Geomorphology of subglacial volcanoes in the Azas Plateau, the Tuva Republic, Russia

The Azas Plateau volcanic field is located in the Tuva Republic of the Russian Federation. The compositions of the Azas Plateau volcanics include low-viscosity trachybasalt and basanite. Volcanic edifices of Middle-Late Pleistocene age are widely distributed in the southeastern part of the volcanic field. There are subglacial volcanoes among the volcanic edifices, and their formation coincided with extensive ancient glaciations in the region. The dominant subglacial volcanoes in the area are tuyas. The general shapes of the tuyas (flat-tops with steep sides) are due to eruptions into meltwater lakes and confinement of ice walls, and effusive subaerial eruptions of basaltic lavas. There are also non-flat-topped subglacial volcanoes and at least one subaerial volcanic edifice in the area. Degradation appears to have modified the primary shapes of the tuya edifices, and such processes seem to include failures of over-steepened slopes, gully formation due to stream runoff and debris flows, cirque/valley glaciation, and modification by rock glaciers. The estimated thicknesses of the ice sheets covering the subglacial volcanoes during their eruptions range 300–600 m on average.     

Modelling of ground deformation and gravity fields using finite element method: an application to Etna volcano

Elastic finite element models are applied to investigate the effects of topography and medium heterogeneities on the surface deformation and the gravity field produced by volcanic pressure sources. Changes in the gravity field cannot be interpreted only in terms of gain of mass disregarding the ground deformation of the rocks surrounding the source. Contributions to gravity changes depend also on surface and subsurface mass redistribution driven by dilation of the volcanic source. Both ground deformation and gravity changes were firstly evaluated by solving a coupled axisymmetric problem to estimate the effects of topography and medium heterogeneities. Numerical results show significant discrepancies in the ground deformation and gravity field compared to those predicted by analytical solutions, which disregard topography, elastic heterogeneities and density subsurface structures. With this in mind, we reviewed the expected gravity changes accompanying the 1993–1997 inflation phase on Mt Etna by setting up a fully 3-D finite element model in which we used the real topography, to include the geometry, and seismic tomography, to infer the crustal heterogeneities. The inflation phase was clearly detected by different geodetic techniques (EDM, GPS, SAR and levelling data) that showed a uniform expansion of the overall volcano edifice. When the gravity data are integrated with ground deformation data and a coupled FEM modelling was solved, a mass intrusion could have occurred at depth to justify both ground deformation and gravity observations.     

SANARIS Project: A Satellite Network for Natural Risk Monitoring

A new satellite communication system specificallydesigned for low-rate data applications has beendeveloped and prototyped. A validation project isproposed to install a pilot network to be operated for6 months. One of the target markets related tovolcanoes, has been selected, so that a group of usersis integrated in the project. A specific applicationfor this market will be developed regarding dataacquisition, processing, storage and dissemination todistant users. The feasibility of using the newsatellite system to provide a new Eutelsat service forlow-rate data applications, will be evaluated from theperformance of the pilot network. The system ofautomatic acquisition, field storage and communicationwith the local control center is already functioning,as well as the circulation of information viaInternet. The development of the application andtransmission via satellite to distant users is stillin an evaluation phase for the volcanoes of Timanfaya(Lanzarote, Canary Island), Vesuvius (Naples) and SeteCidades Caldera (Sao Miguel, Azores Islands).     

Seismic pattern recognition techniques to predict large eruptions at the Popocatépetl,Mexico, volcano

Using pattern recognition techniques, we formulate a simple prediction rule for a retrospective prediction of the three last largest eruptions of the Popocatépetl, Mexico, volcano that occurred on 23 April–30 June 1997 (Eruption 1; VEI ~ 2–3); 11 December 2000–23 January 2001 (Eruption 2; VEI ~ 3–4) and 7 June–4 September 2002 (Eruption 3; explosive dome extrusion and destruction phase). Times of Increased Probability (TIP) were estimated from the seismicity recorded by the local seismic network from 1 January 1995 to 31 December 2005. A TIP is issued when a cluster of seismic events occurs under our algorithm considerations in a temporal window several days (or weeks) prior to large volcanic activity providing sufficient time to organize an effective alert strategy. The best predictions of the three analyzed eruptions were obtained when averaging seismicity rate over a 5-day window with a threshold value of 12 events and declaring an alarm for 45 days. A TIP was issued about six weeks before Eruption 1. TIPs were detected about one and four weeks before Eruptions 2 and 3, respectively. According to our objectives, in all cases, the observed TIPs would have allowed the development of an effective civil protection strategy. Although, under our model considerations the three eruptive events were successfully predicted, one false alarm was also issued by our algorithm. An analysis of the epicentral and depth distribution of the local seismicity used by our prediction rule reveals that successful TIPs were issued from microearthquakes that took place below and towards SE of the crater. On the contrary, the seismicity that issued the observed false alarm was concentrated below the summit of the volcano. We conclude that recording of precursory seismicity below and SE of the crater together with detection of TIPs as described here, could become an important tool to predict future large eruptions at Popocatépetl. Although our model worked well for events that occurred in the past, it is necessary to verify the real capability of the model for future eruptive events.     

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

One of largest eruptions in the Tianchi volcano during the Holocene occurred in about 1000 years ago[1―3]. The volcanic ash erupted had been found in Japan, which is more than 1000 km from the Tianchi volcanic vent[4,5]. Moreover, this eruption has been recognized in the study of Greenland ice core (GISP2)[6,7]. There have been many studies about eruption products of the Tianchi volcano, which dominantly focused on petrological, geochemical and volcanic eruptive dynamic aspects[8―10]. On…     

2017年全球活动火山时空分布以及阿贡火山喷发前后的形变特征

归纳总结2017年度全球81座活火山的活动情况,共计活动1058座次,平均每周记录20座活火山的活动信息。根据火山潜在喷发的危险性和火山活动的强弱程度对上述火山进行分级描述,火山活动主要反映了地球表层的构造活动,其中大角度俯冲带的弧后火山最为强烈,小角度的俯冲带、拉张裂谷和走滑为主的板块边界火山活动较为平静,火山活动频繁的印度尼西亚岛链是受灾最为严重的区域。预计全球火山活动将进一步加剧,印尼岛链受火山灾害威胁的程度依然较大。位于印尼岛链巴厘岛上的阿贡火山自2017年9月开始活动以来,整个喷发过程极具代表性,监测阿贡火山喷发过程可为全球典型火山喷发事件研究提供参考。     

内蒙锡林浩特鸽子山火山地质研究

鸽子山火山位于内蒙古自治区锡林浩特市东南,处于大兴安岭-大同新生代火山喷发带中段,是锡林浩特-阿巴嘎火山群中保存最为完好的一座玄武质火山。火山喷发物的分布面积约55km²,主要为降落火山渣、溅落熔结火山碎屑岩和熔岩流,成分主要为碧玄岩,晚期有少量的橄榄拉斑玄武岩,碧玄岩中含有较多二辉橄榄岩包体和辉石及歪长石巨晶。火山由锥体、熔岩流和火山碎屑席组成,锥体由早期的降落锥和晚期溅落锥复合而成。火山口经历多次塌陷而成为破火口。锥体西侧及北东侧出露两个仍保留了原始形态的熔岩溢出口,熔岩流类型为结壳熔岩,由多个岩流单元组成,局部地区的熔岩流中发育较多保存完好的喷气锥、喷气碟或喷气塔。火山碎屑席主要分布在锥体的东侧,厚度由锥体向外逐渐减薄。火山活动可分为早、晚两个阶段,早期为爆破式喷发,形成火山渣锥和碎屑席,属亚布里尼型喷发,晚期主要为溢流式喷发,形成溅落锥和大规模熔岩流,其活动时代为晚更新世末-全新世。     

Continuous chemical monitoring of volcanic gas in Izu-Oshima volcano, Japan

A new continuous monitoring system has been developed for the measurement of volcanic gas from the steam well located 3 km north from the summit of Izu-Oshima volcano, Japan. After removing the water vapor using three sequential dehydration methods, CO₂ and SO₂ contents are measured using IR sensors, and O₂ and H₂ using a zirconia sensor and a semiconductor sensor, respectively. This system has been in operation without any significant trouble for 3 years.The dehydrated volcanic gas from the well consists of a mixture of CO₂, O₂ and N₂. A decreasing trend of the CO₂ content was observed from 1995 to 1998 together with a decrease of volcanic activity. Seasonal changes have also been observed in CO₂ and O₂ contents, CO₂ being higher and O₂ lower in summer, which suggests larger contribution of magmatic components in summer. While changes in short-term variation in CO₂ and O₂ are influenced by atmospheric pressure changes; the CO₂ content correlates inversely with atmospheric pressure unlike O₂ with some hours delay. In contrast, the H₂ content increased intermittently up to 1200 ppm one to several hours after a sudden drop in the atmospheric pressure and without any apparent correlation with seasonal changes.This system allows us to study temporal variation in chemical composition of volcanic gas during quiescent periods of volcanic activity of Izu-Oshima volcano, and might help us detect anomalous changes before future eruptive events.     

干涉合成孔径雷达及其在火山研究中的应用(第二部分:阿拉斯加火山的InSAR成像)(英文)

干涉合成孔径雷达是一项能够对地表变形进行测量的遥感技术,在一个巨大区域内,它的变形测量精度可达亚厘米级,而其空间分辨率则在数十米以内。本文对我们应用InSAR技术对阿拉斯加火山进行研究的最新成果进行了总结,同时包括火山的喷发和非喷发活动。这些研究成果表明InSAR不仅能够增进我们对阿拉斯加火山活动的理解,而且还能够增强我们对未来火山喷发情况及其灾害的预测能力。     

高分五号大气痕量气体差分吸收光谱仪观测数据的火山喷发SO2总量反演

火山喷发产生的高浓度SO₂气体及其远距离输送会对全球气候变化和航空飞行安全产生重要影响。卫星遥感技术以大面积连续观测、高时空分辨率等优势成为大气SO₂监测的重要手段之一。作为中国第一颗紫外可见光波段的高光谱载荷,高分五号卫星大气痕量气体差分吸收光谱仪（GF-5 EMI）通过探测地球大气或表面反射、散射的紫外辐射来解析SO₂总量的分布和变化。本文首先基于大气辐射传输模型SCIATRAN,选择中低纬地区地表类型均一的海洋区域像元,模拟了典型大气条件下的晴空天顶反照率,用以评价EMI载荷天顶观测光谱的精度。其次,基于TROPOMI L1 Radiance辐亮度数据和DOAS反演原理,经477 nm O₄云筛选、光谱定标、慢变剔除、斜柱转垂直柱等步骤后,获得同一火山喷发区域的SO₂总量反演结果并与TROPOMI官方offline L2 SO₂产品进行对比分析。最后,利用GF-5 EMI UV-2通道观测数据,采用DOAS算法反演获得GF-5 EMI大气SO₂总量,并将反演结果与国际同类载荷S5P/TROPOMI SO₂总量结果进行比较分析,评判GF-5 EMI在全球火山活动SO₂变化监测方面的能力。结果显示,300—400 nm波段范围内,海洋区域采样点EMI观测光谱值低于SCIATRAN模拟光谱值,EMI与TROPOMI观测光谱呈现出相似的系统性偏差。基于高空间高光谱分辨率的TROPOMI L1 Radiance辐亮度数据、315—327 nm、325—335 nm和360—390 nm共3个波段窗口、以及上述DOAS反演原理获得的SO₂结果与TROPOMI官方发布的offline L2 SO₂产品结果相关性较高,两者的相关系数可达到0.97—0.99,相对偏差在3%—9%。GF-5 EMI能够获取火山喷发SO₂排放的时空分布特征,并与国际同类载荷TROPOMI反演结果具有较高的空间一致性,能够满足全球火山喷发监测、预警及其气候影响研究的应用需求。