Impact of glacier changes and permafrost distribution on debris flows in Badswat and Shishkat catchments,Northern Pakistan

Knowledge of glacier changes and associated hazards is of great importance for the safety consideration of the population and infrastructure in the mountainous regions of Upper Indus Basin(UIB).In this study,we assessed the variations in glacier velocity,glacier surface elevation change,meteorological conditions,and permafrost distribution in Badswat and Shishkat catchments located in UIB to access the potential impact on the occurrence of debris flow in both catchments.We find that the glacier surface velocity increased during the debris flow event in the Badswat catchment and the mean daily temperature was 3.7℃to 3.9℃higher in most of the locations.The enhanced glacier surface elevation lowering period coincide with the rise in temperature during spring and autumn months between 2015 to 2019 in Badswat catchment.The source region of debris flow falls within the lower boundary of permafrost occurrence zone and lies below the 0℃isotherm during late spring and summer months.In Shishkat catchment the 0℃isotherm reaches above the debris flow source area during August and the glacier do not show any significant variations in velocity and surface elevation change.The debris flow source area is adjacent to the slow-moving rock glacier in Shishkat catchment while in Badswat catchment the debris flow initiated from the former glacier moraine.Both catchments are largely glacierized and thus sensitive to changes in climatic conditions and changes in the cryosphere response possess significant threats to the population downstream.Continuous monitoring of cryosphere-climate change in the region can contribute toward the improvement of disaster risk reduction and mitigation policies.

Features of Sandy Debris Flows of the Yanchang Formation in the Ordos Basin and Its Oil and Gas Exploration Significance

Sandy debris flow is a new genetic type of sand bodies,which has gained much attention in recent years and its corresponding theory is proved to be a significant improvement and even partial denial to the 'Bouma Sequence' and 'turbidite fan' deep-water sedimentary theories to some point. Oil exploration researchers are highly concerned with sandy debris flows for its key role in controlling oil and gas accumulation processes.In this article,by applying sandy debris flows theory and combining a lot work of core,outcrop observation and analysis plus seismic profile interpretation,we recognized three types of sedimentary gravity flows that are sandy debris flows,classic turbidites and slumping rocks in chang-6 member of Yanchang Formation in the deep-water area of central Ordos Basin.Among the three types,the sandy debris flows are the most prominent and possesses the best oil bearing conditions.On the contrary,the classic turbidites formed by turbidity currents are limited in distribution;therefore,previous Yanchang Formation deep-water sedimentary studies have exaggerated the importance of turbidite currents deposition.Further study showed that the area distribution of deep water gravity flow sand bodies in Yanchang Formation were controlled by the slope of the deep-water deposits and the flows had vast distribution,huge depth and prevalent advantages for oil forming,which make it one of the most favorable new areas for Ordos Basin prospecting.

Catastrophic Debris Flows on July 10^(th) 2013 along the Min River in Areas Seriously-hit by the Wenchuan Earthquake

Over 240 debris flows occurred in hill-slopes, gullies （ indicated those with single-channel） and watersheds （indicated those with tributaries and channels） on July 10th 2013 in the Wenchuan county, and caused 29 casualties and about 633×10^6 USD losses. This work aimed to analyze characteristics, hazards and causes of these events and explore mitigating measures based on field investigation and remote sensing images interpretation. The debris flows contained clay content of 0.1%~3.56%, having densities of 1.72-2.14 t/m^3, velocities of 5.0-m.7 m/s, discharges of 335-2353 m^3/s and sediment yields of 0.10-1.26×10^6 m^3, and also numerously occurred in large watersheds with the area over lo km^2. Large debris flows formed 3 hazard-chains in slopes, gullies, watersheds and rivers, which all evolved in dammed lakes and outburst flood, and 26 dammed lakes and lO newly ones were generated along the rivers of Min and Yuzi. The remarkable spatial difference of loose solid materials accumulation and intense rainfall, with the cumulative of about or more than 150 mm and the hourly of over 16mm, caused debris flows in the sections from Yingxiu to Miansi and Gengda. The damages on buildings, reconstructions, highways,factories and hydro power station originated from the impacting, scouring, burying of debris flows, the submerging of dammed lake and the scouring of outburst flood, and the huge losses came from the ruinous destructions of control engineering works of debris flows as well as the irrational location and low- resistant capabilities of reconstructions. For hazards mitigating of debris flows in long term, the feasible measures for short term, including risk-reassessing of foregone and potential hazard sites, regional alarming system establishing and integrated control in disastrous sites, and middle-long term, including improving reconstruction standard, rationally disposing river channel bed rise and selecting appropriate reconstruction time and plans, were strongly suggested.

Fractality of grain composition of debris flows

Debris flows in essence are the process of mass transportation controlled by the constitution featured by a wide-ranged distribution of grain size. Debris-flow samples of different densities collected from different regions and gullies reveal that cumulative curve of grain composition, in particular for debris flows of high density, ρ5〉2 g/cm^3, can be fitted well by exponential function with exponents varying with regions and gullies. Debris flows fall into a narrow-valued domain of the exponent, as evidenced by Jiangjiagou Gully （JJG） with high occurrence frequency of debris flows. Furthermore, fractality of grain composition and porosity have been derived from cumulative curves in a certain size range, a range that determines the upper limit of grains constituting the matrix of debris flows. One can conclude that fractal structure of porosity plays crucial roles in soil fluidization that initiates debris flows, and debris flows occur at some range of fractal dimension, in coincidence with field observations.

Debris Flows Risk Analysis and Direct Loss Estimation:the Case Study of Valtellina di Tirano,Italy

andslide risk analysis is one of the primary studies providing essential instructions to the subsequent risk management process. The quantification of tangible and intangible potential losses is a critical step because it provides essential data upon which judgments can be made and policy can be formulated. This study aims at quantifying direct economic losses from debris flows at a medium scale in the study area in Italian Central Alps. Available hazard maps were the main inputs of this study. These maps were overlaid with information concerning elements at risk and their economic value. Then, a combination of both market and construction values was used to obtain estimates of future economic losses. As a result, two direct economic risk maps were prepared together with risk curves, useful to summarize expected monetary damage against the respective hazard probability. Afterwards, a qualitative risk map derived using a risk matrix officially provided by the set of laws issued by the regional government, was prepared. The results delimit areas of high economic as well as strategic importance which might be affected by debris flows in the future. Aside from limitations and inaccuracies inherently included in risk analysis process, identification of high risk areas allows local authorities to focus their attention on the “hot-spots”, where important consequences may arise and local （large） scale analysis needs to be performed with more precise cost-effectiveness ratio. The risk maps can be also used by the local authorities to increase population’s adaptive capacity in the disaster prevention process.

Characteristics, causation, and rehabilitation of Zhouqu extraordinarily serious debris flows in 2010, China

In early morning of Aug 8th, 2010, the rain-triggered tremendous debris flows broke out simultaneously at the Sanyanyu ravine and Luojiayu ravine, which locate in the north part of Zhouqu County town. The debris flow is the most severe event of the same kind of disasters in the past sixty years in China, which caused great losses of people's lives and properties. Based on field investigation, remote sensing image interpretation and analysis of local climatological data, the local topographical conditions, active tectonic movement, massive debris source and torrential rains were the main formation causes which induced the catastrophic debris flows. Moreover, detailed geological surveys were carried out following the disaster, the other geological potential hazard sites were found out, and the geological and seismic hazard assessment has been put into practice. At last, scientific and appropriate countermeasures have been suggested to prevent and mitigate the extraordinarily serious debris flow.

Investigation and Assessment of Landslides and Debris Flows in Sichuan Province of China by Remote Sensing Technique

Taking TM images, ETM images, SPOT images, aerial photos and other remote sensing data as fundamental sources, this research makes a thorough investigation on landslides and debris flows in Sichuan Province, China, using the method of manual interpretation and taking topography maps as references after the processes of terrain correction, spectral matching, and image mosaic. And then, the spatial characteristics of landslides and debris flows in the year of 2005 are assessed and made into figures. The environmental factors which induce landslides and debris flows such as slope, vegetation coverage, lithology, rainfall and so on are obtained by GIS spatial analysis method. Finally, the rela- tionships of landslides or debris flows with some environmental factors are analyzed based on the grade of each envi- ronmental factor. The results indicate: 1) The landslides and debris flows are mainly in the eastern and southern area of Sichuan Province, however, there are few landslides and debris flows in the western particularly the northwestern Si- chuan. 2) The landslides and debris flows of Sichuan Province are mostly located in the regions with small slope degree. The occurring rate of debris flow reduces with the increase of the vegetation coverage degree, but the vegetation cov- erage degree has little to do with the occurrence of landslide. The more rainfall a place has, the easier the landslides and debris flows take place.

Characteristics of Clustering Debris Flows in Wenchuan Earthquake Zone

Clustering debris-flow events, namely many debris flows simultaneously triggered by a regional rainstorm in a large-scale mountainous area,occurred in four regions of Wenchuan earthquake stricken areas in 2008 and 2010. The characteristics of the clustering debris flows are examined with regard to triggering rainfall, formation process, and relationship with the earthquake by field survey and remote sensing interpretation. It is found that the clustering events occurred nearly at the same time with the local peak rainstorms, and the rainfall intensity-duration bottom limit line for clustering debris flows is higher than the worldwide line. It means that more rainfall is needed for the occurrence of the clustering debris flows. Four kinds of major formation processes for these debris flows are summarized: tributary-dominated, mainstreamdominated, transformation from slope failures, and mobilization or liquefaction of landslide. The four regions has a spatial correlation with the strongquake-influenced zone with the peak ground acceleration = 0.2 g and the seismic intensity > X.

Distribution of Debris Flows in Glacier National Park,Montana,U.S.A.

The spectacular scenery of Glacier National Park is the result of glacial erosion as well as post-glacial mass wasting processes. Debris flow magnitude and frequency have been established through extensive fieldwork across seven separate drainage basins in the eastern portion of the park. This paper summarizes the investigation of the hypotheses that debris flow distribution in the Glacier National Park, east of the Continental Divide is （a） not random; and Co） concentrated adjacent to the Continental Divide. The location of 2317 debris flows were identified and mapped from sixty-three 1-m resolution Digital Orthophoto Quarter Quadrangles and their spatial distribution was then analyzed using ArcView Spatial Analyst GIS software. The GIS analysis showed that the debris flows are not randomly distributed nor are they concentrated directly adjacent to the Divide. While the Continental Divide provides orographic enhancement of precipitation directly adjacent to the Divide, the debris flows are not concentrated there due to a lack of available weathered regolith. The most recent Little Ice Age glaciation removed the debris directly adjacent to the Divide, and without an adequate debris supply, these steep slopes experience few debris flows. Both abundant water and an adequate debris supply are necessary to initiate slope failure, resulting in a clustering of debris flows at the break in slope where valley walls contact talus slopes. A variety of summer storm and antecedent moisture conditions initiate slope failures in the Glacier National Park, with no distinct meteorological threshold. With over two million visitorsevery year, and millions of dollars of park infrastructure at risk, identifying the hazard of debris flows is essential to future park management plans.

Classification and Facies Sequence Model of Subaqueous Debris Flows

Objective Debris flows are cohesive sediment gravity flows which occur in both subaerial and subaqueous settings. Compared to subaerial debris flows which have been well studied as a geological hazard, subaqueous debris flows showing complicated sediment composition and sedimentary processes were poorly understood. The main objective of this work is to establish a classification scheme and facies sequence models of subaqueous debris flows for well understanding their sedimentary processes and depositional characteristics.

Comparison of the entrainment rate of debris flows in distinctive triggering conditions

Debris flows can be extremely destructive because they can increase in magnitude via progressive entrainment. In this paper, a total of 18landslide-type debris flows and 268 channelized debris flows in Wenchuan earthquake and Taiwan region, as well as other regions were collected to analyze the entrainment rate of debris flows in each triggering condition. Results show that there is a power relationship between volume of initial triggered mass and final deposited debris for landslide type debris flow. The debris flows during2008 and 2013 in Wenchuan earthquake-region have smaller entrainment rate than that from 2001 t02009 in Taiwan. The entrainment rate of debris flow events from 2001 to 2009 in Taiwan shows a decaying tendency as elapsed time. Comparison of the entrainment rate in the two earthquake-hit regions with other regions proves that entrainment rate has a close relation with major sediment availability and secondary rainstorm conditions.

Debris flow simulation 2D(DFS 2D):Numerical modelling of debris flows and calibration of friction parameters

Debris flows are rapid mass movements with a mixture of rock,soil and water.High-intensity rainfall events have triggered multiple debris flows around the globe,making it an important concern from the disaster management perspective.This study presents a numerical model called debris flow simulation 2D(DFS 2D)and applicability of the proposed model is investigated through the values of the model parameters used for the reproduction of an occurred debris flow at Yindongzi gully in China on 13 August 2010.The model can be used to simulate debris flows using three different rheologies and has a userfriendly interface for providing the inputs.Using DFS 2D,flow parameters can be estimated with respect to space and time.The values of the flow resistance parameters of model,dry-Coulomb and turbulent friction,were calibrated through the back analysis and the values obtained are 0.1 and 1000 m/s^(2),respectively.Two new methods of calibration are proposed in this study,considering the crosssectional area of flow and topographical changes induced by the debris flow.The proposed methods of calibration provide an effective solution to the cumulative errors induced by coarse-resolution digital elevation models(DEMs)in numerical modelling of debris flows.The statistical indices such as Willmott's index of agreement,mean-absolute-error,and normalized-root-mean-square-error of the calibrated model are 0.5,1.02 and 1.44,respectively.The comparison between simulated and observed values of topographic changes indicates that DFS 2D provides satisfactory results and can be used for dynamic modelling of debris flows.

ANALYSIS OF METEOROLOGICAL CONDITION AND RESEARCH ON FORECAST OF LANDSLIDES AND DEBRIS FLOWS IN ZHEJIANG PROVINCE

1 INTRODUCTION Meteorological factors, especially precipitation, have close links with geological calamities. According to the statistics, more than 70% of the geological calamities in China occur in rainy seasons. Many researchers are thus motivated to study extensively to determine their relationship in the prediction of geological calamltles . They either rely on single measurements of rainfall to seek basis for widespread occurrence of geological calamities or treat antecedent diurnal rainfall with equal importance, though with account of the accumulated effect of preceding rainfall. Furthermore, it is common for quite a number of models to use the rainfall recorded at hydrological or meteorological rain gauges as the one for the interested day, reducing the time validity of the prediction. In our analysis, it is found that the landslides and debris flows in Zhejiang province are related with the antecedent precipitation （but not by a simple accumulation）. Critical amounts of accumulated and effective rainfall are used in this work to tell whether there will be geological calamities. Moreover, MM5 is used to forecast rainfall, taking account in equations of the predictand for landslides and debris flows, in attempts to predict the appearance of meteorological condition for geological calamities and improve the rationality of forecasting procedures and time validity of forecasts.

Geomorphologic analysis and physico-dynamic characteristics of Zhatai-Gully debris flows in SW China

Zhatai gully is a typical debris flow channel in Butuo county of Sichuan province, southwestern China. The geomorphologic features are analyzed and the physical-dynamic characteristics are discussed on the basis of field investigation and laboratory tests. Geomorphologic analysis indicates that Zhatai-gully drainage in relation to debris flow can be divided into source area, transport area, and deposition area. The source area has a steep slope and has very limited vegetation cover, which favors runoff, allowing loose solid materials to be mobilized easily and rapidly. In the transport area, there are many small landslides, lateral lobes, and loose materials distributed on both banks. These landslides are active and constantly providing abundant source of soils for the debris flows. In the deposition area, three old debris-flow deposits of different ages can be observed. The dynamic calculation shows that within the recurrence intervals of 50 and lOO years, debris flow discharges are 155.77m^3/s and 178.19m^3/s and deposition volumes are 16.39 × 10^4 m^3 and 18.14 × 10^4 m^3, respectively. The depositional fan of an old debris flow in the outlet of the gully can be subdivided into six layers. There are three debris flow deposits on left and two on the right side of the gully. Grain-size tests of sediments from the soil, gulley bed deposits, and the fresh and old debris flow deposits showed that high amounts of clay and fine gravel were derived from the soil in the source area whereas much of the gravel fraction were sourced from the gully bed deposits. Comprehensive analysis indicates that Zhatai gully is viscous debris-flow gully with moderate to high frequency and moderate to large magnitude debris flows. The risk of a debris flow disaster in Zhatai-gully is moderate and poses a potential threat to the planned hydroelectric dam. Appropriate engineering measures are suggested in the construction and protection of the planned hydroelectric station.

Experimental analysis for the dynamic initiation mechanism of debris flows

Debris flow is one of the major secondary mountain hazards following the earthquake. This study explores the dynamic initiation mechanism of debris flows based on the strength reduction of soils through static and dynamic triaxial tests. A series of static and dynamic triaxial tests were conducted on samples in the lab. The samples were prepared according to different grain size distribution, degree of saturation and earthquake magnitudes. The relations of dynamic shear strength, degree of saturation, and number of cycles are summarized through analyzing experimental results. The findings show that the gravelly soil with a wide and continuous gradation has a critical degree of saturation of approximately 87%, above which debris flows will be triggered by rainfall, while the debris flow will be triggered at a critical degree of saturation of about 73% under the effect of rainfall and earthquake(M>6.5). Debris flow initiation is developed in the humidification process, and the earthquake provides energy for triggering debris flows. Debris flows are more likely to be triggered at the relatively low saturation under dynamic loading than under static loading. The resistance of debris flow triggering relies more on internal frication angle than soil cohesion under the effect of rainfall and earthquake. The conclusions provide an experimental analysis method for dynamic initiation mechanism of debris flows.

Characteristics and Causes of Disastrous Debris Flows on July 4, 2013, in Shimian County, Sichuan, China

Debris flow is an abrupt phenomenon of earth surface movement and typical disaster in mountainous areas with steep terrace, quantity of loose soil and abundant surface runoff. Intense rainfall and rainstorm easily triggered debris flows and generated huge losses. The disastrous debris flows, on July 4, 2013 at the gullies of Hou, Heilinzi and Xiongjia in Shimian County, Sichuan Province, resulted in 18 casualties and endangering Shimian city with a population of 50,000. These debris flows were characterized by low viscosity with only 0.9% - 1.4% clay soil of less than 0.05mm, density of 1.77 - 1.84 t/m3, velocity of 4.4 - 13.5m/s and discharge of 827 - 1248 m3/s, respectively, and also delivered sediment of 16.8 × 104m3, 12.7 - 13.5 × 104 m3, 20.5 × 104m3 out of the outlet, respectively. These three events all generated a hazard chain, which involved in flash flood, channelized debris flow, dammed lake and outburst flood. The threshold conditions of debris flow blocking Nanya River and forming this hazard chain are that the unit width peak discharge and the deposition volume in river channel are more than 37.0 m3/s and 4500 m3, respectively. These debris flows were initiated by intense rainfall with the antecedent rainfall of over 52 mm and triggering rainstorm of over 36 mm/h. And, the property losses and casualties mainly originated from impacting and scouring, burying and blocking, highway destructing and river channel rising. The irrational location of constructions and the destruction of under-standard prevention constructions were responsible for loss worsening. It was strongly recommended for mitigating that hazards reassessment, integrated control, emergency plan and integrated risk management were made at mountainous urban areas, especially in high-hazard areas.

The Critical Rainfall Characteristics for Torrents and Debris Flows in the Wenchuan Earthquake Stricken Area

Critical rainfall assessment is a very important tool for hazard management of torrents and debris flows in mountainous areas. The Wenchuan Earthquake 2008 caused huge casualties and property damages in the earthquake-stricken area,which also generated large quantities of loose solid materials and increased occurrence probabilities of debris flows. There is an urgent need to quantify the critical rainfall distribution in the area so that better hazard management could be planned and if real time rainfall forecast is available,torrent and debris flow early-warning could be issued in advance. This study is based on 49-year observations (1954-2003) of up to 678 torrent and debris flow events. Detailed contour maps of 1 hour and 24 hour critical rainfalls have been generated (Due to the data limitation,there was insufficient 10 minute critical rainfall to make its contour map). Generally,the contour maps from 1 hour and 24 hours have similar patterns. Three zones with low,medium and high critical rainfalls have been identified. The characteristics of the critical rainfall zones are linked with the local vegetation cover and land forms. Further studies and observations are needed to validate the finding and improve the contour maps.

Risk Assessment of Highways Affected by Debris Flows in Wenchuan Earthquake Area

Since the Wenchuan earthquake in China on May 12th, 2008, highways in earthquake-affected areas have been frequently interrupted by debris flows. We analyzed the hazard effect modes and damage processes along highways and developed three key indexes, scale of debris flows, deposits on highways and river blockage, to describe quantitatively the highway disasters. By combining the empirical methods and the actual terrain conditions, we proposed new methods to determine the value of hazard indexes. In addition, we used the economic value and resistance of highway as vulnerability assessment indexes, then determined the specific subindexes for the subgrade, bridges and culverts, and developed a way for the quantified vulnerability zoning. Moreover, we proposed the assessment and mapping methods for highway risk. The risk is described into 5 grades： extremely low risk, low risk, middle risk, high risk and extremely high risk. We applied these methods in a case study carried out on provincial highway S3o3 from Yingxiu Town to Wolong Town, in Wenchuan County. Analysis of debris flow risk for the whole highway, showed that the total length of highway in extremely low risk area was 28.26 km, 4.83 km in low risk area, 8.0 km in middle risk area, 3.65 km in high risk area, and 3.06 km in extremely high risk area. The assessment results are consistent with the field survey data which reflected the disaster situation. This risk method can be used objectively to evaluate the debris-flow risk along highways, and is useful for highway reconstruction in mountainous areas suffering from active debris flows.

Combined Impacts of Antecedent Earthquakes and Droughts on Disastrous Debris Flows

This paper describes a study on the combined impacts of antecedent earthquakes and droughts on disastrous debris flows.This is a novel attempt in quantifying such impacts using the effective peak acceleration(EPA)(to represent earthquakes) and standardized precipitation index(SPI)(to represent droughts).The study is based on the analysis of 116 disastrous debris flow events occurred in China's Mainland in the last 100 years covering a wide spectrum of climate types and landforms.It has been found that the combined impacts from earthquakes and droughts on disastrous debris flows do exist and vary from low to very high according to different climate conditions and terrains.The impacts from earthquakes increase with the increased terrain relief,and the impacts from droughts are strongest in semi-humid climate condition(with reduced impacts in humid and semi-arid /arid climate conditions).Hypothetical explanations on the study discoveries have been proposed.This study reveals the possible reasons for the disastrous debris flow distributions around the world and has significant implications in paleo-climate-seismicanalysis and disastrous debris flow risk management.

Slope Debris Flows in the Wenchuan Earthquake Area

Avalanches and landslides,induced by the Wenchuan Earthquake on May 12,2008,resulted in a lot of disaggregated,solid material on slopes that could be readily mobilized as source material for debris flows.Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years.Slope debris flows(as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks.Based on field investigations and measurements of 19 slope debris flows,their main characteristics and potential mitigation strategies were studied.High rainfall intensity is the main triggering factor.Critical rainfall intensities for simultaneous occurrence of single,several and numerous slope debris flow events were 20 mm/day,30mm/day,and 90 mm/day,respectively.Field investigations also revealed that slope debris flows consist of high concentrations of cobbles,boulders and gravel.They are two-phase debris flows.The liquid phase plays the role of lubrication instead of transporting medium.Solid particles collide with each other and consume a lot of energy.The velocities of slope debris flows are very low,and their transport distances are only several tens of meters.Slope debris flows may be controlled by construction of drainage systems and by reforestation.