Deformation and seismic precursors to dome-collapse and fountain-collapse nuées ardentes at Merapi Volcano, Java, Indonesia, 1994–1998     

B. Voight  K. D. Young  D. Hidayat  Subandrio  M. A. Purbawinata  A. Ratdomopurbo  Suharna  Panut  D. S. Sayudi  R. LaHusen  J. Marso  T. L. Murray  M. Dejean  M. Iguchi  K. Ishihara 《Journal of Volcanology and Geothermal Research》2000,100(1-4)

Following the eruption of January 1992, episodes of lava dome growth accompanied by generation of dome-collapse nuées ardentes occurred in 1994–1998. In addition, nuées ardentes were generated by fountain-collapse in January 1997, and the 1998 events also suggest an explosive component. Significant tilt and seismic precursors on varying time scales preceded these events. Deformation about the summit has been detected by electronic tiltmeters since November 1992, with inflation corresponding generally to lava dome growth, and deflation (or decreased inflation) corresponding to loss of dome mass. Strong short-term (days to weeks) accelerations in tilt rate and seismicity occurred prior to the major nuées ardentes episodes, apart from those of 22 November 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short-term precursors. Because of the combination of populated hazardous areas and the lack of an issued warning, about 100 casualties occurred in 1994. In contrast, the strong precursors in 1997 and 1998 provided advance warning to observatory scientists, enabled the stepped raising of alert levels, and aided hazard management. As a result of these factors, but also the fortunate fact that the large nuées ardentes did not quite descend into populated areas, no casualties occurred. The nuée ardente episode of 1994 is interpreted as purely due to gravitational collapse, whereas those of 1997 and 1998 were influenced by gas-pressurization of the lava dome.  相似文献   

Combined unspiked K–Ar and 40Ar/39Ar dating applied to the dating of 80–260 ka old Icelandic sub-glacial rhyolites     

《Quaternary Geochronology》2023

We have used two techniques (i.e. K–Ar and ⁴⁰Ar/³⁹Ar) on Icelandic obsidian samples to produce and more specially to estimate the quality and accuracy of the ages that can be obtained. Following a meticulous protocol, we were able to date six rhyolitic eruptions with an accuracy 7 to 40 times better than those obtained previously. Among these six rhyolites are the first published K–Ar and ⁴⁰Ar/³⁹Ar ages of Krafla.The combined K–Ar and ⁴⁰Ar/³⁹Ar approach produces not only highly precise but also accurate ages. Such high precision makes it possible to produce accurate reconstructions of ice thickness at a given location and time, to test whether there was a possible link between deglaciation and rhyolitic volcanism onset in Iceland, and to explore other possible applications of the ⁴⁰Ar/³⁹Ar dating method to paleo-environmental and paleo-climatic reconstruction at Iceland's latitude.Then, we investigate, by combining geochemistry (i.e. determination of major and trace element composition) and geochronology (i.e. dating of rhyolitic eruptions via K–Ar and ⁴⁰Ar/³⁹Ar dating) for a number of Icelandic rhyolitic volcanoes whose activity could be recorded in North Atlantic sedimentary cores as well as in Arctic ice. The aim of this approach is to provide new independent anchors and correlations between climate records. Of the six dated eruptions, we propose that one is record in North Atlantic sediments, the Loðmundur eruption that constitutes one of the Kerlingarfjöll tuyas, which we date at 189.9 ± 1.1 ka and assume to be the source of the tephra recognized in core MD04-2822 at a depth of 3630–3631 cm.  相似文献   

Soil erodibility as impacted by vegetation restoration strategies on the Loess Plateau of China     

Hao Wang  Guang-hui Zhang  Ning-ning Li  Bao-jun Zhang  Han-yue Yang 《地球表面变化过程与地形》2019,44(3):796-807

Near soil surface characteristics change significantly with vegetation restoration, and thus, restoration strategies likely affect soil erodibility. However, few studies have been conducted to quantify the effects of vegetation restoration strategies on soil erodibility in regions experiencing rapid vegetation restoration. This study was conducted to evaluate the effects of vegetation restoration strategies on soil erodibility, reflected by soil cohesion (Coh), penetration resistance (PR), saturated conductivity (K_s), number of drop impacts (NDI), mean weight diameter of soil aggregates (MWD), and soil erodibility K factor on the Loess Plateau. One slope farmland and five 25-year-restored lands covered by old world bluestem, korshinsk peashrub, shrub sophora, sea-buckthorn, and black locust were selected as test sites. The old world bluestem was restored via natural succession, while the other four lands were restored by artificial planting. A comprehensive soil erodibility index (CSEI) was produced by a weighted summation method to quantify the effects of vegetation restoration strategies on soil erodibility completely. The results showed that Coh, K_s, NDI, and MWD of the five restored lands were greater than those of the slope farmland. However, the PR and K of the five restored lands were less than those of the slope farmland. CSEI varied greatly under different restoration strategies, from 1 to 0.214. Compared with the control, these indices decreased on average by 68.2%, 78.6%, 72.7%, 75.8%, and 62.8% for old world bluestem, korshinsk peashrub, shrub sophora, sea-buckthorn, and black locust, respectively. The variation in soil erodibility was significantly influenced by biological crust thickness, bulk density, organic matter content, plant litter density, and root mass density. Shrub-lands via artificial planting, especially korshinsk peashrub, were considered the most effective restoration strategies to reduce soil erodibility on the Loess Plateau. The results are helpful for selecting vegetation restoration strategies and asking their benefits in controlling soil erosion. © 2018 John Wiley & Sons, Ltd.  相似文献   

A numerical model of coastline deformation for sandy beach at downstream of a jetty     

SUN Linyun  PAN Junning  XING Fu  LIU Jiaju 《海洋学报(英文版)》2004,23(1):169-178

A reformed numerical model based on the “one-line theory” for beach deformation is presented. In this model, the change of beach slope during coastline procession is considered.A wave numerical model combined with wave refraction, diffraction and reflection is used to simulate wave climate to increase numerical accuracy.The results show that the numerical model has a good precision based on the adequate field data. The results can be applied to practical engineering.  相似文献   

Early to mid-Viséan shallow water platform buildups,north Co. Dublin,Ireland     

Ian D. Somerville  Neil A. H. Pickard  Peter Strogen  Garethli Jones 《Geological Journal》1992,27(2):151-172

A number of carbonate buildups in north Co. Dublin, long assigned to the late Viséan (Asbian), are shown on the basis of coral, foraminiferal and algal evidence to be early to mid-Viséan (late Chadian to Holkerian) in age. They are equivalent in age to beds ranging from the upper part of the Lane Formation to the top of the Holmpatrick Formation. The buildups are poorly exposed and relatively small, probably only a few tens of metres across at most. Buildup sediments are massive to crudely bedded and dominated by peloidal, clotted and dense uniform micrites displaying lime mudstone and bioclastic wackestone textures. Dasycladacean algae are common in the buildups and cryptalgal fabrics are locally important. Cavities in the buildups are generally small (< 5 cm) and lined with inclusion-rich radiaxial calcite cements. Micritization of bioclasts and cements is ubiquitous. Enclosing off-buildup limestones are skeletal and intraclastic grainstones possessing sedimentary structures indicative of deposition in moderate to high energy environments. Fossil and petrographic evidence from the buildups also indicate a shallow water origin for the north Co. Dublin buildups. Compared with the slightly older Tournaisian (Courceyan to early Chadian) Waulsortian buildups which developed extensively in the Dublin Basin, these younger platform buildups are smaller and more isolated and possess a diverse suite of algal components and cryptalgal fabrics. Nevertheless, components in the north Co. Dublin buildups most closely resemble the shallowest phase D Waulsortian buildups, particularly in the presence of abundant peloids and micritized cements. The north Co. Dublin buildups developed on a carbonate platform (the Milverton Platform), adjacent to the Dublin Basin, whereas the Waulsortian developed in a deeper ramp setting. Following the demise of the Waulsortian in early Chadian time carbonate buildups established themselves on the shallow platforms. It is suggested that the microbial communities responsible for these buildups may have ‘evolved’ from older phase D Waulsortian communities and that he north Co. Dublin platform buildups represent the shallow water end of a spectrum of Viséan buildups.  相似文献   

Numerical identification of tsunami boulders and estimation of local tsunami size at Ibaruma reef of Ishigaki Island,Japan          下载免费PDF全文

Masashi Watanabe  Kazuhisa Goto  Fumihiko Imamura  Chuki Hongo 《Island Arc》2016,25(5):316-332

Tsunami boulders deposited along the coast constitute important geological evidence for paleotsunami activity. However, boulders can also be deposited by large storm waves. Although several sedimentological and theoretical methods have been proposed to differentiate tsunami and storm wave affected boulders, no appropriate numerical method exists for their differentiation. Therefore, we developed a new numerical scheme to differentiate tsunami and storm wave boulders for coastal boulders on Ishigaki Island, Japan. In this area, tsunami and storm waves have emplaced numerous boulders on the reef and the coast. By conducting numerical calculations of storm waves in this region, we estimated the size of a storm wave that can explain the maximum clast size distribution of boulders on the reef. Consequently, we showed that a wave with a combination of 8 m in initial wave height and 10 s period can satisfy the above conditions when we assume mean sea level. In contrast to the boulders on the reef, all boulders deposited along the shore are heavier than the calculated possible maximum clast size distribution by the storm wave. Therefore, we confirmed these boulders as being of tsunami origin. Results of previous studies showed that they were most likely deposited or reworked by the 1771 Meiwa tsunami. Then, using the tsunami boulders, we numerically estimated the wave period and amplitude of the 1771 Meiwa tsunami, which should have had a 4–5 min period and 5.6–5.9, 6.3–7.0 m amplitude, respectively. Using the proposed scheme, it is possible to differentiate tsunami and storm wave boulders and estimate the size of past storm waves and tsunami waves, although it is noteworthy that there are exceptions for which the scheme cannot be applied.  相似文献   

Petrogenesis and geodynamic significance of the Ganhe Formation lavas,eastern Great Xing'an Range,China: Evidence from geochemistry and geochronology          下载免费PDF全文

A‐lei Gu  Jing‐gui Sun  Ling‐an Bai  Yong Zhang  Pei‐long Cui  Peng Chai  Ke‐qiang Zhao  Qing‐long Sun  Liang Ren  Yan‐jun Chen  Jun‐quan Zhu 《Island Arc》2016,25(2):87-110

Mesozoic volcanic rocks are widespread throughout the Great Xing'an Range of northeastern China. However, there has been limited investigation into the age and petrogenesis of the Mesozoic volcanics in the eastern Great Xing'an Range. According to our research, the volcanic rocks of the Dayangshu Basin, eastern Great Xing'an Range are composed mainly of trachybasalt, basaltic andesite, and basaltic trachyandesite, with minor intermediate–basic pyroclastic rocks. In this study, the geochemistry and geochronology of the Mesozoic volcanic rocks are presented in order to discuss the petrogenesis and tectonic setting of the Ganhe Formation in the Dayangshu Basin. Zircon U–Pb dating by laser ablation inductively coupled plasma–mass spectrometry indicates that the Mesozoic lavas formed during the late Early Cretaceous (114.3–108.8 Ma). This suite of rocks exhibits a range of geochemical signatures indicating subduction‐related genesis, including: (i) calc‐alkaline to high‐K calc‐alkaline major element compositions; (ii) enrichment of large ion lithophile elements (e.g. Rb, Ba, K) and light rare earth elements (LREEs/HREEs =7.33–9.85); and (iii) weak depletion in high field strength elements (e.g. Nb, Ta, Ti). Furthermore, Sr–Nd–Pb isotopic data yield initial ⁸⁷Sr/⁸⁶Sr values of 0.70450–0.70463, positive ε_Nd(t) values of +1.8 to +3.3, and a mantle‐derived lead isotope composition. Combined with the regional tectonic evolution, the results of this study suggest that the Ganhe Group lavas are derived from decompression melting of a metasomatized (enriched) lithospheric mantle, related to asthenospheric upwelling, which resulted from lithospheric mantle delamination and produced extension of the continental margin following the subduction of the Paleo‐Pacific Plate.  相似文献   

Pertrogenesis and tectonic implications of the late Jurassic basic rocks from the northern Shi‐Hang zone,Southeast China          下载免费PDF全文

Qing Zhou  Yao–hui Jiang  Shi–yong Liao  Peng Zhao  Ru–ya Jia  Zheng Liu  Guo–chang Wang  Chun–yu Ni 《Island Arc》2016,25(3):235-250

The tectonic setting of the late mesozoic of South China is in a debate between two schools of thought: an intra‐continental rift zone along a passive continental margin or active rifting associated with subduction of the paleo‐Pacific Plate. In this study, we present new sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb zircon ages, along with geochemical data of three basic dikes that cross‐cut the Dexing porphyry copper deposit. The deposit is the largest of its kind in eastern China and part of large scale mineralization associated with Mesozoic magmatic activity in the area. Our results indicate that the dikes were emplaced in the Late Jurassic with an average U‐Pb age of 153.5 ± 2.4 Ma. The intrusions have bulk ε_Nd(t) of ca +0.7 and zircon ε_Hf(t) value of +1.54 to +6.92. Based on relatively enriched light rare earth elements (LREE) and depleted high‐field‐strength elements (HFSE) abundances with pronounced negative Ta–Nb, Hf–Zr and Ti anomalies in multi‐element diagrams, we propose that these dikes were derived from a subduction‐modified lithospheric mantle source. The variability in Hf isotopes identifies some degree of crustal contaminations. Our data support a scenario with a back‐arc extensional setting or an intra‐arc rift environment associated with the westward subduction of the paleo‐Pacific Plate at or prior to the late Jurassic as the most likely cause for these subduction signatures.  相似文献   

Geochemical and Sr–Nd isotopic constraints on the petrogenesis of the Goesan monzodiorite pluton in the central Okcheon belt,Korea          下载免费PDF全文

Chang‐Sik Cheong  Hui Je Jo  Youn‐Joong Jeong  Chan‐Soo Park  Moonsup Cho 《Island Arc》2016,25(1):43-54

The Permian–Triassic high pressure metamorphism and potassic magmatism in central Korea attest to the extension of the Dabie‐Sulu collision belt in central‐eastern China towards the Korean Peninsula and possibly the Japanese Islands. We present major and trace element and Sr–Nd isotope data for a ca. 230 Ma monzodiorite pluton emplaced in the Goesan area, central Okcheon belt, Korea. This pluton shows geochemical features comparable with those of the coeval monzonite–syenite–gabbro–mangerite suite documented recently in the Gyeonggi massif. The metaluminous and alkali–calcic signatures of the Goesan intrusives correspond to the Caledonian‐type post‐orogenic granitoids. The K₂O/Na₂O ratios of all analyzed samples are greater than 1, and are not correlative with their SiO₂ contents. The enrichment of both large‐ion‐lithophile elements and highly compatible elements in the Goesan pluton is probably indicative of metasomatized mantle origin. The elemental fractionation in the source region must have occurred in the distant past, possibly the Paleoproterozoic, to generate significantly negative ε_Nd(t) values (< –16). Chondrite‐normalized rare earth element patterns as well as Rb/Sr and Ba/Rb ranges suggest that the source consists of amphibole‐bearing rocks. Progressive decreases in negative Eu anomaly and Ba, Sr, Ni, Cr and V contents with increasing SiO₂ contents reflect an important role of plagioclase, biotite and hornblende for the fractionation process. Zr is undersaturated in the potassic, metaluminous melt. The initial Sr–Nd isotopic compositions of the samples are correlated with their SiO₂ contents, substantiating a role of crustal assimilation during the magmatic differentiation. The Sr–Nd elemental and isotopic modeling suggests that the Goesan pluton was initially slightly heterogeneous in its isotopic composition, and underwent concurrent assimilation and fractional crystallization. The occurrence of the Goesan pluton provides further evidence corroborating the amalgamation of allochthonous terranes within the Okcheon belt during the Permian–Triassic collisional orogeny.  相似文献   

A multi‐geochronological study of the Hakusan volcano,central Japan          下载免费PDF全文

Noriko Hasebe  Yasuyuki Nakano  Hikaru Miyamoto  Toshio Higashino  Akihiro Tamura  Shoji Arai  Ju‐Yong Kim 《Island Arc》2016,25(2):111-125

The Hakusan volcano, central Japan, is located in a region where two subducting plates (the Pacific Plate and the Philippine Sea Plate) overlap near the junction of four plates adjacent to the Japanese Islands (the Pacific Plate, the Philippine Sea Plate, the Eurasia Plate, and the North American Plate). The Hakusan volcano consists of products from four major volcanic episodes: Kagamuro, Ko‐hakusan, and Shin‐Hakusan I and II. To date the eruption events of the Hakusan volcano we applied thermoluminescence and fission track methods. ²³⁸U(²³⁴U)–²³⁰Th disequilibrium and ²⁰⁶Pb/²³⁸U methods were applied to date the zircon crystallization ages for estimating the magma residence time before the eruptions. The eruption ages we obtained are ca 250 ka for Kagamuro, ca 100 ka and ca 60 ka for Ko‐Hakusan, ca 50 ka for Shin‐Hakusan I, and <10 ka for Shin‐Hakusan II. They are concordant with previous reports based on K–Ar dating. Some of the pyroclastic rocks, possibly originating from Shin‐Hakusan II activities, are dated to be ca 36 ka or 50 ka, and belong to the Shin‐Hakusan I activity. The zircon crystallization ages show several clusters prior to eruption. The magma residence time was estimated for each volcanic activity by comparing the major crystallization events and eruption ages, and we found a gradual decrease from ca. 500 ky for the Kagamuro activity to ca. 5 ky for the Shin‐Hakusan II activity. This decrease in residence time may be responsible for the decrease in volume of erupted material estimated from the current topography of the region. The scale of volcanic activity, which was deduced from the number of crystallized zircons, is more or less constant throughout the Hakusan volcanic activity. Therefore, the decrease in magma residence time is most likely the result of stress field change.  相似文献