Физическое моделирование контакта ледника с ложем (эксперименты)

Studies of the adhesive strength of glacial ice connection with bedrock has been studied using the analysis of the amplitude-frequency characteristics of acoustic emission (AE) in the frequency range from 15 Hz to 20,000 Hz. Identification of signal source on bed is based on physical modeling of adhesive ice fracture at the complex shear and patterns of elastic waves propagation in the ice using data on ice thickness of the ice and its acoustic properties. The experimental dependence of the ice and serpentinite substrate adhesive strength with temperature (from 0 °C to −30 °C) has been obtained at constraint axial shear. It is shown that the destruction of adhesive ice contact with substrate begins long before the maximum shear stress achieved, and AE signals in the coordinates amplitude-frequency-time have been obtained for the for static friction and sliding parts of deformation curves. Influence of shear to normal stresses ratio on the adhesive ice/substrate strength has been shown. Influence of the ratio of longitudinal and transverse shear stresses on the adhesive bond strength of ice to the substrate has been shown. The natural glacier spectra revealed periodic reduction of AE signals frequency in the middle range of frequencies. The similar effect of AE signals shifting along the frequency axis to the low frequency domain was obtained by testing of freshwater ice samples and related with expansion of the destruction scale. Practical application of the strain AE results for remote determination of the local glacial stability and for studies of glacier ice mechanics is discussed.Проведены комплексные исследования адгезионной прочности соединения льда с подложкой, предусматривающие анализ амплитудно-частотных характеристик сигналов акустической эмиссии (АЭ) в диапазоне частот от 15 до 20 тыс. Гц. Данные физического моделирования процессов адгезионного разрушения льда подтверждены результатами полевых исследований ледников Центральный Туюксу и Молодежный в Заилийском Алатау. Получена экспериментальная зависимость адгезионной прочности соединения льда с серпентинитом (подложкой) от температуры (от 0 до −25 °С) при осевом сдвиге в условиях стеснения. Показано, что адгезионный контакт лёд–подложка начинает разрушаться намного раньше достижения максимальных напряжений сдвига, причём для участков деформационных кривых (трение покоя и скольжения) получены диаграммы сигналов АЭ в координатах амплитуда–частота–время. Показано влияние соотношения продольных и поперечных сдвиговых напряжений на адгезионную прочность соединения льда с подложкой. В среднем диапазоне частот собственных акустических спектров ледников установлено периодическое уменьшение частоты заполнения сигналов АЭ. Аналогичный эффект смещения сигналов АЭ по оси частот в сторону низкочастотного диапазона получен при испытании образцов пресноводного льда и обусловлен расширением масштаба разрушения. Результаты исследований можно использовать для дистанционного изучения кинетики накопления трещин в придонных слоях ледникового льда

Условия на ложе и поверхности ледникового купола Вавилова (Северная Земля) во время его подвижки по данным аэрорадиозондирования

The glacier surge at Vavilov Ice Cap, Severnaya Zemlya, Russia (79°18′ N, 94°40′ E) began as early as the mid-1960s with a slow advance of its margin in the western part. Since 2012, the advance switched to the phase of catastrophic movement, which reached its climax in 2016, when the glacier velocity reached 9.2 km a‒1. An ice fan with an area of about 140 km2 advanced into the Kara Sea water area 11 km from the shore, and a strongly crevassed ice stream was formed in the ice cap itself, which continues to move now with speeds of about 2 km a‒1. The dynamic instability of Vavilov Ice Cap can be triggered by changes in basal conditions, which are still poorly known. In this study, we used airborne radio-echo sounding data acquired in September 2014 over the ice cap to characterize its surface and bedrock conditions. Based on the delay time and reflection amplitudes, the power reflection coefficient (PRC) from glacier surface and bedrock was estimated. For its calibration, we used the amplitude of reflections from the sea surface registered from different altitudes. The bedrock PRC values were converted to dielectric permittivity and compared with the glacier surface velocities in 2014 obtained from Landsat-7 images. We found a high positive correlation between the bedrock PRCs and velocities in the area with glacier speed higher than 1000 m a-1. In this area, the PRC is 20 dB higher than in the neighboring slower moving areas. Such a difference may be because the ice stream advanced on marine loose sediments with higher dielectric permittivity and conductivity and a higher reflection coefficient. The range of estimated bedrock PRCs corresponds to bed materials with relative dielectric permittivity from 5 to 10 and electrical conductivity from 10–5 to 10–2 Sm m‒1.По данным измерений времени запаздывания и амплитуд радиоотражений от ложа ледникового купола Вавилова, полученным в период быстрой подвижки его западной части, определены значения коэффициента отражения от ложа по мощности, которые коррелируют с высокими скоростями (более 1000 м/год) движения ледника в области, наступившей на участок мелководья

Толщина льда и снежного покрова ледника ИГАН (Полярный Урал) по данным наземного радиозондирования в 2019 и 2021 гг.

Small glaciers of the Polar Urals are at the limits of their existence. Their state and changes serve as an important natural indicator of modern climatic changes. In 2019 and 2021, we performed ground-based radar studies of one of these glaciers, the IGAN Glacier, to measure ice thickness and snow cover. We used PicorLed (1600 MHz), and VIRL–7 (20 MHz) GPRs. According to these data, the glacier has an average thickness of 49 m, maximum 114 m. The glacier has a polythermal structure: a cold ice layer with an average thickness of 12 m (maximum 43 m), overlaps the temperate ice with an average thickness of 37 m (maximum 114 m in the upper part of the glacier). The volume of ice contained in the glacier (in its studied part) is 14.3 × 106 m3, of which 10.89 × 106 m3 is temperate ice and 3.44 × 106 m3 is cold ice. For comparison: according to the radar data of 1968, the total ice thickness then reached 150 m in the central part, and the thickness of the upper layer of cold ice was 40–50 m. Radar snow gauge survey allowed to build schemes of seasonal snow thickness distribution over the glacier surface in 2019 and 2021, where there is a general spatial pattern of snow thickness growth from 2 m on the glacier terminus to 8 m or more to the rear wall of the corrie, which is due to the significant influence of avalanche feeding and wind transport. The glacier has lost about 3.2 × 106 m3 of ice per last decade, if the rate of loss continues, it may disappear in 40–50 years. However, this process may have a non-linear nature, as it involves not only climatic factors, but also local terrain features, on the one hand contributing to a high accumulation of snow, on the other – the formation of a glacial lake during glacier retreat, which may increase ablation.В 2019 и 2021 гг. на леднике ИГАН проводились георадарные измерения толщины льда (ВИРЛ-7, 20 МГц) и снежного покрова (Пикор-Лёд, 1600 МГц). Показано, что ледник имеет политермическую структуру, а его толщина достигает 114 м. Выполнена оценка величины и особенностей распределения снежной толщи по площади ледника и прилегающей территории

ТОЛЩИНА СНЕЖНОГО ПОКРОВА НА ЛЕДНИКЕ ВОСТОЧНЫЙ ГРЁНФЬОРД (ШПИЦБЕРГЕН) ПО ДАННЫМ РАДАРНЫХ ИЗМЕРЕНИЙ И СТАНДАРТНЫХ СНЕГОМЕРНЫХ СЪЁМОК

Summary Comparison of two methods of measurements of snow cover thickness on the glacier Austre Grønfjordbreen, Svalbard was performed in the spring of 2014. These methods were the radar (500 MHz) observations and standard snow surveys. Measurements were conducted in 77 different points on the surface of the glacier. A good correlation (R2 = 0.98) was revealed. In comparison with the data of snow surveys, the radar measurements show a similar but more detailed pattern of the distribution of the snow cover depth. The discrepancy between the depths of snow cover on maps plotted from data of both methods did not exceed 30 cm in most parts of the glacier. The standard error of interpolation of the radar data onto the entire glacier surface amounts, on average, to 18 cm. This corresponds to the error of radar measurements of 18.8% when an average snow depth is about 160 cm and 9.4% at its maximum thickness of 320 cm. The distance between the measurement points at which the spatial covariance of the snow depth disappears falls between 236 and 283 m along the glacier, and between 117 and 165 m across its position. We compared the results of radar measurements of the pulse-delay time of reflections from the base of the snow cover with the data of manual probe measurements at 10 points and direct measurements of snow depth and average density in 12 snow pits. The average speed of radio waves propagation in the snow was determined as Vcr = 23.4±0.2 cm ns−1. This magnitude and the Looyenga and Kovacs formulas allowed estimating the average density of snow cover ρL = 353.1±13.1 kg m−3 and ρK = 337.4±12.9 kg m−3. The difference from average density measured in 12 pits ρav.meas = 387.4±12.9 kg m−3 amounts to −10.8% and −14.8%. In 2014, according to snow and radar measurements, altitudinal gradient of snow accumulation on the glacier Austre Grønfjordbreen was equal to 0.21 m/100 m, which is smaller than the average values (0.35 m/100 m). According to the results of snow measurements of 2011–2014, the average thickness of the snow cover on the glacier Austre Grønfjordbreen was by 17 cm greater than in 1979. In the very snowy year 2012, it was higher by 21.5 cm in comparison with the year 1979, and its spatial variability (standard deviation σН) had increased by 25.6 cm. Estimates of spatial and temporal variability of snow cover depth will be used to analyze the hydrothermal state of the glacier and its changes with regard to revealed features and climatic trends.Приведены результаты измерений толщины снежного покрова на леднике Восточный Грёнфьорд (Шпицберген) весной 2014 г. По этим данным оценена точность радиолокационных измерений толщины и средней плотности снежного покрова, а также их пространственная и временнáя изменчивость по сравнению со снегомерными измерениями 2011–2014 и 1979 гг

Regularidades globales de la distribución del consumo de recursos versus Producto Nacional Bruto en economía.

High resource consumption in the economies of many countries of the world allows the appearance of serious and important problems for mankind: depletion of some natural resources, pollution of the environment, low economic efficiency and political controversies among states and regions.El elevado consumo de recursos en las economías de muchos países del mundo favorece el surgimiento de importantes y graves problemas para la humanidad, como el agotamiento en el futuro de algunos recursos naturales, el deterioro del medio ambiente, la baja eficiencia económica y, a veces, las disputas políticas entre estados y regiones

Physical modeling of glacier contact with bedrock (experiment)

Studies of the adhesive strength of glacial ice connection with bedrock has been studied using the analysis of the amplitude-frequency characteristics of acoustic emission (AE) in the frequency range from 15 Hz to 20,000 Hz. Identification of signal source on bed is based on physical modeling of adhesive ice fracture at the complex shear and patterns of elastic waves propagation in the ice using data on ice thickness of the ice and its acoustic properties. The experimental dependence of the ice and serpentinite substrate adhesive strength with temperature (from 0 °C to −30 °C) has been obtained at constraint axial shear. It is shown that the destruction of adhesive ice contact with substrate begins long before the maximum shear stress achieved, and AE signals in the coordinates amplitude-frequency-time have been obtained for the for static friction and sliding parts of deformation curves. Influence of shear to normal stresses ratio on the adhesive ice/substrate strength has been shown. Influence of the ratio of longitudinal and transverse shear stresses on the adhesive bond strength of ice to the substrate has been shown. The natural glacier spectra revealed periodic reduction of AE signals frequency in the middle range of frequencies. The similar effect of AE signals shifting along the frequency axis to the low frequency domain was obtained by testing of freshwater ice samples and related with expansion of the destruction scale. Practical application of the strain AE results for remote determination of the local glacial stability and for studies of glacier ice mechanics is discussed

SNOW THICKNESS ON AUSTRE GRØNFJORDBREEN, SVALBARD, FROM RADAR MEASUREMENTS AND STANDARD SNOW SURVEYS

Summary Comparison of two methods of measurements of snow cover thickness on the glacier Austre Grønfjordbreen, Svalbard was performed in the spring of 2014. These methods were the radar (500 MHz) observations and standard snow surveys. Measurements were conducted in 77 different points on the surface of the glacier. A good correlation (R2 = 0.98) was revealed. In comparison with the data of snow surveys, the radar measurements show a similar but more detailed pattern of the distribution of the snow cover depth. The discrepancy between the depths of snow cover on maps plotted from data of both methods did not exceed 30 cm in most parts of the glacier. The standard error of interpolation of the radar data onto the entire glacier surface amounts, on average, to 18 cm. This corresponds to the error of radar measurements of 18.8% when an average snow depth is about 160 cm and 9.4% at its maximum thickness of 320 cm. The distance between the measurement points at which the spatial covariance of the snow depth disappears falls between 236 and 283 m along the glacier, and between 117 and 165 m across its position. We compared the results of radar measurements of the pulse-delay time of reflections from the base of the snow cover with the data of manual probe measurements at 10 points and direct measurements of snow depth and average density in 12 snow pits. The average speed of radio waves propagation in the snow was determined as Vcr = 23.4±0.2 cm ns−1. This magnitude and the Looyenga and Kovacs formulas allowed estimating the average density of snow cover ρL = 353.1±13.1 kg m−3 and ρK = 337.4±12.9 kg m−3. The difference from average density measured in 12 pits ρav.meas = 387.4±12.9 kg m−3 amounts to −10.8% and −14.8%. In 2014, according to snow and radar measurements, altitudinal gradient of snow accumulation on the glacier Austre Grønfjordbreen was equal to 0.21 m/100 m, which is smaller than the average values (0.35 m/100 m). According to the results of snow measurements of 2011–2014, the average thickness of the snow cover on the glacier Austre Grønfjordbreen was by 17 cm greater than in 1979. In the very snowy year 2012, it was higher by 21.5 cm in comparison with the year 1979, and its spatial variability (standard deviation σН) had increased by 25.6 cm. Estimates of spatial and temporal variability of snow cover depth will be used to analyze the hydrothermal state of the glacier and its changes with regard to revealed features and climatic trends