Geochemical Behavior of Iron in Noboribetsu Hydrothermal Activity

Abstract

Geochemical behavior of iron in Volcano Noboribetsu is described in this paper. In this active volcano, iron is introduced into thermal water derived from two origins, i.e. from chemical weathering of wall rock on the bottom of two explosion crators and from high-temperature and pressure thermal water enriched by iron derived from unknown magmatic reservoir on which the present volcanic activity depends.261 kg of iron is extracted by sulfuric acid every day from wall rock in Death Valley, one of two crators. And 100 kg of iron is transported from unknown magmatic reservoir with the thermal water through two chemical phases, i.e. the thermal water itself and bubble form of molten sulfur which is found at the bottom of Lake Oyunuma, the other crator. Molten sulfur has been separated from the thermal water and has extracted most of iron contained in the mother water.261 kg of iron corresponds to 4 ton of fresh wall rock. That is, 1.5 × 103 ton of wall rock has been decomposed every year in Death Valley and run off the valley. Chemical wathering, therefore, must have played an important role in forming up the present topographic feature of the crator.Amount of iron from unknown magmatic reservoir has been changed with a regularity in accordance with small volcanic explosion occurred therein.