, pumice, glacial floods, and gas. They threaten a range of sectors including marine users, land transport users, agriculture, and residential communities. Approaching these hazards in an integrated fashion with the hydrometeorological community will help provide consistent and coherent warnings, create a focus on the capacity development required, and ultimately build a safer world consistent with the Sendai Framework and the recent UN call to provide universal coverage for early warning systems.The workshop featured a range of multi-disciplinary presentations on this theme, and discuss and draft a vision for future seamless multi-hazard warnings for volcanic eruptions and for secondary hazards.

Understanding the location, intensity, and likely duration of volcanic hazards is key to reducing risk from volcanic eruptions. Here, we use a novel near-real-time dataset comprising Volcanic Ash Advisories (VAAs) issued over 10 years to investigate global rates and durations of explosive volcanic activity. The VAAs were collected from the nine Volcanic Ash Advisory Centres (VAACs) worldwide. Information extracted allowed analysis of the frequency and type of explosive behaviour, including analysis of key eruption source parameters (ESPs) such as volcanic cloud height and duration. The results reflect changes in the VAA reporting process, data sources, and volcanic activity through time. The data show an increase in the number of VAAs issued since 2015 that cannot be directly correlated to an increase in volcanic activity. Instead, many represent increased observations, including improved capability to detect low- to mid-level volcanic clouds (FL101–FL200, 3–6 km asl), by higher temporal, spatial, and spectral resolution satellite sensors. Comparison of ESP data extracted from the VAAs with the Mastin et al. (J Volcanol Geotherm Res 186:10–21, 2009a) database shows that traditional assumptions used in the classification of volcanoes could be much simplified for operational use. The analysis highlights the VAA data as an exceptional resource documenting global volcanic activity on timescales that complement more widely used eruption datasets.

Volcanic ash clouds often become multilayered and thin with distance from the vent. We explore one mechanism for development of this layered structure. We review data on the characteristics of turbulence layering in the free atmosphere, as well as examples of observations of layered clouds both near-vent and distally. We then explore and contrast the output of volcanic ash transport and dispersal models with models that explicitly use the observed layered structure of atmospheric turbulence. The results suggest that the alternation of turbulent and quiescent atmospheric layers provides one mechanism for development of multilayered ash clouds by modulating the manner in which settling occurs.

Volcanic ash clouds often become multilayered and thin with distance from the vent. We explore one mechanism for development of this layered structure. We review data on the characteristics of turbulence layering in the free atmosphere, as well as examples of observations of layered clouds both near-vent and distally. We then explore dispersion models that explicitly use the observed layered structure of atmospheric turbulence. The results suggest that the alternation of turbulent and quiescent atmospheric layers provides one mechanism for development of multilayered ash clouds by modulating vertical particle motion. The largest particles, generally $> 100 \mu$m, are little affected by turbulence. For particles in which both settling and turbulent diffusion are important to vertical motion, mostly in the range of 10-100 $\mu$m, the greater turbulence intensity and more rapid turbulent diffusion in some layers causes these particles to spend greater time in the more turbulent layers, leading to a layering of concentration. For smaller particles, mostly in the submicron range, the more rapid diffusion in the turbulent layers causes these particles to ``wash out'' quickly.