Abstract

Aqueous sulfur speciation of samples of crater lake water from Crater Lake collected at Mt. Ruapehu, New Zealand since 1968 has been determined using high-performance liquid chromatography. Polythionates (S x O 6 2− ) are produced in the lake through reactions between sulfur dioxide and hydrogen sulfide gases from the subaqueous fumaroles. Their concentrations vary from 0 to a few hundred mg/l, corresponding to the activity of the volcano. The concentration of the total polythionates ( Σ S x O 6 2− = S 4 O 6 2− + S 5 O 6 2− + S 6 O 6 2− ) is found to be a good indicator of changes in the subaqueous fumarolic activity at Crater Lake. The molar S x O 6 2− /Cl − ratios of the lake water can be used to divide the volcanic activity of Crater Lake into four stages: 1. Stage I: Period of weak volcanic activity with no hydrothermal explosions. This stage is characterized by low total S x O 6 2− with a distribution order of S 5 O 6 2− > S 4 O 6 2− > S 6 O 6 2− . H 2 S is predominant among dissolved gases in the lake water. 2. Stage IIa: Quiescent period with minor hydrothermal explosions. The lake water contains high ΣS x O 6 2− with a distribution order of S 5 O 6 2− > S 4 O 6 2− > S 6 O 6 2− . Dissolved H 2 S and SO 2 gases are very low. 3. Stage IIb: Increased fumarolic activity with frequent hydrothermal explosions. Low ΣS x O 6 2− with a distribution order of S 4 O 6 2− > S 5 O 6 2− > S 6 O 6 2− . Sulfur dioxide but no H 2 S is detected in the water. 4. Stage III: Period of phreatomagmatic eruptions with lahars and intensive seismic activity. No S x O 6 2− exists but dissolved SO 2 is high in the lake water. The moderate-sized explosion of December 8, 1988, which was not preceded by any changes in lake water polythionate chemistry or seismic activity, is hypothesized to be a vent-cleaning eruption caused by blockage of ascending magmatic gases that was caused by solidification of a molten sulfur pool at the bottom of Crater Lake.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call