Contact Us

Volcanic Ash, Gases & VogVolcanic AshGases & VogAcid RainWhat's it like during ashfall?Agriculture—Plants & AnimalsHealthBuildingsEquipment & CommunicationsPower SupplyTransportationWater & WastewaterCleanup, Disposal & ReuseRemobilisation–Long-Term AshPreparednessCitizen ScienceCase Studies

Volcanic Ash


Freshly‐erupted volcanic ash commonly has a surface coating of soluble salts and acids. This coating is formed when primary volcanic gases (such as the strong acids HCl and HF, and SO2 (which rapidly converts to sulphate aerosol and sulphuric acid) condense onto particles as the volcanic plume cools in the atmosphere. The acidic condensate can then interact with ash particle surfaces and release elements such as calcium and magnesium, which may then form a range of secondary salts.

pH

Ash surfaces may be strongly acidic (have a low pH) which may cause damage on direct contact, for example, acidic irritation of skin, eyes and mucous membranes and acidic damage to crops.

Soluble elements

A wide range of readily water soluble elements have been reported in fresh volcanic ash. The major species are calcium, magnesium, sodium, potassium, aluminium, chloride, fluoride and sulphate. In many cases, these elements are present as simple salts such as sodium chloride (NaCl) or calcium sulphate, or gypsum (CaSO4). The release of these elements may be beneficial to the environment (e.g. if soil nutrients such as sulphur are added) or harmful (if potentially toxic elements such as fluorine are ingested by livestock grazing on ash-covered feed).

The table below shows ash leachate compositions for a range of eruptions.  

Table showing concentrations of leachable constituents in ashfall from some historic eruptions (all concentrations in mg/kg).
Fuego, Guatemala Pacaya, Guatemala Santiaguito, Guatemala Mt. St. Helens, USA Ruapehu, New Zealand
Element Mean Max Mean Max Mean Max Mean Max Median Max
Al 5.2 26.8 12.8 21.2 5.2 19.6 - - 42.8 1160
B 0.088 0.044 0.06 0.108 1.08 3.92 - - - -
Ba 0.296 1 0.68 1.12 0.132 0.348 0.152 0.24 - -
Br - - - - - - - - 1.6 13.6
Ca 400 1040 196 304 600 2240 440 800 1890 6760
Cd 0.008 0.04 0.056 0.128 0.056 0.256 0.0052 0.0252 - -
Cl 124 232 204 840 440 1400 392 668 248 2020
Co 0.0036 0.0328 0.0072 0.024 0.132 0.6 0.0196 0.072 - -
Cu 0.324 2.52 1.24 2.36 1.56 2.8 0.164 0.48 - -
F 21.2 88 28.8 44 14.4 23.2 7.2 12 25.8 95.6
Fe 2.08 22.4 2.8 9.2 1.56 3.6 0.376 0.48 5.74 92.8
K - - - - - - - - 36.1 253
Li 0.044 0.116 0.0036 0.064 0.4 1.88 0.208 0.52 0.5 1.45
Mg 22 44 19.6 52 96 400 48 84 235 1200
Mn 1.48 3.12 1 2.88 19.6 92 7.6 13.2 - -
Na 128 184 156 440 400 1760 264 440 292 1150
Pb 0.104 0.96 0.014 0.044 0.0096 0.048 0.0092 0.072 - -
Si 7.2 12.4 9.2 15.2 7.6 11.2 40 56 - -
Sr 2 5.2 1.64 2.6 1.48 4.4 1.76 2.88 - -
U 0.00108 0.0028 0.00008 0.00048 0.0012 0.006 0 0 - -
V 0.06 0.128 0.0248 0.068 0.0364 0.08 0.0012 0.0264 - -
Zn 0.144 0.56 5.6 18.8 2.04 8.4 2.04 26.8 - -
Nitrate                 21.9 88.9
Sulfate             1000 1800 5190 24530
Concentration values have been derived by Johnston et al (2004) both from data specific to Mt. Ruapehu (Cronin et al., 1998; Neild et al., 1998; Cronin et al., 2003, Christenson, 2000) and from data on ashfall composition from historic eruptions. Smith et al. (1982 and 1983) present data on leachable matter in ashfall for a range of volcanic systems: basaltic (1974 eruptions of Fuego and Pacaya) and dacitic (1969, 1975 and 1976 eruptions of Santiaguito, Guatemala, and 1980 eruption of Mt. St. Helens, U.S.A.).