Eruptions from Ruapehu Volcano on 11 and 14 October 1995 and 17 June 1996 distributed at least 36 x 10⁶ m³ of sulphur(S)-rich tephra over the central and eastern North Island of New Zealand. The tephras added between 30-1500 kg ha^-1 S to at least 25,000 km² of land in primary production. Smaller but beneficial amounts of selenium (Se) and in some areas potassium and magnesium were also supplied. Addition of S to the soils in the form of sulphate and elemental S resulted in a drop in soil pH and an increase in pasture S contents within seven weeks of the eruptions. The soils affected by the tephra are naturally low in S and Se, but following the eruptions S was not required in fertilizer applications in many areas. The strongest and longest lasting effects of S and Se deposition were in high anion-retention soils particularly Hapludands (moist, moderately weathered soils, derived from volcanic ash). Soluble fluorine concentrations within the tephras were low compared to historic Icelandic and Chilean examples. However, pastoral livestock deaths were apparently caused by fluorosis in addition to starvation when tephra covered feed. The Ruapehu tephra contained very low concentrations of other soluble toxic elements.

Key words: Fluorosis; Ruapehu volcano; Selenium; Sulphur; Tephra; Volcanic hazards.

Reprints: S J Cronin, Massey University,
Department of Soil Science, Palmerston North, New Zealand.

COMMENT

There have been other reports of fluorosis in animals resulting from this eruption (e.g. see abstract in Fluoride 31 (1) pages 51-52 February 1998). Strangely, the medical literature mentions no effects of fluoride on humans inhabiting the same area. There were, however, complaints of distress, as the following abstract shows.

John Colquhoun

FLUORIDE 31(4),  1998, p 223	International Society for Fluoride Research
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