tephra, ash
definition:
Volcanic ash consists of tiny jagged pieces of rock and glass. Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water. Ash is spread over broad areas by wind.
All explosive volcanic eruptions generate tephra, fragments of rock that are produced when magma or or rock is explosively ejected. The largest fragments, blocks and bombs, can be expelled with great force but are deposited near the eruptive vent. Ash is the most frequent, and often widespread, volcanic hazard and is produced by all explosive volcanic eruptions.
As a result of its fine-grained abrasive character and widespread distribution by wind, ashfall and volcanic ash clouds are a major hazard.
Ash particles can be carried hundreds or even thousands of kilometres away from source falling out of suspension over large multi-national areas to form ‘ash falls’, one of the volcanic hazard with the greatest potential to directly or indirectly affect the largest number of people worldwide (Simkin et al., 2001; Witham, 2005).
History:
The 2010 eruption of Eyjafjallajokull in Iceland highlighted the impacts of volcanic ash fall in modern society and our dependence on the functionality of infrastructure services. During this event the airline industry suffered business interruption losses of €1.5–2.5 billion from the closure of European airspace for six days in April 2010 and subsequent closures into May 2010.
Ashfall rarely endangers human lives, but it can have devastating effects on impact on livelihoods and socio-economic activities.
Fine grained ash, when ingested can cause health impacts to humans (deseases) and animals(deaths).
Ash fallout to the ground can pose significant disruption and damage to buildings, transportation, water and wastewater, power supply, communications equipment, agriculture, and primary production leading to potentially substantial societal impacts and costs, even at thicknesses of only a few millimetres or inches.
acid rain
volcano gases
changing meteo conditions
Other hazards:
Some of this volcanic ash mills around the air, joining other dust particles in the atmosphere as condensation nuclei, can even add enough volcanic ash cloud cover to the upper atmosphere to drop global temperature by several degrees while the particles spread slowly over the entire planet. For instance, the 1883 eruption of Krakatoa lowered global temperatures by 2.2 degrees
monitoring
Impacts from ashfall are more complex and multi-faceted than for any of the other volcanic hazards. Probabilistic methods are particularly important for determining volcanic ash fall hazard because the range of potential magnitudes, styles and external factors, such as wind conditions, may be large.
Assessment
Simulating historical scenarios can be useful for model calibration and for assessing what could happen if a wellknown eruption took place in a modern day setting. Due to the complexities involved in forecasting ash dispersion and deposition (like winds, weather conditions), algorithms and numerical models are employed.
in case of:
Use goggles and wear eyeglasses instead of contact lenses. Use a dust mask or hold a damp cloth over your face to help with breathing. Stay away from areas downwind from the volcano to avoid volcanic ash. Stay indoors until the ash has settled unless there is a danger of the roof collapsing.
Sources
https://en.wikipedia.org/wiki/Volcanic_ash
https://science.howstuffworks.com/nature/natural-disasters/volcanic-ash.htm
https://www.gns.cri.nz/Home/Learning/Science-Topics/Volcanoes/Volcanic-Hazards/Lahar
