Major processes controlling the existence of a large sub-continental glacier system were identified on the basis of glaciological, meteorological and isotopic analyses using expeditionary and long-term data. Observations were made on the southern Inylchek glacier located in the Pobeda-Khan Tengry massif, the largest sub-continental glacier system on the northern periphery of central Asia. More than 1200 glaciers with a total area of about 4320 km2 comprise the massif. Melt is for the most part caused by radiation and is most intensive during periods of anticyclonic weather with fohn development. The proportion of solar radiation input in relation to heat balance is more than 90%. Evaporation and condensation are negligible during most times and comprise 7% of heat expenditure. Accumulation was associated with cold cyclonic weather. Four ice-formation zones were identified, the upper boundary of liquid runoff is at 5200 m and the recryslallization zone is above 5900 m. The calculated net glacier mass is negative, −318 kg m−2 a−1, and indicates the degradation of modern Pobeda-Khan Tengry glaciers.