The Ashikule Volcanic Cluster(AVC), located in the western Kunlun region of the northwestern Tibetan plateau, represents the most recent volcanic activity on Mainland China. This volcanic cluster, which erupted continuously from the Pleistocene to the Holocene, predominantly produced trachyandesites and trachytes, with minor occurrences of phonotephrites, basaltic trachyandesites, and rhyolites. In this study, we present zircon U-Pb-Lu-Hf and whole-rock Sr-Nd-Pb isotopic analyses for volcanic rock samples from AVC. By integrating these data with petrographic, geochronological, and geochemical findings from Yu et al.(2020), we propose further constraints on the petrogenesis of the volcanic rocks and the geodynamic evolution of the western Kunlun region from the Pleistocene to the Holocene.

Zircon U-Pb-Lu-Hf isotopic analyses were conducted on five samples: Two trachyandesitic (515-01 and 518-14), two trachytic (521-1 and 521-4), and one rhyolitic(517-B-03). Together with previous ⁴⁰Ar/³⁹Ar dating, the magmatic zircon grains reveal negative ε_Hf(t) values ranging from -8.8 to -4.4 for the trachyandesitic samples, -8.6 to -5.7 for the trachytic samples, and -9.1 to -6.7 for the rhyolitic sample, suggesting an enriched magma source. The trachyandesitic samples also contain Paleozoic to Mesozoic zircons (165-2 352Ma) with characteristics such as small oval shapes or core-rim structures, indicating that they are inherited zircons. These inherited zircons display ε_Hf(t) values from -3.1 to 9.8, suggesting the involvement of metasedimentary components in the magma source.

Whole-rock Sr-Nd-Pb isotopic analyses were conducted on eight samples(four trachyandesitic, three trachytic, and one rhyolitic), revealing ⁸⁷Sr/⁸⁶Sr ratios of 0.709 395-0.711 441 and ¹⁴³Nd/¹⁴⁴Nd ratios of 0.512 154-0.512 355. In the ¹⁴³Nd/¹⁴⁴Nd-⁸⁷Sr/⁸⁶Sr diagram, these samples plot to the right of the EM Ⅰ region in the fourth quadrant, indicating a relationship with EM Ⅱ-type magmatism. The samples exhibit ²⁰⁷Pb/²⁰⁶Pb ratios of 15.652-15.673 and ²⁰⁶Pb/²⁰⁴Pb ratios of 18.681-18.754, aligning with EM Ⅱ-type and lower crust-derived magmatism on the ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagram.

In the Rb/Nd-Rb diagram, the Ashikule volcanic rocks display an oblique distribution, indicating processes of partial melting or magma mixing, which is further supported by their alignment with the mixing trend on the 1/V-Rb/V diagram. Geochemical modeling results suggest that the Ashikule volcanic magmas formed primarily through a magma mixing process. Previous electron probe microanalysis studies have identified reverse zoning in plagioclase and orthopyroxene phenocrysts, providing additional evidence for magma mixing in the magma chamber. Consequently, these data reveal that Ashikule volcanic magmas originated from a mixing process between EM Ⅱ-type mantle-derived basic magmas and intermediate to acidic magmas from partial melting of ancient continental materials. Considering the tectonic setting of the Tibetan plateau, we propose that Ashikule volcanic activity likely formed in a subduction-dominated environment from the Pleistocene to the Holocene.

The West Kunlun region is located in the northwest margin of the Qinghai-Xizang Plateau. Due to the subduction and collision of the Indian plate, this region has many post-collisional potassic volcanic areas of different sizes. Scholars have conducted many volcanic geology and petro-geochemistry work in the West Kunlun volcanic area, mainly focusing on the origin of deep magmas and plate dynamics. However, the magmatic processes of these potassic volcanic rocks are still unclear. To reveal the magmatic processes in the West Kunlun region and understand the mechanism of volcanic eruption, we analyzed the whole-rock major elements, structure and compositions of the phenocrysts, the crystal size distribution(CSD), and magma crystallization temperature and pressure conditions of the Pulu and Kangxiwa volcanic rocks. The results show that the magma sources of the two volcanic regions are close and their trace element characteristics are similar. Still, their rock types and mineral compositions are significantly different. The Pulu volcanic rocks are mainly trachyandesite and basaltic trachyandesite. The phenocrysts are composed of plagioclase, olivine, clinopyroxene and a small amount of orthopyroxene. The Kangxiwa volcanic rocks are mainly phonotephrite, consisting of clinopyroxene, biotite, and a small amount of olivine and plagioclase. The erosion and zonation of plagioclase, olivine and clinopyroxene were observed under a microscope. There are Nb-Ta and Ti negative anomalies in the two regions, with relative enrichment of large ion lithophile elements(LILF)and light rare earth elements(LREE), indicating that the magma source area has the characteristics of island arc magma, which is related to plate subduction. Based on the analysis of previous Sr-Nd datas, we suggest that the magmas from these two volcanic areas originated from enriched sources.

According to the erosion characteristics, zonal composition data, and the concave CSD pattern, we suggest that the magma in Pulu mixed with acidic magma, whereas the magma in Kangxiwa may only mix with the internal magma, resulting in a large amount of melt erosion of phenocrysts. In Pulu volcanic rocks, the retention time of the smaller size(<5mm)crystal is 190-332a, and that of crystallographic size(>5mm)is 339-860a. The CSD curves of clinopyroxene phenocrysts in Kangxiwa phonotephrites kink at the size of 1.5mm. In Kangxiwa volcanic rocks, the residence time of smaller crystallographic size(<1.5mm)is 5.8-6.4a, and that of larger crystallographic size(>1.5mm)is 9.6-21.2a. The CSD curves of the volcanic rocks from Pulu and Kangxiwa volcanic regions are concave upward, indicating that magma mixing may have occurred both in the two volcanic regions. The An values of the core and the rim of the normal zoning plagioclases and the For value of the normal zoning olivines in the Pulu volcanic rocks vary widely, and the feldspars with low An values at the rim are out of balance with the melt. This indicates that the magma of the Pulu volcanic group mixed with the acidic magma. The Mg# of the normal zoning clinopyroxenes in the Kangxiwa volcanic rocks has a narrow range, and they are all in balance with the melt. The crystallization pressure at the rim was low, and the decompression caused a large number of resorbed phenocrysts to melt. This indicates that the mixing of phenocrysts with different degrees of melting and erosion may result in upward concave CSD curves of clinopyroxenes in the Kangxiwa volcanic rocks, so the Kangxiwa volcanic rocks may only have internal magma mixing.

The mineral-melt equilibrium thermometers show that the equilibrium temperature and pressure of the Pulu volcanic rocks are 1 035-1 218℃, 5.1-9.9kbar, respectively, and the corresponding depth is 19.4~37.3km. The equilibrium temperature of Kangxiwa volcanic rocks is 1 154-1 282℃, the equilibrium pressure is 1.2-11.6kbar, and the corresponding depth is 4.3~43.7km. The variation range of equilibrium pressure in the Kangxiwa region is large, which may be related to the deep fault zone. In this study, by quantitatively studying the magmatic processes of post-collisional potassic volcanic rocks in the West Kunlun region, we provide CSD calculations of the volcanic rocks, reveal the migration and evolution processes of magmas in the crustal magma reservoir, and provide important information for the volcanic activities in the northwest margin of the Qinghai-Xizang Plateau and its surrounding regions.

As one of the largest Quaternary volcanic clusters in China, the volcanic activities of Qiongbei are characterized by multi-stage and multi-cycle. However, the eruption era of Eman volcanic rocks located in the northwest of Qiongbei volcanic cluster is still controversial. In this paper, we present a comprehensive study of volcanic geology and geomorphology, whole-rock major elements, K-Ar geochronology of volcanic rocks and ¹⁴C geochronology of conch, in order to reveal the epoch of volcanic activity and eruption characteristics of Eman volcanic field. According to the field geological survey, it is found that Eman volcanic field has many craters, such as Bijialing, Chunliling, Bingmajiao, Longmenjilang, Longmen Pharos, and Zhangwu. The main types of eruptions are effusive eruption, phreatomagmatic explosive eruption and weakly magmatic explosive eruption. Lava flows almost cover the entire volcanic field, with an area of about 26.3km², which are mainly formed by the eruptions of Bijialing and Chunliling volcanoes in the central-south of the volcanic field. Among them, Bijialing volcano consists of five volcanoes, with steep-slope cones and grayish-black block lavas. Chunliling volcano is located in the east of Bijialing, with gentle slope cone, few lava outcrops and spherical weathering. However, the distribution of base-surge deposits, spattering deposits and scoria is relatively small, and limited to the vicinity of Longmenjilang to Wucaiwan and Zhangwu Village. They were formed by phreatomagmatic explosive eruptions of Bingmajiao and Zhangwu volcano, as well as weakly magmatic explosive eruptions of Longmenjilang and Longmen Pharos volcanoes. Moreover, compared with the Holocene Shishan and Late Pleistocene Daotang basalts in Haikou, Eman volcanic rocks have a wider range of silicon(SiO₂=51.39%~55.00%)and alkali(K₂O+Na₂O=3.51%~8.48%)content. Nevertheless, they are general intermediates, mainly composed of basaltic andesite, basaltic trachyandesite and trachyandesite, and experienced fractional crystallization of olivine and clinopyroxene in the process of magmatic evolution. Combining the weathering degree of volcanic rocks(spherical weathering, red clay layer), volcanic geology and geomorphology(cone morphology, slope), petrology and petrogeochemistry(difference of major elements, olivine phenocryst alteration), K-Ar age of volcanic rocks(0.12~0.44Ma)and ¹⁴C age of conch((43.27±0.67)kaBP), we conclude that the eruption era in Eman volcanic field belongs to the Middle and Late Pleistocene.

Starting from the 1980's of last century, China has launched the national plan of constructing nuclear power plants along the coastline region in eastern China. Currently, in some of these candidate sites, nuclear facilities have been installed and are in operation, but some other nuclear power plants are still under construction or in site evaluation. In 2012 the Atomic Energy Commission issued the specific guide for volcanic hazards in site evaluation for nuclear installations(IAEA Safety Standards Series No. SSG-21), which was prepared under the IAEA's program for safety standards. It supplements and provides recommendations for meeting the requirements for nuclear installations established in the safety requirements publication on site evaluation for nuclear installations in relation to volcanic hazards. To satisfy the safety standards for volcanic hazard, we follow the IAEA SSG-21 guidelines and develop a simple and practical diffusion program in order to evaluate the potential volcanic hazard caused by tephra fallout from the explosive eruptions.
In this practice, we carried out a case study of the active volcanoes in north Hainan Province so as to conduct the probabilistic analysis of the potential volcanic hazard in the surrounding region. The Quaternary volcanism in north Hainan Island, so-called Qiongbei volcanic field is characterized by multi periodic activity, in which the most recent eruption is dated at about 4 000a BP. According to IAEA SSG-21, a capable volcano is one for which both 1)a future eruption or related volcanic event is credible; and 2)such an event has the potential to produce phenomena that may affect a site. Therefore, the Qiongbei volcanic field is capable of producing hazardous phenomena that may reach the potential nuclear power plants around. The input parameters for the simulation of tephra fallout from the future eruption of the Qiongbei volcanic field, such as the size, density and shape of the tephra, the bulk volume and column height, the diffusion parameter P(z), wind direction and intensity, were obtained by field investigation and laboratory analysis. We carried out more than 10000 tephra fallout simulations using a statistical dataset of wind profiles which are obtained from China Meteorological Data Sharing Service System(CMDSSS). Tephra fallout hazard probability maps were constructed for tephra thickness threshold of 1cm. Our results show that the tephra produced by the future large-scale explosive eruption from the Qiongbei volcanic field can affect the area in a range about 250km away from the eruption center.
In summary, the current key technical parameters related to volcanic activity and potential hazards in IAEA/SSG-21 guidelines, such as 10Ma volcanic life cycle and 1×10^-7 volcanic disaster screening probability threshold, etc. are based on the volcanic activity characteristics in the volcanic island arc system. In consideration of the relatively low level of volcanic activity compared with volcanic island arc system due to the different tectonic background of volcanism in mainland China, the time scale of volcanic disaster assessment in IAEA SSG-21 guideline is relatively high for volcanoes in mainland China. We suggest that the study of "conceptual model" of volcanic activity should be strengthened in future work to prove that there is no credible potential for future eruptions, so that these volcanoes should be screened out at early stage instead of further evaluation by probabilistic model.

Tianchi volcano in Changbaishan area is located at the border between China and Democratic People's Republic of Korea, and is one of the most dangerous volcanoes in China. It has experienced several explosive eruptions in late Pleistocene and Holocene, i.e. 50000aBP eruption, 946 AD eruption, 1668 AD eruption, 1702 AD eruption, 1903 AD eruption. Especially, the 946 AD eruption(also known as "Millennium eruption")of this volcano is considered to be one of the largest volcanic eruptions in the world in the past 2000a. The eruption history and strata sequence of Tianchi volcano have long been the focus of attention. The stratigraphic unit division of fallout deposits in the past millennium is controversial, especially for the heterogeneous trachytic pumices(erupted from the Yuanchi stage)above the off-white pumices(erupted from the Chifeng stage).
In this paper, through the detailed field exploration and strata comparation, it was found that there was no depositional interval between the two stage eruptions, or the interval was not long, and thus, it is believed that two stages of fallout pumice should be classified into the Millennium eruption. The off-white fallout pumices in Chifeng stage are relatively homogeneous, with angular shape, normal grading and good sorting. The median size(Md_Φ)and the sorting coefficient(σ_Φ)of Chifeng pumice are in the range of -4.25~-1.3 and 0.93~1.53, respectively. The eruption of Yuanchi stage is in pulsing pattern, and the strata show interbedding of rich khaki pumice layer and rich black pumice layer. The pumices with angular shape show inconspicuous grain grading and good sorting. The median size(Md_Φ)and the sorting coefficient(σ_Φ)of Yuanchi pumice are in the range of -2.55~-0.6 and 1~1.68, respectively. Both the granularities of the pumice particles from two stages are normally distributed and fall into the air-fall field in the median diameter versus sorting diagram. The pumices from 50000aBP and pyroclastic flow of Millennium eruption were also shown in the diagram.
Phenocrysts in pumices are mainly feldspar and pyroxene, but the phenocrysts with obvious resorbed characteristic in Yuanchi black pumice are bigger, and the phenocryst contents are a little higher than those in others. Feldspar content in off-white pumice in Chifeng stage was 0.24%~1.77%, that in khaki pumice in Yuanchi stage was 0.2%~7.5%, and that in black pumice in Yuanchi stage was 3.02%~8.0%. The phenocrysts in Chifeng pumice are broken, which represents more violent explosion. The vesicles inside the pumice also reflect the intensity of the eruption. The Chifeng pumices have large, continuous vesicles and thin vesicle walls. The Yuanchi khaki pumices have continuous vesicles but thicker vesicle wall than the Chifeng pumices. The vesicularity is the lowest and the vesicle walls are the thickest in the black pumices in Yuanchi stage, indicating the eruption strength become weaker from Chifeng stage to Yuanchi stage.
The Chifeng pumices with SiO₂ content of 69.12~72.71wt%, K₂O content of 4.33~4.52wt%, Na₂O content of 5.26~5.39wt%, Al₂O₃ content of 10.32~11.99wt%, CaO content of 0.29~0.95wt%, MgO content of 0.11~0.51wt%, TiO₂ content of 0.23~0.43wt% are comendite in composition. The pumices from 50000aBP eruption are comendite in composition, and their SiO₂ content(65.56~68.28wt%)is slightly lower than Chifeng pumices. The Yuanchi khaki pumices with SiO₂ content of 62.14~63.29wt%, K₂O content of 5.35~5.7wt%, Na₂O content of 5.35~5.62wt%, Al₂O₃ content of 15.00~15.59wt%, CaO content of 1.06~1.61wt%, MgO content of 0.25~0.57wt%, TiO₂ content of 0.4~0.64wt% belong to trachyte in composition, and are close to the composition of the black pumices on the Tianwen Peak. The Yuanchi black pumices are also trachyte in composition, but have obviously lower SiO₂(59.51~60.59wt%), K₂O(4.39~4.84wt%), and Na₂O(4.94~5.08wt%)content, and higher Al₂O₃(15.81~16.42wt%), CaO(2.78~3.66wt%), MgO(1.43~1.9wt%), TiO₂(1.04~1.4wt%)content than the khaki pumices.
The above results show that the eruptive intensity of the Yuanchi stage is weaker than that of the Chifeng stage and the several magmatic compositions of pumices from the Millennium eruption reveal a complex magma system under the Tianchi volcano. The magma layers with different compositions may exist in the magma chamber contemporaneously. At Chifeng stage, only the upper comendite magma erupted, but the magma below erupted in the pulsing pattern at the Yuanchi stage.

The lava flow hazard is an important and frequent disaster for residents in the volcanic area. In this paper, we focus on the lava flow inundation hazard zoning based on the example case of the Ashikule volcano in Xinjiang, China. Firstly, the parameters of magma such as density, viscosity and temperature are calculated by the empirical formula of magma utilizing results of previous field geological survey and petrology analysis. Then, using the kinematic thermo-rheological model, we simulated the inundation area of lava flow from Ashi volcano at the effusion rates of 200m³/s and 500m³/s. The simulation results of Ashi volcano well coincide to the geological map and verify that the method and parameters are valid. Then the applied simulations were carried out to calculate the lava flow inundation area in future eruption at Ashi, Wuluke and Daheishan crater with different effusion rates. At last, according to the analysis of the applied simulation results and drawing lessons from the foreign disaster zoning method, the four-level hazard zoning was built and set with different colors. The first level with red color is the extra-dangerous zone that is always inundated in any eruption but only distributes near the lava spillway of the crater. The second level with orange color is the dangerous zone that is inundated in the medium scale eruption. The third level with yellow color is the sub-dangerous zone that is corresponding to the large eruption. The fourth level with blue color is the potential dangerous zone that is only inundated in the extra-large eruption. In addition, we put forward the suggestion to respond to and avoid the disaster in future. Although China has not been affected by the lava flow for nearly three hundred years, the prospective study in this paper will lay the foundation for the study of related disasters, and provide the reference for the major construction projects in the volcanic area.

Field investigation and lab analysis on samples were carried out for Quaternary volcanoes, including Xiaoshan volcano, Dashan volcano and Bianzhuang hidden volcano, in Haixing area, east of North China. Results show that Xiaoshan volcano with the eruptive material of volcanic scoria, crystal fragments and volcanic ash is a maar volcano, the eruptive pattern is pheatomagmatic eruption, and the influence scope is near the crater. Dashan volcano exploded in the early stage, and then the magma intruded, forming the volcanic neck. The eruption strength and scale are limited, and the eruptive materials are scoria, volcanic agglomerate and dense lava neck. The volcanic rocks in Bianzhuang are porosity and dense volcanic rocks and volcanic breccia, reflecting the pattern of weak explosive eruption and lava flow, and the K-Ar age dating on volcanic rocks indicates that the eruption happened in early Pleistocene. Xiaoshan volcanic scoria and Bianzhuang hidden volcanic rocks are mainly basaltic, Dashan volcanic rocks with lower SiO₂ content are nephelinite in composition. Their oxide contents have no linear relationship, indicating that there is no magma evolution relationship between these magmas from the three places. Three volcanic rocks all have enrichment of light rare earth. The Bianzhuang volcanic rocks are rich in large ion lithophile elements, and have no high field strength elements Zr and Hf, Ti losses. The volcanic materials from Xiaoshan and Dashan are intensively rich in Th, U, Nb and Ta, and significantly poor in K and Ti. Although the magmas from these three places in Haixing area may all come from asthenosphere, the volcanic materials have different petrological and geochemical features, and relatively independent volcanic structures, therefore, they experienced different magma processes.

The mud volcanoes are located in the piedmont downwarp belt of the North Tianshan Mountains in Xinjiang, and all developed at the axis of the anticlinal fold. In this study, based on the geological background and activity of mud volcanoes, we carried out a detailed field investigation on these mud volcanoes at four sites, including Baiyanggou, Aiqigou, Dushanzi and Huoerguosi, and analyzed the particle size, microscopic morphology and composition of the collected samples. The results show that the eruptive types of these mud volcanoes in this area include mud cone, mud shield, mud basin, mud pool and mud hole. The mud liquid surfaces are calm, and bubbling frequency is low. The largest diameter of the nozzle is 2.5m, and the farthest distance of discharged mud flow is about 6.5 meters. The particle sizes of the samples with the similar average sizes are mostly in the range of 0.3～100μm, the medium sizes focus on 5～10μm, and all of the samples are characterized by poor sorting. The column diagrams are generally unimodal distribution and the samples show quite positive skewness in particle size distribution symmetry. The matrix is composed mainly of clay minerals, containing <15% mineral grains mainly of quartz and feldspar, and there are some iron particles in Baiyanggou and Aiqigou samples. According to the analyses, it is proposed that the mud volcanoes in North Tianshan Mountains have the same material source, which is from the middle-lower Jurassic strata, and the high pressure in the strata can be attributed mainly to tectonic activity in the region. At present, the activity of mud volcanoes is relatively weak, and it is unlikely to cause a serious disaster in the near future.

Ashikule Basin is located in the‘arc’intersection of NE-trending Altyn Tagh Fault and NW-trending Kangxiwar Fault, in which there are frequent tectonic activities, and more than 10 volcanoes are developed, including Ashi volcano, the latest active volcano in the Ashikule volcanic group. This paper conducts a detailed study on the Ashi volcano from four aspects, including volcanic geology, lava and phenocryst composition, microstructure features and geothermobarometer. The results show that Ashi volcano consists of volcanic cone and lava flow, and specifically the body of the cone is built by early scoria cone and later spatter cone and the lava flow with the area of about 33km² is divided into four flow units. The lavas belong to shoshonite, trachyandesite in composition, and show porphyritic texture under microscope. The main phenocrysts are plagioclase(major in andesine)and pyroxene(including augite, bronzite and hypersthenes); The matrix is glassy, cryptocrystalline, and phaneritic, part of which has lots of feldspar and pyroxene microlites. The phenocryst-liquid equilibrium temperature is 1 104～1 194℃, and the equilibrium pressure is 570～980MPa, indicating that the depth of the magma chamber is about 18.92～32.29km.

A series of deposits with tens of meters in thickness and in black,grey and yellow colors,from explosive eruptions in the Holocene,are developed at Tianwen peak,the north summit of Tianchi caldera of Changbaishan volcano. Among the deposits,a relatively large scale unit in yellow color,so-called "yellow pumice" by the previous studies,is characterized by coarse tephra and well-developed pores with large-sized trachyte blocks. In this study,we analyzed the petrographic and micro-textural features of the yellow pumice,as well as the grey pumice which is believed to be produced by the millennium eruption in 946 AD.Our results indicate that: 1)the yellow pumice can be classified into alkaline rhyolite as like the grey pumice,but is slightly more basaltic than the grey pumice,suggesting that they all are probably from the identical magma source; 2)remarkably similar as the grey pumice in texture,the yellow deposits are pumiceous with abundant pores in various sizes and few phenocrysts around which moniliform pores are well developed with typical flowing features; 3)parameters of feldspar of the yellow pumice from SEM and X-ray diffraction by predecessors are distinguishable from that of the other pumice,indicating that the yellow pumice is presumably produced by the isolated explosive eruption event. In all,our findings provide strongly petrographic evidences to support the conclusion that the yellow pumice deposits at Tianwen peak of the volcano summit are the product of an explosive eruption prior to the millennium eruption of Changbaishan volcano.

This paper mainly discusses the mud volcano disaster and its genetic mechanism in Ramree Island.Combined with the geological background of Ramree Island and the present situation of the mud volcano,grading analysis and micro-morphology analysis have been made by taking samples from three sampling sites of the northeast,the middle and the western part of Ramree Island.The finding is that the particle sizes of samples between 1～100μm show a unimodel normal distribution,with similar grain size mid-value,concentrated size distribution,poor sorting,and quite positive skewness in grading symmetry; The samples' matrix are mainly argillaceous,containing a lot of argillaceous clasts,tiny crystal clasts and a few pores,and having a little strongly altered plagioclase phenocryst and pyroxene phenocryst,from which,we can judge that the sampling sites have the same provenance.Thus,it can be deduced that there is a uniform argillaceous layer as the unified provenance of the Ramree Island mud volcano.

The shape parameter of particles is an important parameter in the formula of the terminal settling velocity,but it was usually assumed to be spherical or ellipsoidal without detailed study.According to the morphological characterization of the tephra particles erupted during the Millennium eruption of Changbaishan Tianchi volcano,we got some new recognition: The tephra particles consist mainly of pumice,which have irregular shapes,varying from very equant to elongate and from subrounded to angular.With decreasing of the particle size,the elongation of particles becomes significant,and the proportion of elongated particles increases from 15.02％to 47.5％.Moreover,the smaller the size of particles is,the more angular the shape of particles.An average shape parameter F=0.72 has been obtained through the morphological characterization of the pumice particles.The terminal velocity of the pumice particles,which were assumed to be spherical(F=1),erupted during the Millennium eruption of the Changbaishan Tianchi volcano is about 1.52 times the terminal velocity of the pumice particles of F=0.72,and the terminal velocity of the pumice particles,which were assumed to be ellipsoidal(F=0.5), is about 0.89 times the terminal velocity of the pumice particles of F=0.72.When the wind speed is taken to be 10m/s,the isopach map of tephra particles with different shape parameters shows that the dispersal range expands with the decrease of the shape parameter F.The aforementioned results show clearly that the morphology of particles influences strongly both the terminal settling velocity and dispersal range,and hence should be fully considered when simulating tephra dispersion and forecasting disasters in the future.

The pyroclastic deposits from tephra fall,pyroclastic-flow,base-surge,and lahar are well developed in Changbaishan Mountain area where volcanic activity is active in the Holocene.These different pyroclastic deposits are difficult to distinguish from each other in the field because of their similar physical and geological appearance.Through field investigation of pyroclastic deposit sections in the study area,we systematically collected different pyroclastic deposit samples at different sites,and then calculated the grain size parameters and plotted out the probability cumulative curves of all samples in the laboratory.Our results indicate that the pyroclastic samples from different origins can be distinguished by characteristic grain-size diagrams,e.g.median diameter(Md_Ф)versus sorting(σ_Ф),F1 versus F2 diagram.In terms of texture,most pyroclastic deposits show similar characters.However,with the increase of distance from the volcano crater,grain size decreases correspondingly.Finally,Laser Particle Size analyzer is utilized at first time to analyze the subpopulation of fine ash(≤62.5μm)of our samples.On the basis of the fine ash subpopulation histogram distribution and weight cumulative curves,we found that the fine ashes with grain-size from 0.02μm to 62.5μm in pyroclastic-flow deposits and pyroclastic-surge deposits are significantly different due to their different formation origin and different transportation processes.

We have studied the surface features and structural state of the feldspar from the Holocene volcanic eruptive rock on the Tianfeng profile using data from observations under scanning electron microscope and analysis of x ray diffraction.On this profile black pumice appears at the top and darkgrey pumice is present at the bottom.The result shows that the feldspar in these pumice rocks has fresh surface,with slightly weathering for individual cases,and occasionally seen as non-crystalline floc of varied thickness at concaves on its grain surface.This feldspar belongs to the high sandidine-high albite series of the alkali feldspar.The intensity of its characteristic diffraction peak and its plane mesh d value are roughly consistent with the PDF data of anorthoclase.And its constitution((Or37～41,Ab63～59)also implies that it is anorthoclase.It has the following parameters:ordering degree 0.045～0.089,h value-1.010～-1.361,and the lowest crystalline temperature 800～990℃ which is up to 990℃ for the black floc at the top.Our study suggests that the younger volcanic eruption at Tianchi has a lower ordering degree of feldspar and a higher temperature reflected by its structural state.Because the structure of the present feldspar at Tainchi is the result of the cooling process of the hot volcanic rock,the temperature when the feldspar was formed might be very high.The difference of structural state in this feldspar is probably associated with ages and temperatures of volcanic eruptions. The study of its features has some theoretical and applied significance.

A destructive earthquake occurred around Changde,Hunan Province,south-central China in 1631.The previous research of this earthquake yielded 4 different epicenter locations and isoseismal intensity maps.The authors replotted the isoseismals of this event based on checking historical earthquake records,in which the intensity value of the innermost isoseismal is Ⅷ.We concluded that the depth of this earthquake is from 15km to 18km.The basic considerations of our conclusion are as follows:a.This earthquake occurred in an area of lacustrine and fluvial deposits,with the magnitude of M 6¹/2;b.The geometrical center of the innermost isoseismal is the epicenter;c.The depth of epicenter is about 15 to 18km,which is based on the statistical relation between magnitude,depth of the earthquake source and epicenter intensity as well as Xie's statistical result.Finally,the authors discussed the influences of different ground conditions on the textual research and identification of historical data.

The Sihai Tephra Sheet(STS)was formed by the youngest eruption of Longgang volcanic area.The basaltic air fall deposit of this eruption composed the Jinlongdingzi scoria cone and the fallout tephra sheet east of the volcano,near Hongqilinchang in Huinan county and Sihailinchang in Jingyu county.This eruption is considered as Sub-Plinian eruption by using Walker G P L's method.It suggests that the strength of Jinlongdingzi volcano eruption was large.The cumulative frequency plots area shows a good coordination with its concentrated area,as well as a straight right-hand uprising tendency,which indicates a similar sorting process due to gravity during its transportation and setting down.The proximal samples have more coarse grains while the distal part becomes fine-rich as the distance from the vent increased.Although the samples from the other scoria cones are taken from near the vent,the enrichment tendency of the fine material becomes more gentle and have a bigger mass fraction during φ<0,which suggests that the eruption strength of the other volcanoes are obviously smaller than that of the STS.Comparing the distribution feature of the STS with that of Tianchi volcano one can see that the slopes of the Tianchi fallout changes less while the slopes of STS have an obvious variation.The averaged maximum diameter of the STS is smaller than that of Tianchi but the coarse particle proportion of the STS is bigger than that of Tianchi.The up-rise tendency of the fine particles from the STS is not as high as that the samples from the Tianchi volcano,which indicates that the explosivity of the STS is less than that of Tianchi.

Tianchi is a central composite volcano with potential danger of eruption.Tephra of Tianchi eruption in 1215(±15)has diffused to the Japanese sea and southern Japan.However,the study about simulation of the tephra of Tianchi is little.This paper tries to recur to the ash distribution of this eruption by simulating the tephra dispersion of Tianchi volcano eruption.This paper adopts the mathematic model for tephra dispersion proposed by Suzuki(1983).Based on Suzuki's formula,it simulates the tephra dispersion of Tianchi eruption of 1215(±15).There are different densities of the grains from this eruption because of the difference of content of air bubbles.Wind speed and air parameters relate with the altitude.According to the wind speed,we adopt three models:30m/s,MW1 and MW2.The conclusions are as follows:1.The value of the dispersal parameter β of Tianchi eruption in 1215(±15)is 0.45,which indicates most of tephra congregating at the top of the volcano eruption column;2.The differences of settling rates for different diameter particles are very big.For the particles of diameter in 2～1cm,the settling rate achieved 8.95m/s,but for the particles of diameter in 0.005～0.001cm,the settling rate only 0.03m/s;3.There is a turning point in the relations chart of particle diameters and in the settling rate.It is speculated that this turning point possibly relates with transformation of the eruption column from the convective region to the diffusion region;4.The probability densities of diffusion are different for different diameter particles.Big particles start to diffuse at the bottom of the eruption column,but small particles only start to diffuse near the peak of eruption column.And the probability densities of diffusion of small particles are much bigger than that of big ones;5.In the three models the diffusion distance simulated by the first model is farther than that of MW1 model,but the width is smaller.MW2 model is not suitable for this region;6.There is an exponential relationship between the ash deposit thickness and the distance from the volcanic crater in the downwind direction 20km away from the crater.It is nearly 800 years after the eruption.We can only estimate that the downwind is 120°,so in this model it is regardless of the change of the wind direction along with altitude.In addition,there are also some problems about the numerical simulation which need to be solved,for examples,the shape of the volcanic ash particles,the error near the crater,and the second big deposit thickness and etc.

Geometrical parameters of fractures developing in natural rocks, such as density, dominant orientations, length, fracture aperture, are long recognized by engineering scientists because they are not only important parameters to fluid dynamics of fracture systems but also main considering factors for large-scale projects during construction and stability analysis.In this thesis, as a candidate area for high level waste repository (HLW) in China, the rock mass fracture system of the Bantan unit granite of the Jiujing block in the Beishan area, Gansu province, is chosen as the study object. The fracture system is studied in detail by field bedrock outcrop fractures surveying and combining the completed regional geological survey results with acoustic borehole television measurements. Traditional probabilistic statistics and the fractal theory are used to analyze the fracture geometric parameters including fracture length, azimuth and density. Statistics and calculation using the ArcGIS software are made to study fracture distribution characteristics in the granite rock mass. Quantitative description of fracture geometrical parameters is performed in order to provide necessary basic data for the selection of HLW. In the same time, by combining fracture density with fracture network spatial structure and using fractal dimension, the quality of rock mass of the Bantan unit granite is assessed. Fractal dimensions not only describe fracture number of rock mass but also reflect homogeneous degree of fracture distribution and the intact and cracked conditions. So rock mass quality classified by fractal dimensions combined with RQD is more objective and efficient than single RQD index. Above research indicates that the fracture network is characterized by fractal distribution. Fractal dimensions of five sampling sites are in turn 1.636, 1.548, 1.596, 1.724, and 1.604, respectively, and fall into the range between 1.5 and 1.75. According to the rock mass quality classified by fractal dimensions, the Bantan unit granite belongs to rock mass with fracture well developed and normal quality.