Abstract
The nature of the alteration of basaltic, andesitic and rhyolitic glass of Holocene and
Pleistocene age and their physical and chemical environments have been investigated in the ash
layers within the cryogenic soils associated with the volcanoes in the central depression of
Kamchatka. One of the main factors controlling the alteration of the volcanic glass is their initial
chemistry with those of andesitic (SiO2 = 5365 wt.%) and basaltic (SiO2 < 53 wt.%) compositions
being characterized by the presence of allophane, whereas volcanic glass of rhyolitic composition
(SiO2>65 wt.%) are characterized by opal. Variations in the age of eruption of individual ashes, the
amount and nature of the soil water, the depth of the active annual freeze-thawing layer, the thermal
conductivity of the weathering soils, do not play a controlling role in the type of weathering products
of the ashes but may affect their rates of alteration.
Pleistocene age and their physical and chemical environments have been investigated in the ash
layers within the cryogenic soils associated with the volcanoes in the central depression of
Kamchatka. One of the main factors controlling the alteration of the volcanic glass is their initial
chemistry with those of andesitic (SiO2 = 5365 wt.%) and basaltic (SiO2 < 53 wt.%) compositions
being characterized by the presence of allophane, whereas volcanic glass of rhyolitic composition
(SiO2>65 wt.%) are characterized by opal. Variations in the age of eruption of individual ashes, the
amount and nature of the soil water, the depth of the active annual freeze-thawing layer, the thermal
conductivity of the weathering soils, do not play a controlling role in the type of weathering products
of the ashes but may affect their rates of alteration.
