Study of Distal Pyroclastic-flow Stratum from Tianchi Volcano in 1215(±15) Eruption:Pyroclastic-flow Over Water

In this paper, we describe three strata at the distal part of the pyroclastic-flow from the Tianchi volcano in 1215 （±15） eruption. One of the strata with crosslayers that are different from typical pyroclastic-flow strata may come from a ground-surge. The grain-size and scanning electron microscopy （SEM） analysis was performed to study the origin of the pyroclastic-flow. Characteristics of grain-size distribution show that it is similar with the ash cloud. Through the SEM analyses, we found some quench structures with less damage on the surfaces of the vitric pumices. These phenomena indicate that there has been hydration in the transportation processes at the distal of pyroclastic-flow. It has partly changed the transportation mechanism of pyroclastic-flow, which transitions form dense flow to diluted flow. This paper develops a new distal pyroclastic-flow model in the Tianchi volcano that can be divided into three stages, i.e. the quench stage, expanding stage and depositing stage.

Recent Geochemical Variation of the Hot-Spring Gases from the Tianchi Volcano, Changbai Mountains, Northeast China

Recent fluid monitoring work shows that the contents of mantle-derived CO2, He and CH4 increased anomalously in 2002 and 2003. The ^3He/^4He ratio of the deep-fault-type Jinjiang hot springs increased highly anomalously in 2003, and then decreased in 2004. The ^3He/^4He ratio from the thermal-reservoir-type Changbaijulong hot springs increased slowly in 2003, and the increase continued in 2004. The mantle-derived He content of the He released from the Changbaijulong springs increased obviously in 2004. The anomaly of the released gases and the isotopic He was consistent with the trends of seismic activities in the Tianchi volcanic area between 2002 and 2004. The abnormal release of the Jinjiang hot springs apparently decreased after the seismic activities ceased in the second half of 2004, while the abnormal release from the Changbaljulong increased significantly after these seismic activities. It shows that the abnormal release of magmas-derived gases from the thermal-reservoir-type springs lags behind that of the deep-fault-type springs. These characteristics may be of great significance for identifying deep magmatic activity and predicting volcanic earthquakes in the future.

Heating Stage Experimental Study of Melt Inclusions in Feldspars from Three Holocene Eruptions of Changbaishan Tianchi Volcano

There occurred several eruptions from Changbaishan Tianchi volcano in Holocene, and at least three of them were believed to be true according to the formal studies. The products of three eruptions were yellow comenditic pumice of - 5000a B.P. （Eruption Ⅰ ）, gray comenditic pumice and pyroclastic flow of - 1000a B.P. （ Eruption II, i.e. the millennium explosive eruption）, black trachy pumice and welded tuff of - 300a B.P. （ Eruption Ⅲ ） respectively. There were a large number of melt inclusions found in phenocrysts, which differ in size and color. The Leitz 1350 heating stage experiments for melt inclusions in host feldspars from three Holocene eruptions of Changbaishan Tianchi volcano imply that there were little differences between the homogenization temperatures of melt inclusions from Eruptions Ⅰ and Ⅲ, whereas it was rather complicated for Eruption H, i.e. there might be two kinds of melt with different homogenization temperature periods, which gave the evidence for the assumption that the explosive millennium eruption of Tianchi volcano was triggered by injection and mixing of two different magmas. The experimental results also indicate that （ 1 ） small melt inclusion is easy to be homogenized, while the large one, especially the one with lots of daughter crystals, is rather difficult to be homogenized; （2） homogenization temperature closely correlates with the size of melt inclusion within host crystal, with the temperature point switching from high heating rate to low heating rate, and correlates with whether it is the first time to obtain homogenization as well; and （3） a melt inclusion can get different homogenization temperatures when it is repeatedly heated. Even more, the next homogenization temperature is usually higher than the former one, which testifies the phenomenon that hydrogen migration occurs during repeated heating.

Progresses in geology and hazards analysis of Tianchi Volcano

A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temperature feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption.

Elementary analysis of data from Tianchi Volcano

Tianchi Volcano is the largest potential erupticve volcano in China. Analyzing these data on seismic monitoring, deformation observation and water chemistry investigation gained from the Tianchi Volcano Observatory(TVO), the authors consider that the Tianchi Volcano is in going into a new flourishing time.

Geochemical Features of the Hubin Spring Gases from the Northern Caldera Lake of the Tianchi Volcano,Changbai Mountains

This paper deals with geochemical features of gas emitted from the Hubin Springs. The Hubin Springs zone, a strong thermal emission zone, is are locatedd at the north edge of the Tianchi caldera lake. Very young deposits with uncertain eruption date are found on the top area of the Tianwenfeng, which might have been formed in one of the recent eruptions or the Millennium Eruption. It is of significance to study the geochemistry features of the emitting gas from the Hubin Springs to understand the activities of the Tianchi Volcano. This paper systematically sampled and analyzed the gases emitted from the Hubin Springs and discussed their geochemistry features. The results show that there is a high content of deep derived gases, such as CO2, He, CH4 and Ar in Hubin Springs zone. The isotopic ratio of He lies between 4. 18 and 5. 95 Ra. The averaged mantle derived gas content calculated from the ^4He/2^20Ne ratio and He content reaches 67.1%. All these show that the Hubin Springs are located on a special belt of deep gases released in high intensity and large scale. The spatial distribution of Helium isotope is characterized by concavity, showing that this special area may be related to the volcanic edifice. It is highly possible that the released gases represent the residual gas samples of the latest eruptions from the Tianchi Volcano. However more detailed studies are demanded.

The Activity of Major Faults and the Hydrothermal Alteration Zone at Tianchi Volcano of Changbaishan

It is found by field investigation that the near horizontal top surface of the brown or brick-red hydrothermal alteration zone varies obviously in elevation at different sections of the same layer on the caldera’s inner wall of Tianchi, with that at the north section near the Tianwen Peak about 110 m higher than that at the south near the Jiangjun Peak in Korea. The top surface of the hydrothermal alteration zone can be taken as key horizon to tectonic movement. The difference indicates that the total uplift height of the NW wall of the Liudaogou-Tianchi-Jingfengshan fault, the principal fault trending NE at Tianchi, is bigger than that of the SE wall ever since the occurrence of hydrothermal alteration. This also explains why the topography in the northwest side of Tianchi is steeper and with more developed river system than in the southeast. The uplifting of the northeastern wall is bigger than that of the southwest along the principal NW-trend fault, namely, the Baishanzhen-Tianchi-Jince fault. It is observed from characters of hydrothermal alteration and the palaeoresiduum, that the recent vertical movement rate along the principal NE-trend fault is larger than that of the principal NW-trend fault. The two faults intersect at Tianchi, dividing the volcano into 4 blocks, with the uplift magnitudes decreasing successively in the order of the north, the west, the east and the south block. The biggest uplift of the north block corresponds well to the shallow magma batch in the north of Tianchi observed by DSS and telluric electromagnetic sounding, and etc. and they may be related with the causes.

Characteristics of S-wave Envelope Broadening in the Changbaishan Tianchi Volcano

High-frequency S-wave seismogram envelopes of microearthquakes broaden with increasing travel distance,a phenomenon known as S-wave envelope broadening. Multiple forward scattering and diffraction for the random inhomogeneities along the seismic ray path are the main causes of S-wave envelope broadening,so the phenomenon of S-wave envelope broadening is used to study the inhomogeneity of the medium. The peak delay time of an S-wave,which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope,is accepted to quantify S-wave envelope broadening. 204 small earthquake records in Changbaishan Tianchi volcano were analyzed by the S-wave envelope broadening algorithm. The results show that S-wave envelope broadening in the Changbaishan Tianchi volcano is obvious,and that the peak delay time of S-wave has a positive correlation with the hypocenter distance and frequency of the S-wave. The relationships between the S-wave peak delay time and the hypocenter distance for different frequency bands were obtained using the statistics method. The results are beneficial to the understanding of the S-wave envelope broadening phenomena and the quantitative research on the inhomogeneities of the crust medium in the Changbaishan Tianchi volcano region.

Transporting and Deposition Dynamics in the Plinian Column of Tianchi Volcano,Changbaishan

The huge comendite ignimbrite-forming eruption of Tianchi Volcano maintained a stable plinian column during its earlier stage of eruption, and succeeded a collapsing of the column producing pumiceous ignimbrite deposits. It is estimated that the column height (Hb) varied from 20km to 10km in its eruption period, with a maximum height of 25km in the eruption peak. Its umbrella cloud spread into the stratosphere with a top height of 35km (Ht). The dense lithics whose diameter exceeded 8cm followed a ballistics trajectory in a 3km-high gas thrust region, while the smaller lithics and pumices entered the convection region in the column. The initial magma temperature was 780℃. The comendite magma had an exit velocity of 300m/s, volatile content of about 1wt% and lithics of 8.5wt%. From a 400m-wide vent the magma was expelled out with a mass eruption rate of 108.36kg/s, corresponding to a volume rate of 104.95m 3/s. Over 1.3436×10 19 J of energy had been released from Tianchi Volcano, of which the kinetic proportion was about 8%. The plume had a temperature of -50℃ at the base focus of the cloud and a upward speed of 215m/s. The cloud spread out at a gradually downspeed with the increasement of distance from its center. For example, at a distance of 25km from its center the spreading velocity is about 250m/s, and is about 60m/s at distance of 100km. The main part of the plinian column, that is the convection region, once occurred in the height between 3 to 25km, and its maximum width was about 13km in radius.

Effect of gas emissions from Tianchi volcano (NE China) on environment and its potential volcanic hazards

The Tianchi volcano in the Changbai Mountains is located on the boundary between China and North Korea.There are many times of eruptions of the Tianchi volcano during the Holocene.One of its large eruptions occurred around 1000 years ago dated by ^(14)C method and historical records.Composition of products of the largest Tianchi volcanic eruption studied is characterized by comendi-tic Plinian fallout and unwelded ignimbrite,which are mainly distributed in China and North Korea.Caldera is about 4.4 km long and 3.4 km wide,which had filled with water(e.g.Tianchi Lake).The Tianchi volcanic cone is about 2700 m high above sea level.The Tianchi Lake is located on the summit of the volcanic cone,that is also highest peak of the Changbai Mountains in northeastern China.This study analyzed Cl,F,S and H_(2)O concentrations of melt inclusions in the phenocryst min-erals(anorthoclase and quartz)and co-existing matrix glasses using the electron microprobe and estimated environmental effect of Tianchi volcanic gases.The authors proposed a new method to evaluate future eruption of active volcano and estimate potential volcanic hazards based on contents of volatile emissions.Using this method,we made a perspective of future volcanic hazard in this region.

CLIMATE EFFECT OF THE LAST LARGE ERUPTION OF TIANCHI VOLCANO

Volcanic eruption is an important external forcing factor of climate change on time scale from month to hundred years.In this paper,the climatic effect of the last large historical eruption of Tianchi volcano,which happened in 1229 AD,has been investigated with a two-dimensional energy balance model.Taking Mt.Pinatubo volcano and Changbai Mountain-Tianchi volcano for example,the numerical simulation on time scale from months to years indicates that such large eruptions may have significant impacts on global climate.Based on the simulation results,it is suggested that the last large eruption of Tianchi volcano should be responsible for the abrupt climate change event,which began in the period from 1230 to 1260 AD.

The magma evolution of Tianchi volcano, Changbaishan

The Changbaishan Tianchi volcano is composed of the basaltic rocks at the shield-forming stage, the trachyte and pantellerite at the cone-forming stage and modern eruption. Studies on their REE, incompatible elements and Sr, Nd, Pb isotopes suggest that rocks at different stages have a common magma genesis and close evolution relationship with differentiation crystallization playing the key role. The co-eruption of basaltic trachyandesite magma and pantellerite magma indicates that there exist both crustal magma chamber and mantle magma reservoir beneath the Tianchi volcano.

Application of satellite thermal infrared remote sensing in monitoring magmatic activity of Changbaishan Tianchi volcano

In this paper, with the application of satellite thermal infrared remote sensing technique, nine land surface temperature distribution maps of Changbaishan Tianchi volcano area are retrieved from nine thermal infrared images which are taken from 1999 to 2008. In terms of NDVI (Normalized Difference Vegetation Index), we classify the surface cover of the study area into three types, i.e. vegetation (forest), mixture of soil and vegetation (short grasses), and bare rock. The average temperature of each type of surface covers is calculated first, and then the average daily temperature record from Tianchi meteorological station is subtracted in order to reduce the effect of weather variation. Finally, thermal anomalies of three types of surface cover in Changbaishan Tianchi vol-cano area in the period of 1999 to 2008 are obtained, which is believed to reflect the magmatic activity in the magma chamber under Tianchi volcano caldera. Our results indicate that temperature of the study area increased with an intermittent tendency during 1999 to 2005, but dropped after 2005, and then maintained a relatively stable state from 2006 to 2008. Such a tendency of annual temperature variation possibly caused by magmatic activity is correlated with the results observed by means of seismic monitoring, ground deformation from GPS measurement, and volcanic gas geochemistry monitoring in the same area. It is im-plied that the upward intrusion of magma may cause temperature increase, and such temperature variation is great enough so that could be detected by using satellite thermal infrared remote sensing technology.

长白山天池火山含碳气体排放特征

查明火山气体释放的规模及空间分布特征,对火山监测与喷发预测、评估地质源温室气体释放及气候环境变化等具有重要意义。本文采用密闭气室法观测土壤气浓度,计算了长白山天池火山区CO_(2)和CH_(4)气体释放通量,结合高光谱气体CO和CO_(2)分析了火山区不同区域气体释放特征及影响因素。结果表明:(1)长白山天池火山区土壤CO_(2)通量范围为0.16~1051.39 g·m^(-2)·d^(-1);CH_4通量值范围为-0.05~4.68 g·m^(-2)·d^(-1)。长白山天池火山区气体释放在空间上呈环带状分布特征,火山口周缘气体释放较弱,在聚龙温泉群、锦江温泉群和锥体海拔1800~2200 m范围内气体释放最为强烈。(2)长白山天池火山含碳气体释放在地表和高光谱卫星观测的时间和空间上都有一定的相关性,火山口上方气体释放最弱。(3)长白山天池火山含碳气体排放的空间差异可能受到火山口特殊条件、断裂构造、温泉地热储和岩浆作用的控制。

Potential Hazards of Eruptions around the Tianchi Caldera Lake, China

Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding downstream.

长白山天池火山晚更新世以来岩浆房系统的压力探讨

长白山天池火山是一座大型的复合式活火山,由于其曾剧烈的喷发活动(946~947AD)和2002-2006年的扰动事件而备受瞩目。自晚更新世以来,天池火山有过多次剧烈的爆炸式喷发活动,其岩浆主要为高分异的碱流质与粗面质岩浆,SiO_(2)>65%。地球物理探测表明天池火山地下在浅部地壳存在岩浆房,但却未能对历史喷发活动的岩浆系统进行约束。本文利用晚更新世以来喷发物的电子探针数据,运用Qz-Ab-Or系统投图、单斜辉石机器学习压力计以及rhyolite-MELTS压力计对各期喷发的岩浆驻存压力条件进行计算,认为天文峰期(TWF)碱流岩压力约246~444MPa、气象站期(QXZ)碱流岩压力约184~344MPa、千年大喷发(ME-I)碱流岩压力约162~314MPa,千年大喷发(ME-II)粗面岩压力约438~540MPa。通过压力与深度换算后发现上述喷发岩浆贮存位置均对应中上地壳深度的岩浆房,并且三期碱流岩压力随喷发时间逐渐降低,暗示天池碱流质岩浆房在万年尺度内逐渐向浅部地壳演化的趋势;而粗面质岩浆可能来自另一个更深的岩浆房。该发现将有助于提高对天池火山岩浆房系统演化的认识,并为火山监测数据解释和灾害预警等工作提供依据。

长白山天池火山地热系统——岩浆囊与隐伏高温地热资源

长白山天池火山是晚新生代中心喷发式复合型层状火山,全新世以来发生过多次大规模喷发,与深部岩浆热扰动活动相关的构造地震、地表形变、温泉气体组份等均显示该火山仍可能再次喷发,是我国东部潜在的高温地热资源区。长白山天池火山周边地下水十分丰富,具有形成高温水热活动的岩浆囊热源。为探索地壳浅层隐伏的高温地热资源,本文在野外考察基础上,利用地热学方法,计算了该区地层结构与热状态,分析了地表下的火山地热系统。结果表明:长白山天池火山区地下2 km深处的温度在66—110℃之间,12 km深处的温度在313—417℃之间;该区居里面深度较浅,平均深度为12.7 km,居里点温度为375℃,其中长白山天池火山喷发中心和望天鹅火山喷发中心为居里面上隆区;在人工地震基底速度约束下,通过沉积地层重力反演发现,在约3.5—5.5 km深度处存在密度梯级高压带,该高压带与12 km深度处的岩浆囊之间的区域是形成隐伏高温地热资源的有利区域。

Study on shallow structural features in Changbaishan Tianchi volcanic region

A seismic survey by 10 shallow profiles and 6 ultra-shallow profiles was performed in Changbaishan Tianchi volcanic region in 2002. The result shows that there are three （in some areas as many as seven） stable interfaces in the survey region, but no reflection phases are found in depths greater than 500 m. The number of interfaces in the southwestern part is obviously greater than in the northwestern part of Tianchi volcano, which suggests that the faults in the southwest have a stronger controlling power over the flow direction of volcano-spewed lava as compared with those in the northwest. Six shallow faults exist in the survey region. The shallow faults are nearly vertical graben-like faults and are mostly distributed on the southwest of Tianchi crater, indicating that volcanic activities in the southwest are stronger than in the northwest. On this ground, it could be further deduced that the NE-trending major fault of Tianchi volcano （ the Liudaogou-Tianchi-Zengfengshan fault） is more active than the NW-trending Baishanzhen-Tianchi-Jince fault.

2-D crustal Poisson′s ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.

长白山天池火山西南麓水压致裂法地应力测量及其实测数据在断裂稳定性分析中的应用

长白山天池火山是一座新生代多成因复合火山,其活动性一直受到地学界的高度重视.而地应力测量数据对于了解火山的活动情况等具有重要意义,但目前长白山天池火山地区实测地应力资料较少.为了更准确地了解长白山天池火山地区现今地应力状态及断裂稳定性,在长白山天池火山西南麓MJZ测点0~300 m孔深开展了水压致裂法地应力测量.利用此次实测地应力数据,本文首先分析了该地区地壳浅表层应力状态,结果表明:①测区以水平构造应力为主导,应力值与其他地区相比,相对较低;②SH(最大水平主应力)、Sh(最小水平主应力)和Sv(垂向主应力)均随深度增加而基本呈线性增大趋势;在60~180 m深度,三者展现为逆断层应力状态,即SH>Sh>Sv;在180~300 m,则表现为SH>Sv>Sh,该应力关系有利于走滑断层活动;③钻孔上部SH方向为N38°E,与东北地区构造应力场方向基本一致.钻孔下部由于受区内NW向断裂和其他因素影响,存在与区域主应力方向有偏差的局部应力场.其次,基于实测应力数据,应用库仑摩擦滑动准则,并取摩擦系数为0.6和1.0,初步评价了区域断裂的稳定性.结果显示,研究区现今应力状态尚未达到断裂失稳滑动水平,推测测区断裂目前相对稳定.结合其较低的应力积累水平,一定程度上反映出长白山天池火山区目前没有明显活动,地壳总体是稳定的.本文的研究结果可为长白山天池火山的活动性、地震地质等研究提供地应力方面的基础数据,同时也为测区地质环境安全评价提供参考依据.