Dense Gas Dispersion and Modelling at Fagradalsfjall, Iceland

Lead Research Organisation: University of Leeds
Department Name: National Centre for Atmospheric Science


The ongoing eruption at Fagradalsfjall in Iceland presents an outstanding and rare opportunity to observe and model the behaviour of dense volcanic gases. Sulphur Dioxide (SO2) is the principal emission from lava-rich eruptions such as at Fagradalsfjall. With more than double the molecular weight of air, this is prone to exhibiting dense gas dispersion characteristics such as settling, with the potential to significantly affect the dispersion over scales of hundreds of kilometers. This can lead to enhanced concentrations at low levels with consequences for air quality and human health.

This project aims to (a) collect a surface air quality and meteorological dataset and (b) produce a modelling framework capable of simulating dense gas and validate it against (a). Such a framework does not exist at present. This is a significant, time-limited and accessible eruption event which, if responded to now, can lead to major advances in both scientific understandings and in the management of future, possibly larger, eruptions from which there is a serious gas hazard.

(A) We will enhance existing air quality observations in the vicinity of Fagradalsfjall, creating a network to provide a comprehensive assessment of dense volcanic gas dispersion on a scale of 50-100 km. This unique dataset will provide the first independent verification for a full meteorological prediction model with dense gas capability coupled with surface heating (see below).

(B) Recent model development work has demonstrated effective volcanic gas dispersion predictions using an adapted version of the NCAR Weather Research and Forecasting (WRF) model. This system was used to successfully interpret aircraft measurements of CO2 dispersion from the (subglacial) Katla volcano in Iceland and to explain quantitatively, for the first time, the dense gas CO2 behaviour which led to the Lake Nyos disaster in 1986 that saw dense CO2 pooling and draining down valleys, causing ~1700 deaths. Neither of these applications considered (or required) a heated surface. However, the Fagradalsfjall eruption is now in a phase where lava fountains have been reported, and so the effect of surface heating will need to be considered in any modelling, to include the complex interactions and feedbacks between a dense gas, a heated surface, and the underlying meteorology.

The model, after development and verification, will be available in the future as an operational hazard prediction system and and could lead to significant improvements in the UK national capability to respond to dense gas releases. This includes anthropogenic releases, for example industrial accidents and fires.


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Description Gases released over hot sources (such as volcanic vents) reach a height in the atmosphere that depends upon the density of the gas. This has been shown by an extensive series of high-resolution numerical experiments completed on the ARCHER2 supercomputer. A simple theoretical relation can be used to approximate this relation between density of gas, amount of heating at the surface, and the maximum height attained. This is important as many atmospheric dispersion programs - used to determine the spread of hazardous gases - require this maximum height as a key parameter.
Exploitation Route We plan to publish this work and when that is done, the simple theoretical relation mentioned above could be used by scientists running atmospheric dispersion programs to initialise their models. This is important for the simulation of the spread of hazardous gases.
Sectors Aerospace, Defence and Marine,Environment,Leisure Activities, including Sports, Recreation and Tourism

Description NAVHP 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The North Atlantic Volcanic Hazard Partnership (NAVHP) consists of experts from the National Centre for Atmospheric Science, The Met Office, The Icelandic Meteorological Office, the British Geological Service, and the London Volcanic Ash Advisory Centre. Partners discuss the best reposnses to volcanic hazards and the work in this grant relates to the forecasting of hazardoud gas dispersion. Work was presented at the Autumn 2022 meeting.
Year(s) Of Engagement Activity 2022,2023