Аннотация:This paper considers the mechanism of basalts transformation including chemical elements mobility, initial minerals substitution, structure and pore-space alterations, physical and mechanical characteristics alterations as a result of acid thermal water impact in the region of modern volcanic and geothermal activity (Iturup Island, Far East, Russia). Result from water/rock interaction basalts debris found on the bottom of thermal river acquire zonal structure. The boundaries between the zones are distinct. The water/rock interaction process is accompanied by stepped leaching of the most of chemical elements and by gain of silicon and sulphur. From inner to outer zones there are observed: decrease of initial minerals content along with increase of quartz-group minerals, increase of total and open porosity as well as pore-size, decrease of petrophysical parameters such as density, strength, acoustic rigidity. The sequence of substance transformation (as mineral as well as physical characteristics) is the same for all samples although the degree of alteration is different.
