While some 55 ionic species have been reported in fresh ash leachates the most abundant species usually found are the cations Na , K , Ca2 and Mg2 and the anions Cl − , F − and SO42 − . Molar ratios between ions present in leachates suggest that in many cases these elements are present as simple salts such as NaCl and CaSO4 . In a sequential leaching experiment on ash from the 1980 eruption of Mount St. Helens , chloride salts were found to be the most readily soluble , followed by sulfate salts Fluoride compounds are in general only sparingly soluble ( e.g. , CaF2 , MgF2 ) , with the exception of fluoride salts of alkali metals and compounds such as calcium hexafluorosilicate ( CaSiF6 ) . The pH of fresh ash leachates is highly variable , depending on the presence of an acidic gas condensate ( primarily as a consequence of the gases SO2 , HCl and HF in the eruption plume ) on the ash surface
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Volcanic ash