Psephitic deposits slope sediments of cryogene nature - block streams, widespread in the Kodaro-Udokan mountain area (the Northern Zabaikalye), are the object of our investigation over many years.
Mean height of snow cover for the period of its lying (8.5 - 9 months from the first ten-day period of September up to the middle of June), according to data of many years, is 30-50 cm in prebald peak belt of the Udokan ridge and 80-102 cm in bald peaks. Distinctions in moistening the slopes of different orientation are rather essential, i.e. height of snow cover varies greatly in relation to slope exposition height of snow cover in January reaches 17-20 cm and at the slope of north exposition - 43-47 cm.
Character of the underlying surface (High degree of hollow of psephitic sediments block streams cover) exerts a significant influence on forming the value ?7D?0 tch. in the equation of surface temperature regime. From January till March at decreasing the power of surface cover (at the sacrifice of snow evaporation and its melting while radiative thaws) a great decreasing of its warming influence (by 1.2 - 2 degrees) takes place, when the total value of this influence in the prebald peak belt is 5.8 degrees and in bald peaks - up to 8.4 degrees.
Snow falls on cover of block streams in consequence of blow in hollows at snowstorms and drop of snow mass under the influence of its own weight. It is often in this case that snow fills totally or almost totally hollows between rubbles.
In snow cover (and on the surface of block stream and in cover hollows) along with mechanical thickening (snow settles down and presses under the influence of gravity) intensive processes of metamorphism take place. These changes take place just as a result of cold type of metamorphic ice formation - at sublimation metamorphism and recrystallization, so as a result of "warm" type of metamorphic ice formation - at regelation recrystallization.
Stratigraphy of snow mass of block streams greatly differs from the structure of snow cover of finely divided grounds. High temperature and moisture gradients due to peculiarities of radiation-heat balance of block streams surfaces signify that in snow mass in the end of winter and spring (during radiative thaws even at negative temperatures) sublimation and vapor sublimate take place almost constantly. While that, grains of fine-grained snow enlarge modify and pass into friable aggregates of depth rime and ice crystals. Porosity of snow surface decreases in this case. Later on at recrystallization and local diffusion of vapor transformation of primary crystals into firn grains takes place. But in snow mass there are snow-ice crusts and interlayers (sometimes 2-3 cm in one cut), preventing the vapor introduction from below. In this case sublimate of crystals is changed by condensation of moisture draining in depth of the block stream. Part of this water getting into the snow in block streams hollows takes part in its recrystallization with formation of regelation firn and ice.
Considered peculiarities of dynamics, properties and stratigraphy of snow surface of psephitic slope deposits greatly influence on season freezing and thawing of block streams.
Irina Y. Malchikova Institute of Natural Resources P.O. Box 147 Butina, 26. Chita, Russia, 672090 Phone: 8-(30222)-6-73-17 Fax: 8-(30222)-1-25-82 E-mail: MEH@cinr.chita.su