The role of volcanological factors in controlling the types, form, residence time and amount of volcanic emissions cannot be underestimated. Magma chamber conditions, plumbing, magma type, crystal and volatile contents and vent environment will determine the magma rheology, magma fragmentation, composition, size and shape distribution of the erupted material and eruption style. Eruptions can vary from effusive activity to devastating explosive activity. Minor explosive eruptions produce moderate amounts of volatiles and small volcanic particulates which will have a high but localised impact. Emplacement of highly-unstable lava domes produce emissions enriched in crystalline silica that is preferentially released during dome-collapse eruptions. At the other end of the scale, major plinian eruptions can generate eruption columns an pyroclastic flows which form giant ash clouds, dispersing fine ash over millions of square kilometres.
Magma fragmentation mechanics controls the production, abundance and grain size of ash produced. The controls which affect the widespread dispersal of the finest ash need to be better understood. Controls on eruption duration also need to be identified and are directly relevant to the assessment of exposure to volcanic health hazards. For example, the factors that control duration of lava dome eruptions are little understood - some eruptions continue for decades whereas other only last some months. The presence of water vapour, droplets, or ice in eruption clouds affects the rates of aggregation and sedimentation of fine ash, and removal and oxidation of volatile species thereby impacting upon the environment and health.
These controls are tested and understood through direct and indirect observations (eg. remote sensing), theoretical and numerical modelling and laboratory experiments. The collection of extensive datasets is needed to constrain inverse and forward modelling, to relate deposits or data on dispersal to fundamental processes and to forecast potential hazards for human and animal health.
Download our pamphlets on preparing for ashfall and on the health hazards of ash. They are designed for mass distribution at the onset of new eruptions. They are now avaiable in English, Japanese, French Spanish, Portuguese, Swahili, Indonesian and Icelandic with Italian versions being available shortly. Please see our Pamphlets page for further infomation.