Geologic structure and fumarolic activity of the Esmeralda submarine volcano

International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.In 1978, geologic, geophysical and hydrochemical studies were conducted at the Esmeralda volcano on board the R. V. Vulkanolog during cruises 4 and 5. These studies revealed submarine fumaroles on a slope of the crater at a depth of 80 m. Hydrochemical sampling of a train of submarine fumaroles with a series of water bottles showed the anomalously high concentrations of dissolved silicic acid and the lower chlorinity. Studies on the dynamics and chemical composition of the anomalous water layer permitted elaboration of a procedure for evaluation of the rate and phase state of heat transfer and of neat discharge of the volcano. In January 1978, the heat transfer rate was at the minimum 1500 kg/s and the heat discharge was approximately (5-6) X 105 kcal/s; the heat transfer included approximately equal amounts of water and steam. Native sulphur and other fumarolic products and hydrothermally altered rocks were recovered by dragging near the submarine fumaroles. Fresh ferromanganesian incrustations and nodules were discovered in the upper part of the cone. Magmatic rocks are represented by aphyric and porphyric basalts, dolerite·basalts and gabbroids. Based on data of magnetic survey, the volcano is composed, mainly, of porphyric basalts. A sedimentary cover in the region of the Esmeralda volcano is represented exclusively by pyroclastic deposits. Their volumes were calculated using the results of seismic profiling. The main part of pyroclastic material is shown to be erupted and distributed in seawater.