The following is the first technical report received from Mongolia. Additional infirmation may be obtained from the author
at the Institute of Geography and Geocryology, Mongolian Academy of Sciences, Ulanbator, Mongolia, 210620.
In 1992-93, in order to develop a new method to decrease the depth and duration of seasonal freezing in the area of the Baganuur coal deposit, N. Sharkhuu carried out temperature observations on freezing processes using insulation covers over gravels and sands. Sawdust 15 and 35 cm thick was used. The depth of seasonal freezing for gravel and sand was 4.1 m (moisture content 5%, mean annual temperature -2°C). The sawdust had a moisture content of 55% and a density of 0.17 g/cm3. The temperature observations give the following results: decrease of the date from the beginning of freezing and from the ending of thawing and reduction of the depth of seasonal freezing of ground for the sawdust covers with thickness of 35 cm to 2.6 m, with changes from 43 to 52 days. The results obtained show that this method is suitable for development of coal deposit earthworks under the conditions in Mongolia.
N. Sharkhuu obtained ground temperature regimes for the period 1991-93 in more than 20 boreholes in the Nalaikh coal deposit to depths of 20-100 m. As a result of the observations the author has elucidated ground temperature regimes for the seasonal thawing layers and permafrost and established the thickness and annual temperature of continuous permafrost in this deposit. In this area the permafrost is up to 45 m thick with an annual temperature from O° to -1°C. The depth of the active layer ranges from 2.2 to 4.8 m. All characteristics obtained are shown on the author's permafrost map of the Nalaikh deposit area at a scale of 1:5000. According to temperature data measured in borehole N23 over the period 1945-93, the rate of decrease of permafrost thickness from below (from subpermafrost exploitation of the deposit) was on the average 0.4 m/yr or a decrease from 50 m to 20 m for 48 years.
In 1993, geocryological field research was carried out on the Bajankhongor ritory, an area of 116,000 km2 that embraces the Kangai Mountains on the south. As a result of previous geocryological generalization and new research by N. Sharkhuu, D. Tumurbaatar and R. Lomborenchen, maps have been compiled of permafrost and seasonally freezing
and thawing soils, and also a map of the distribution of cryogenic processes and phenomena on a scale of 1:500,000. According to these maps, mean annual ground temperature ranges from -8°C to -1°C, permafrost thickness in the^Kangai Mountains reaches to some hundred meters, and the depth of seasonal freezing and thawing is from 1 to 5 m.
There is widespread occurrence of cryogenic processes and features, including frost mounds, surface icings, thermokarst and stone polygons.
Submitted by N. Sharkhuu