Abstract
Permafrost constrains certain limitations on physical and chemical processes occurring in the frozen and seasonal frozen grounds namely the weathering processes, organic matter, alteration of minerals and so on. The area of our interest was Kluchevskaya volcano group on Kamchatka peninsula of eastern Russia; there the mountain permafrost is widespread. The most part of Kamchatka Peninsula is covered by with soil-pyroclastic cover which is consists of tephra horizons and buried soils. Pyroclastic ash is the least stable solid phase of sediments that is predisposed to different mineral transformation in all lithogenetic stages. Among the alteration products caused by weathering and diagenesis are smectites, halloysite, kaolinite, allophane, palagonite and others. The alteration processes of volcanic glass are complicated and phasic.
The objectes of our investigation were samples of volcanic ash collected from different attitudes and are the products of different volcanoes. The age range was from 35 to 250000 years old. According to silicon dioxide volcanic glass in samples can be divided to three types: andesite, basalt and rhyolite. The mineral composition was observed using IR-spectrometer. IR-spectra indicates that amorphous allophane is associated with andesitic and basaltic glass whereas opal with rhyolitic glass. Opal is hydrated silicon dioxide. Allophane is hydrous aluminium silicate amorphous clay mineral and is the product of volcanic glass alteration.
It is reported that in arid regions – New Zeland - rhyolitic and andesitic volcanic glasses weather to allophane at widely different range. Whereas glass in the clay fractions of rhyolitic tephra alters to allophane after about 3000 years, very little glass remains in the clay fractions of andesitic tephra which are only 300 years old. But in cold severe regions – Kamchatka – we found out that in rhyolitic tephra even after 250 000 years there is no alteration to allophane.
Because the cold climate and existence of permafrost, the weathering process in Kamchatka’s soils has a very low rate. These conditions do not allow glass alteration processes to go farther so halloysite, kaolinite and other clay minerals do not develop from short-range-order alumosilicates (allophane etc). So, IR-spectroscopy shown that in basaltic pyroclastic deposits there is waterless allophane presence even after 35 years but in rhyolitic pyroclastic even after 15000-250000 years there is opal presence.
Also we observed the role of allophane and opal appearance on thermal conductivity (λfr, W/(m•K)) of frozen volcanic ashes. We make generalization of thermal conductivity results on humidity degree (Sr, units). It was found that the highest thermal conductivity is in the ash samples with opal and rhyolitic volcanic glass, lowest – in ones with allophane and andesitic - basaltic glass. For practical use thermal conductivity can be calculated from these correlations: λfr = 1,193 *Sr + 0,153 (for opal ashes) and λfr = 0,895 *Sr + 0,142 (for allophane ashes).
The objectes of our investigation were samples of volcanic ash collected from different attitudes and are the products of different volcanoes. The age range was from 35 to 250000 years old. According to silicon dioxide volcanic glass in samples can be divided to three types: andesite, basalt and rhyolite. The mineral composition was observed using IR-spectrometer. IR-spectra indicates that amorphous allophane is associated with andesitic and basaltic glass whereas opal with rhyolitic glass. Opal is hydrated silicon dioxide. Allophane is hydrous aluminium silicate amorphous clay mineral and is the product of volcanic glass alteration.
It is reported that in arid regions – New Zeland - rhyolitic and andesitic volcanic glasses weather to allophane at widely different range. Whereas glass in the clay fractions of rhyolitic tephra alters to allophane after about 3000 years, very little glass remains in the clay fractions of andesitic tephra which are only 300 years old. But in cold severe regions – Kamchatka – we found out that in rhyolitic tephra even after 250 000 years there is no alteration to allophane.
Because the cold climate and existence of permafrost, the weathering process in Kamchatka’s soils has a very low rate. These conditions do not allow glass alteration processes to go farther so halloysite, kaolinite and other clay minerals do not develop from short-range-order alumosilicates (allophane etc). So, IR-spectroscopy shown that in basaltic pyroclastic deposits there is waterless allophane presence even after 35 years but in rhyolitic pyroclastic even after 15000-250000 years there is opal presence.
Also we observed the role of allophane and opal appearance on thermal conductivity (λfr, W/(m•K)) of frozen volcanic ashes. We make generalization of thermal conductivity results on humidity degree (Sr, units). It was found that the highest thermal conductivity is in the ash samples with opal and rhyolitic volcanic glass, lowest – in ones with allophane and andesitic - basaltic glass. For practical use thermal conductivity can be calculated from these correlations: λfr = 1,193 *Sr + 0,153 (for opal ashes) and λfr = 0,895 *Sr + 0,142 (for allophane ashes).
