This is the first petrophysical study of extrusive rocks (dacites to andesites) discharged by Bezymianny Volcano. We provide a comparative description of properties for extrusive rocks in accordance with identified age groups. We show the dynamics in the variation of extrusive rock properties in relation to their ages, with the result that the older a rock the higher are its density, strength, and elastic parameters. Rocks petrophysical features are compared between extrusive domes and lava flows. We argue for petrophysical properties to be applicable for deriving more accurate results for the genesis of rocks having similar petrophysical properties, in particular, rocks of extrusive and effusive origin.

Представлены результаты исследования лавовых потоков вулкана Безымянный различного возраста - от древних (около 3500 лет назад) до современных (1985-1989 гг.). Приводится подробная характеристика состава, строения и петрофизических свойств основных типов слагающих их пород - андезитов и андезибазальтов. Установлено, что главным фактором, определяющим свойства пород, является их пористость; влияние структурно-минералогических особенностей проявляется в меньшей степени. Показана динамика изменения свойств пород лавовых потоков в зависимости от их возраста: чем древнее породы, тем выше показатели их плотности и прочности и ниже значения пористости.

Abstract—This paper discusses patterns that are observable in the alteration of effusive rocks that were discharged by Baranskii Volcano (central Iturup Island) under the action of sulfate chloride as well as acidic and ultra-acidic water (in the Kipyashchaya Rechka thermal brook). We acquired data on changes in the chemical and mineralogic composition of the rocks, structural features, porosity, and petrophysical properties. The dynamics of leaching and the leaching phase in a flowing acidic (ultra-acidic) geothermal environment are described. We note that the mechanism that is responsible for hydrogen sulfate leaching of rocks at the ground surface may be largely analogous to the generation of secondary quartzites (mono-quartzites) in the zones of ascending acidic gas flows above small gabbro–diorite and diorite intrusions.

The paper shows that the abnormally low values of longitudinal wave velocities, typical even for dense differences, are an important feature of Holocene effusive rocks of medium-basic composition. In order to explain this phenomenon, a series of experiments was conducted to saturate the samples with a phosphor followed by a study of the structure of the pore-fractured space on a fluorescent microscope. The experiments showed that low P-wave velocities are caused by the network of the finest microcracks formed in the rock during cooling and crystallization of the magmatic melt.