scholarly journals Geological methane emissions and wildfire risk in the degraded permafrost area of the Xiao Xing’an Mountains, China

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Wei Shan ◽  
Zhichao Xu ◽  
Ying Guo ◽  
Chengcheng Zhang ◽  
Zhaoguang Hu ◽  
...  
Keyword(s):  
Methane Hydrate ◽  
Methane Concentration ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Methane Emissions ◽  
Permafrost Region ◽  
High Concentration ◽  
Short Term ◽  
Methane Gas ◽  
Marsh Wetland

AbstractWith global warming, the carbon pool in the degradation zone of permafrost around the Arctic will gradually be disturbed and may enter the atmosphere in the form of released methane gas, becoming an important factor of environmental change in permafrost areas. We selected the northwestern section of the Xiao Xing'an Mountains in China as the study area, located in the degradation zone on the southern margin of the permafrost region in Eurasia, and set up multiple study monitoring areas equipped with methane concentration sensors, air temperature sensors, pore water pressure sensors and soil temperature sensors for long-term monitoring of data changes using the high-density electrical method, ground penetrating radar and on-site drilling to survey the distribution of frozen soil and geological conditions in the study area, combined with remote sensing images of Sentinel-2 L1C and unmanned aerial vehicle photographs and three-dimensional image reconstruction, analysis of fire activities and related geological environmental factors. The results show that since 2004, the permafrost thickness of the marsh wetland in the study area has gradually reduced and the degradation rate obviously accelerated; the organic matter and methane hydrate (metastable methane hydrate and stable methane hydrate) stored in the permafrost under the marsh wetland are gradually entering the atmosphere in the form of methane gas. Methane emissions show seasonal changes, and the annual methane emissions can be divided into three main stages, including a high-concentration short-term emission stage (March to May), a higher-concentration long-term stable emission stage (June to August) and a higher-concentration short-term emission stage (September to November); there is a certain correlation between the change in atmospheric methane concentration and the change in atmospheric pressure and pore water pressure. From March to May every year (high-concentration short-term emission stage), with snow melting, the air humidity reaches an annual low value, and the surface methane concentration reaches an annual high value. The high concentration of methane gas entering the surface in this stage is expected to increase the risk of wildfire in the permafrost degradation area in two ways (increasing the regional air temperature and self-combustion), which may be an important factor that leads to a seasonal wildfire frequency difference in the permafrost zone of Northeast China and Southeast Siberia, with the peak in spring and autumn and the monthly maximum in spring. The increase in the frequency of wildfires is projected to further generate positive feedback on climate change by affecting soil microorganisms and soil structure. Southeastern Siberia and northeastern China, which are on the southern boundary of the permafrost region of Eurasia, need to be targeted to establish fire warning and management mechanisms to effectively reduce the risk of wildfires.

scholarly journals Atmospheric Discharge Caused by Methane Emission in Permafrost Degradation Area Caused Wildfire

2021 ◽  
Author(s):  
Wei Shan ◽  
Zhichao Xu ◽  
Ying Guo ◽  
Chengcheng Zhang
Keyword(s):  
Air Temperature ◽  
Electric Potential ◽  
Methane Hydrate ◽  
Discharge Channel ◽  
Methane Concentration ◽  
Negative Charge ◽  
High Concentration ◽  
Near Surface ◽  
Methane Gas ◽  
Positively Charged

Abstract With the development of global warming, the carbon pool in the degraded permafrost zone around the Arctic will gradually be disturbed and enter the atmosphere in the form of methane gas. The frequency and intensity of forest fires will gradually increase, and the release of geological methane will become important factors affecting wildfires in permafrost regions. The northwestern section of China's Xiao Xing'an Mountains, which is located in the degradation zone of the southern edge of the permafrost region of Eurasia, was selected as the research area. Monitoring equipment such as atmospheric electric field, air temperature, methane concentration, soil temperature and pore water pressure were deployed to monitor relevant data changes for a long time. Through indoor soil ventilation tests, it was verified that the friction between gas and soil particles caused the difference in soil electric potential, and the analysis revealed the mechanism of seasonal wildfires in the study area. The results show that the gradual decomposition of metastable methane hydrate and stable methane hydrate stored in the permafrost in the northern part of the Xiao Xing'an Mountains in Northeast China is the main source of high-concentration methane gas entering the atmosphere from the surface. In spring, as the frozen layer on the surface of the study area thaws and the snow gradually melts, the high-concentration, high-pressure methane gas accumulated under the frozen layer will be quickly released into the atmosphere. The study area has the annual maximum value of methane concentration on the surface every spring (March to May), and the rapid rise of gas molecules during the decomposition of underground methane hydrate will cause friction with soil particles, causing methane molecules to be positively charged. Under the action of soil pore pressure and the negative charge at the bottom of the near-surface cloud layer, positively charged methane gas enters the atmosphere. The positively charged methane gas in the air contacts the negative charge in the near-surface cloud layer to form a discharge channel to enhance the discharge phenomenon. With the gradual accumulation of positive charges in the air, the positively charged methane in the air near the ground and the water molecules in the air form positively charged aerosols, and contact with the negative charges near the ground will also form a discharge channel to produce a discharge phenomenon, which will lead to high concentrations of methane gas near the surface were ignited. In addition, the mixed gas with higher pressure and concentration will reduce the thermal spontaneous combustion temperature of methane gas, and when methane aerosol is formed, it will further increase the impact on the air temperature, thereby increasing the risk of wildfires. The electric potential difference between the ground and the near-surface and the flammability of methane aerosols caused by the methane gas emission process in the permafrost degraded area will become an important factor in inducing wildfires.

scholarly journals Short-term velocity variations at three rock glaciers and their relationship with meteorological conditions

2016 ◽  
Vol 4 (1) ◽  
pp. 103-123 ◽  
Author(s):  
V. Wirz ◽  
S. Gruber ◽  
R. S. Purves ◽  
J. Beutel ◽  
I. Gärtner-Roer ◽  
...  
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Surface ◽  
Climatic Conditions ◽  
Water Infiltration ◽  
High Temporal Resolution ◽  
Rock Glacier ◽  
Short Term ◽  
Rock Glaciers ◽  
Velocity Variations

Abstract. In recent years, strong variations in the speed of rock glaciers have been detected, raising questions about their stability under changing climatic conditions. In this study, we present continuous time series of surface velocities over 3 years of six GPS stations located on three rock glaciers in Switzerland. Intra-annual velocity variations are analysed in relation to local meteorological factors, such as precipitation, snow(melt), and air and ground surface temperatures. The main focus of this study lies on the abrupt velocity peaks, which have been detected at two steep and fast-moving rock glacier tongues ( ≥  5 m a−1), and relationships to external meteorological forcing are statistically tested.The continuous measurements with high temporal resolution allowed us to detect short-term velocity peaks, which occur outside cold winter conditions, at these two rock glacier tongues. Our measurements further revealed that all rock glaciers experience clear intra-annual variations in movement in which the timing and the amplitude is reasonably similar in individual years. The seasonal decrease in velocity was typically smooth, starting 1–3 months after the seasonal decrease in temperatures, and was stronger in years with colder temperatures in mid winter. Seasonal acceleration was mostly abrupt and rapid compared to the winter deceleration, always starting during the zero curtain period. We found a statistically significant relationship between the occurrence of short-term velocity peaks and water input from heavy precipitation or snowmelt, while no velocity peak could be attributed solely to high temperatures. The findings of this study further suggest that, in addition to the short-term velocity peaks, the seasonal acceleration is also influenced by water infiltration, causing thermal advection and an increase in pore water pressure. In contrast, the amount of deceleration in winter seems to be mainly controlled by winter temperatures.

scholarly journals Ageing deformation of tailings dams in seasonally frozen soil areas under freeze-thaw cycles

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jiaxu Jin ◽  
Shiwang Li ◽  
Chenguang Song ◽  
Xinlei Zhang ◽  
Xiangfeng Lv
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Frozen Soil ◽  
Practical Significance ◽  
Permafrost Region ◽  
Tailings Dam ◽  
Freeze Thaw ◽  
Tailings Dams ◽  
Thaw Cycle

Abstract The freeze-thaw cycle is one of the important factors in inducing a dam-break in the permafrost region, so it is of great practical significance to study the mechanism of the failure deformation of tailings dams under freeze-thaw cycles. In this paper, the water-heat-force coupling model of a tailings dam considering frost-thaw damage is established, and the freeze-thaw cyclic ageing deformation of a tailings dam in a seasonally frozen soil area is studied. The correctness of the model is validated by numerical calculation. The research shows under the same water content, the compressive strength and modulus of deformation decrease with an increase in the number of freeze-thaw cycles, the cohesion and internal friction angle decrease, and the amplitude gradually decreases before becoming stable. In the process of cooling, the pore water pressure first increases and then decreases, and the pore water pressure first decreases and then increases during the heating process. The research results can provide a theoretical basis and reference values for the stability analysis of tailings dams in seasonally frozen soil areas.

Changes in dielectric permittivity and shear wave velocity during concentration diffusion

1995 ◽  
Vol 32 (4) ◽  
pp. 647-659 ◽  
Author(s):  
J.C. Santamarina ◽  
M. Fam
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Electromagnetic Waves ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
High Concentration ◽  
Interparticle Forces ◽  
Wave Measurements ◽  
Concentration Diffusion

This paper documents a study of concentration diffusion with complementary mechanical and electromagnetic wave measurements. The paper starts with a review of the fundamentals of interparticle forces and wave–geomedia interaction. Experimental data were collected during the diffusion of a high-concentration solution of potassium chloride through different soils with different boundary conditions. Bentonite and kaolinite contracted during diffusion. The interaction between the concentration gradient, true interparticle forces, and fabric changes produced a pore-water pressure front that advanced ahead of the concentration front. The complex permittivity changed with the advance of the concentration front, reflecting the decrease in moisture content and the increase in conductivity. Concentration diffusion affected shear wave propagation through changes in true interparticle forces. Bentonite showed a significant increase in shear wave velocity, whereas the velocity of propagation in kaolinite decreased. Published differences in the behavior of bentonite and kaolinite were compiled and hypotheses are proposed to explain observed phenomena. Key words : mechanical waves, electromagnetic waves, clays, diffusion, double layer.

scholarly journals Investigation and Monitoring of Groundwater Level: Building Crack Near to IIUM Kuantan

2018 ◽  
Vol 5 (3) ◽  
pp. 51-56
Author(s):  
M.F. Ishak ◽  
Koay B.K ◽  
M.S.I. Zaini ◽  
M.F. Zolkepli
Keyword(s):  
Slope Stability ◽  
Pore Water ◽  
Groundwater Level ◽  
Rainfall Intensity ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
High Concentration ◽  
Monitoring Equipment ◽  
Bottom Part ◽  
Level Building

The objective of this study is to analyze groundwater level on slope that effect the slope stability. In this research, the instrumentation monitoring equipment were applied to investigate the groundwater due to the rainfalls that effected to slope stability. Groundwater level were related to rainfall intensity and pore water pressure as the simulation of behavior of the groundwater pattern through slope model were produced. The result indicates that the pore water pressure and groundwater level are facilitated to be fluctuated by heavy rainfall. Moreover, the different part of slopes need to be compared and it was found that the bottom part of the slope has high concentration of groundwater and pore water pressure due to the rainfall cumulative effects. The result also indicates that the bottom slope is worse when it is subjected to a high groundwater level. Thus, the rising of groundwater level due to rainfall was the main reason for the slope resulted in unstable condition.

scholarly journals In situ equilibrium pore-water pressures derived from partial piezoprobe dissipation tests in marine sediments

2013 ◽  
Vol 50 (12) ◽  
pp. 1294-1305 ◽  
Author(s):  
Nabil Sultan ◽  
Sara Lafuerza
Keyword(s):  
Slope Stability ◽  
Pore Pressure ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Design Parameters ◽  
Short Term ◽  
Pore Water Pressures ◽  
Time Required

Excess pore-water pressure has a significant effect on submarine slope stability and sediment deformation, and therefore its in situ equilibrium measurement is crucial in carrying out accurate slope stability assessments and accurately deriving geotechnical design parameters. In situ equilibrium pore-water pressure is usually obtained from pore pressure decay during piezocone tests. However, submarine shelves and slopes are often characterized by the existence of low-permeability (fine-grained) sediments involving long dissipation tests that are an important issue for offshore operational costs. Consequently, short-term and (or) partial dissipation tests are usually performed and in situ equilibrium pore-water pressures are predicted from partial measurements. Using a modified cavity expansion approach, this paper aims to predict for four different sites the in situ equilibrium pore-water pressures. Comparisons between predicted and observed in situ equilibrium pore-water pressures allowed the development of a guide to evaluate the minimum time required to perform short-term dissipation tests for a given marine sediment. The main finding of this Note is that the second derivative of the pore pressure, u, versus the logarithm of time, t, ∂2u/∂ln(t)2 must be positive to calculate accurately the in situ equilibrium pore-water pressures from partial measurements.

scholarly journals Numerical Simulation of Consolidation Characteristics of Diluted Debris Flow

2021 ◽  
Author(s):  
Danyi Shen ◽  
Zhenming Shi ◽  
Hongchao Zheng
Keyword(s):  
Debris Flow ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Reverse Direction ◽  
High Concentration ◽  
Two Phase ◽  
Consolidation Process ◽  
Graded Materials ◽  
Consolidation Settlement ◽  
Graded Material

The consolidation settlement of diluted debris flow is a complicated process of solid-liquid two-phase flow deposition. In this paper, the consolidation and settlement characteristics of uniform-graded and wide-graded debris flow materials in clear water and slurry are simulated by using this method. The results show that in the process of consolidation, sorting occurs in the top and middle position of uniform-graded materials at low concentration, while the middle particles are separated in reverse direction at high concentration. The middle particles of wide-graded material are hardly separated in the whole consolidation process. The velocity of dissipation of excess pore water pressure in the clean water is faster than that of slurry, and the dissipation time of wide-graded materials is longer than that of uniform-graded materials. The research results are helpful to reveal the mechanism of consolidation settlement of diluted debris flow in meso-scale.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

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