Application of vertical electrical sounding method to differentiate low terraces of the Lena river near Yakutsk

Abstract

The author proposes to consider the of electrical resistivity as a new indicator for solving one of the problems of geomorphology confirming or rejecting the hypothesis that the geomorphological appearance of the valley of the Lena River "Tuimaada", where Yakutsk is located, consists of not one, but two low floodplain terraces. To solve this problem, the data of the vertical electrical sounding method were used. With a small but statistically significant difference in the sample estimates of the average resistances, they naturally grow when moving from the first Yakut terrace to the higher second Sergelyakh terrace within the entire Tuymaada valley. Based on the data of engineering and geological surveys, the difference in the average estimates of the resistances of above-floodplain terraces is explained by the variability of the structure of frozen sands. In this variability the dominant factor is the factor of material composition, which generates a significant variability in the physical and mechanical properties of the sands along with the insignificant effect of factors and thermal, cryogenic state. According to the survey data, during the transition from the Yakut to the Sergelyakh terrace, fine-grained sands are replaced by older medium-grained sands with a natural decrease in the average indicators of total humidity, porosity and density growth of the mineral skeleton. Statistical analysis of the data of the electric sensing method confirms both the hypothesis put forward and the ideas of the predecessors of geomorphologists. Exactly, the Tuimaada valley consists not of one, but of two low terraces of different heights above the floodplain. The reliability of probabilistic and statistical solutions on which the conclusion is based is quite high and does not fall below 70 %.