首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Understanding the characteristics of volcanic thermal emissions and how they change with time is important for forecasting and monitoring volcanic activity and potential hazards. Satellite instruments view volcanic thermal features across the globe at various temporal and spatial resolutions. Thermal features that may be a precursor to a major eruption, or indicative of important changes in an on-going eruption can be subtle, making them challenging to reliably identify with satellite instruments. The goal of this study was to explore the limits of the types and magnitudes of thermal anomalies that could be detected using satellite thermal infrared (TIR) data. Specifically, the characterization of sub-pixel thermal features with a wide range of temperatures is considered using ASTER multispectral TIR data. First, theoretical calculations were made to define a “thermal mixing detection threshold” for ASTER, which quantifies the limits of ASTER's ability to resolve sub-pixel thermal mixing over a range of hot target temperatures and % pixel areas. Then, ASTER TIR data were used to model sub-pixel thermal features at the Yellowstone National Park geothermal area (hot spring pools with temperatures from 40 to 90 °C) and at Mount Erebus Volcano, Antarctica (an active lava lake with temperatures from 200 to 800 °C). Finally, various sources of uncertainty in sub-pixel thermal calculations were quantified for these empirical measurements, including pixel resampling, atmospheric correction, and background temperature and emissivity assumptions.  相似文献   

2.
An explosive eruption occurred at the summit of Bezymianny volcano (Kamchatka Peninsula, Russia) on 11 January 2005 which was initially detected from seismic observations by the Kamchatka Volcanic Eruption Response Team (KVERT). This prompted the acquisition of 17 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite images of the volcano over the following 10 months. Visible and infrared data from ASTER revealed significant changes to the morphology of the summit lava dome, later seen with field based thermal infrared (TIR) camera surveys in August 2005. The morphology of the summit lava dome was observed to have changed from previous year’s observations and historical accounts. In August 2005 the dome contained a new crater and two small lava lobes. Stepped scarps within the new summit crater suggest a partial collapse mechanism of formation, rather than a purely explosive origin. Hot pyroclastic deposits were also observed to have pooled in the moat between the current lava dome and the 1956 crater wall. The visual and thermal data revealed a complex eruption sequence of explosion(s), viscous lava extrusion, and finally the formation of the collapse crater. Based on this sequence, the conduit could have become blocked/pressurized, which could signify the start of a new behavioural phase for the volcano and lead to the potential of larger eruptions in the future.  相似文献   

3.
The Chaman left‐lateral strike‐slip fault bounds the rigid Indian plate boundary at the western end of the Himalayan‐Tibetan orogen and is marked by contrasting topographic relief. Deformed landforms along the fault provide an excellent record for understanding this actively evolving intra‐continental strike‐slip fault. The geomorphic response of an active transpessional stretch of the Chaman fault was studied using digital elevation model (DEM) data integrated with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Visible and Near Infrared/Short Wave Infrared (VNIR/SWIR) and images from GeoEye‐1. Geologic and geomorphic mapping helped in reconstructing the Late Quaternary landscape history of this transpessional strand of the Chaman strike‐slip fault and the associated Spinatizha thrust fault in western Pakistan. Topographic analysis of a part of the transpression (the thrust bounded Roghani ridge) revealed northward growth of the Spinatizha fault with the presence of three water gaps and two corresponding wind gaps. Geomorphic indices including stream length‐gradient index, mountain front sinuosity, valley floor width to valley height ratios, and entrenchment of recent alluvial fan deposits were used to define the lateral growth and direction of propagation of the Spinatizha fault. Left‐lateral displacement along Chaman fault and uplift along the Spinatizha fault was defined using topographic analysis of the Roghani ridge and geomorphic mapping of an impressive alluvial fan, the Bostankaul fan. The landforms and structures record slip partitioning along the Indian plate boundary, and account for the convergence resulting from the difference in the Chaman fault azimuth and orientation of the velocity vector of the Indian plate. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
A combination of field mapping, geochemistry, and remote sensing methods has been employed to determine the extent of hydrothermal alteration and assess the potential for failure at the Santiaguito lava dome complex, Guatemala. The 90-year-old complex of four lava domes has only experienced relatively small and infrequent dome collapses in the past, which were associated with lava extrusion. However, existing evidence of an active hydrothermal system coupled with intense seasonal precipitation also presents ideal conditions for instability related to weakened clay-rich edifice rocks. Mapping of the Santiaguito dome complex identified structural features related to dome growth dynamics, potential areas of weakness related to erosion, and locations of fumarole fields. X-ray diffraction and backscattered electron images taken with scanning electron microscopy of dacite and ash samples collected from around fumaroles revealed only minor clay films, and little evidence of alteration. Mineral mapping using ASTER and Hyperion satellite images, however, suggest low-temperature (<150 °C) silicic alteration on erosional surfaces of the domes, but not the type of pervasive acid-sulfate alteration implicated in collapses of other altered edifices. To evaluate the possibility of internal alteration, we re-examined existing aqueous geochemical data from dome-fed hot springs. The data indicate significant water–rock interaction, but the Na–Mg–K geoindicator suggests only a short water residence time, and δ18O/δD ratios show only minor shifts from the meteoric water line with little precipitation of secondary (alteration) minerals. Based on available data, hydrothermal alteration on the dome complex appears to be restricted to surficial deposits of hydrous silica, but the study has highlighted, importantly, that the 1902 eruption crater headwall of Santa María does show more advanced argillic alteration. We also cannot rule out the possibility of advanced alteration within the dome complex interior that is not accessible to the methods used here. It may therefore be prudent to employ geophysical methods to make further assessments in the future.  相似文献   

5.
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a useful tool for detecting low quantities of sulfur dioxide at passively degassing volcanoes such as Lascar volcano, Chile. Two mini-UV spectrometers (MUSes) were used to make transects of Lascar volcano’s sulfur dioxide plume on December 7, 2004, during a coordinated overpass of ASTER. SO2 burdens were retrieved using the thermal infrared channels of the acquired ASTER image. This allowed for a direct comparison between the two methods in order to validate the ASTER SO2 retrieval. The results were extremely encouraging with ASTER deriving SO2 fluxes within the range of fluxes obtained by the MUSe.  相似文献   

6.

Satellite images are used extensively in studying the urban heat island (UHI) phenomenon. We evaluated the suitability of thermal infrared (TIR) data from the HJ-1B satellite for detecting UHI using a case study in Beijing. Two modified algorithms for retrieving the land surface temperature (LST) from HJ-1B data were tested. The results were compared with LST images derived from a Landsat TM thermal band and the MODIS LST output. The spatial pattern of UHI generated using HJ-1B data matched well with that produced using TM and MODIS data. Of the two algorithms, the mono-window algorithm performed better but further tests are necessary. With more frequent coverage than TM and higher spatial resolution than MODIS, the HJ-1B TIR data present a unique opportunity to study thermal environments in cities in China and neighboring countries.

  相似文献   

7.
Satellite images are used extensively in studying the urban heat island (UHI) phenomenon. We evaluated the suitability of thermal infrared (TIR) data from the HJ-1B satellite for detecting UHI using a case study in Beijing. Two modified algorithms for retrieving the land surface temperature (LST) from HJ-1B data were tested. The results were compared with LST images derived from a Landsat TM thermal band and the MODIS LST output. The spatial pattern of UHI generated using HJ-1B data matched well with that produced using TM and MODIS data. Of the two algorithms, the mono-window algorithm performed better but further tests are necessary. With more frequent coverage than TM and higher spatial resolution than MODIS, the HJ-1B TIR data present a unique opportunity to study thermal environments in cities in China and neighboring countries.  相似文献   

8.
Climate change is altering river temperature regimes, modifying the dynamics of temperature‐sensitive fishes. The ability to map river temperature is therefore important for understanding the impacts of future warming. Thermal infrared (TIR) remote sensing has proven effective for river temperature mapping, but TIR surveys of rivers remain expensive. Recent drone‐based TIR systems present a potential solution to this problem. However, information regarding the utility of these miniaturised systems for surveying rivers is limited. Here, we present the results of several drone‐based TIR surveys conducted with a view to understanding their suitability for characterising river temperature heterogeneity. We find that drone‐based TIR data are able to clearly reveal the location and extent of discrete thermal inputs to rivers, but thermal imagery suffers from temperature drift‐induced bias, which prevents the extraction of accurate temperature data. Statistical analysis of the causes of this drift reveals that drone flight characteristics and environmental conditions at the time of acquisition explain ~66% of the variance in TIR sensor drift. These results shed important light on the factors influencing drone‐based TIR data quality and suggest that further technological development is required to enable the extraction of robust river temperature data. Nonetheless, this technology represents a promising approach for augmenting in situ sensor capabilities and improved quantification of advective inputs to rivers at intermediate spatial scales between point measurements and “conventional” airborne or satellite remote sensing.  相似文献   

9.
Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8 km3 Osceola Mudflow (5600 y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz–alunite, quartz–topaz, quartz–pyrophyllite, quartz–dickite/kaolinite, and quartz–illite (all with pyrite). Clasts of smectite–pyrite and steam-heated opal–alunite–kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite–pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite–pyrite assemblages, whereas the proximal Electron Mudflow and a < 100 y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures.  相似文献   

10.
Using near simultaneously acquired Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Earth Observing-1 Advanced Land Imager (ALI) data we assess the relative radiant responses over active lava flows from the Mt. Etna July/August 2001 flank eruption. By assessing the extent of saturation between the two instruments and using the dual-band method of extracting sub pixel thermal information, we show that the ALI represents an improvement over the ETM+ in the present ability to assess temperatures of hot active lava flows for a number of reasons. (1) The extra spectral channels provided by ALI compliment the current SWIR channels on ETM+ by providing a greater number of paired channel combinations for input into the dual-band method. Thus, dual-band temperature solutions can be determined for a greater range of lava flow types than previously possible using the two paired channel combinations available with the ETM+. (2) The ALI instrument is less susceptible than ETM+ to saturation within the SWIR, especially when using channels 5, 5p and 4p at wavelengths of 1.65, 1.25 and 0.87 μm respectively. (3) The greater radiometric sensitivity of the ALI 12 bit electronics coupled with a significantly higher signal to noise ratio aid in obtaining successful dual-band solutions.  相似文献   

11.
Remote sensing classification methods can be classified as supervised and unsupervised catalogs. The maximum likelihood method (MLH) is a super-vised classification method,which is widely used in the remote sensing data classification and produces good results[1]. In the MLH, the parameters are esti-mated, assuming that the samples are normally dis-tributed in spectral space, to determine the mean vec-tor and covariance matrix of all classes. In most cases, however, the samples are not norma…  相似文献   

12.
Landsat 7 Enhanced Thematic Mapper + (ETM+) data are presented which document the thermal characteristics of a series of lava flows emplaced at Mount Etna volcano, Sicily, during 27-28 October 1999. By examining the composition of the short-wave infrared (SWIR) signal emitted from the flow surface, we identified distinctive flow units. The first unit appears to comprise recently active lava flows with relatively cool crusts which, by virtue of the integrity of this crust as determined from the ETM+ data, we infer are stationary or barely moving. The second unit is characterized by much higher levels of SWIR radiance, consistent with a channel-fed active flow unit. Analysis of the SWIR data confirm that this is fed by a lava channel, the properties of which are consistent with vigorously active channels observed on Kilauea, Hawaii. Model predictions of the maximum length that such flows could attain compare favorably with the actual flow lengths observed in the ETM+ data, indicating that the cooler flows had indeed stopped advancing, and may have attained a cooling-limited, rather than volume-limited, maximum length. Our observations and modeling provide a physical corroboration for the supposition made by Wadge (1978) in his analysis of the shape of lava flow fields on Mount Etna, which in the cooling-limited case principal flows are active one after the other and not at the same time.  相似文献   

13.
The North China Craton(NCC) experienced strong destruction(i.e., decratonization) during the Mesozoic, which triggered intensive magmatism, tectonism and thermal events and formed large-scale gold and other metal deposits in the eastern part of the craton. However, how the decratonization controls the formation and distribution of large-scale of gold and other metal deposits is not very clear. Based on a large number of published data and new results, this paper systematically summarizes all the data for the rock assemblages, chronology, geochemistry and petrogenesis of Mesozoic magmatic rocks, as well as for the mineralizing ages of gold and other metal deposits and the evolution of the Mesozoic basins in the eastern NCC. The results are used to restore the extensional rates of Mesozoic to Cenozoic basins and the strike-slip distance of the Tanlu Fault, to ascertain the location of the Paleo-Pacific plate subduction zones during the Mesozoic to Cenozoic, and to reconstruct the temporal and spatial distribution of Mesozoic gold and other metal deposits and magmatic rocks in the eastern NCC. It is obtained that the magmatism and mineralization in the eastern NCC westward migrate from east to west during the Early to Middle Jurassic, but they eastward migrate from west to east during the Early Cretaceous. The metallogenesis of these deposits is genetically related to magmatism, and the magmas provided some ore-forming materials and fluids for the generation of metal deposits. The geodynamic mechanism of decratonization and related magmatism and mineralization is proposed, i.e., the westward low-angle subduction of the Paleo-Pacific slab beneath the NCC formed continental magmatic arc with plenty of porphyry Cu-Mo-Au deposits in the Jurassic, similar to the Andean continental arc in South America. The mantle wedge was metasomatized by the fluids/melts derived from the subducting slab, laying a material foundation for hydrothermal mineralization in the Early Cretaceous. While the rollback of the subducting slab with gradually increasing subduction angle and the retreat of the subduction zones during the Early Cretaceous induced strong destruction of the craton and the formation of extensive magmatic rocks and large-scale gold and other metal deposits.  相似文献   

14.
Understanding the thermal regime of rivers is a key issue for predicting ecosystem change in the context of global warming. However, water temperature is not only influenced by air temperature. To better highlight relative contribution of factors controlling water temperature, we used satellite thermal infrared (TIR) images from Landsat ETM+ to investigate longitudinal and temporal variations in thermal patterns of the French Rh?ne River. Because satellite TIR remote sensing is limited to large rivers, we used an automated water extraction technique to remove pixels contaminated by terrestrial surfaces. We calculated water surface temperatures of the 500?km long reach for 83 dates between 1999 and 2009. The average accuracy and uncertainty of our data, ±1.1 and ±0.4°C for reaches with more than 3?pixels across and ±1.4 and ±0.5°C for reaches with one to 3?pixels across, are comparable to other satellite TIR studies of rivers. Our results confirmed previous studies on the thermal impacts of tributaries and nuclear power plants on the Rh?ne, providing an understanding of their seasonal pattern and their longitudinal impact. We showed temperature differences of 0?C2°C within the largest hydroelectric bypass facilities between the bypass section and the canal, with Montélimar and Caderousse showing the most pronounced differences. Discussion points concern the potential impacts of tributaries and nuclear power plants on the spatio-temporal thermal patterns, as well as the factors responsible for thermal differences in the bypass facilities: length and minimum flow of the bypass section, and tributaries coming into this reach.  相似文献   

15.
华北盆地滑脱构造的地震学证据   总被引：52，自引：12，他引：52       下载免费PDF全文
在华北盆地中西部的临城一巨鹿深地震反射剖面上，ＣＤＰ叠加剖面在双程走时２．５-４．５ｓ部分显示出一系列连续性好、能量强的低角度反射事件，在剖面上显示的延伸距离达４０ｋｍ．这些反射事件解释为滑脱断层，它自西向东倾角变缓，发育在深度为ｓｋｉｎ（剖面西端）至１０ｋｍ（东端）的结晶基岩中．在剖面的浅部显示出两个相似的单边断陷盆地，其主断裂以铲形归并到这一滑脱构造．上盘在伸展过程中向东滑移，拉张和重力滑动作用可能是形成这些断裂的主要原因．剖面东部的中下地壳内众多的反射事件具有叠层状的特征，并遭受强烈的变形，可能表示地幔物质上涌侵入至地壳内．岩浆侵入在地壳上部形成附加的伸展应力场，同时使下地壳增热，粘度下降，某些矿物发生脱水作用，脱出的水上移并储存于中地壳内．伸展应力场及热和水的作用促进滑脱构造的形成．邢台地震的震源深度分布表明，这一地区脆韧过渡带的深度为１０-２５ｋｍ，滑脱面为过渡带的上界面．  相似文献   

16.
我国非传统矿产资源的实例及其所涉及的科学问题   总被引：9，自引：3，他引：9  
传统矿产资源随着开采年限的增长而日益减少，寻求新的、非传统的按替资源，是解决人类矿产资源短缺的根本出路，是地球科学家长期肩负的战略性、前瞻性历史使命，我国有许多已经显示出巨大的资源潜力、但传统的矿床学、资源学、矿业技术的理论和方法难以实现其资源价值的地球物质堆积体，可视为典型的非传统矿产资源，包括：1）华南巨量堆积的天然纳米非金属矿物；2）华南微细浸染型金矿床原生矿石中的微粒金；3）西藏冈底斯中段北麓热泉泉华蛋白石中的微粒铯；4）白云鄂博等超大型矿床开采尾矿和选矿尾矿（所谓的“人工堆积矿床”）；5）部分原油和油田水中富集的金和其它金属元素；6）我国南方黑色岩系中特殊赋存状态的贵金属-重金属元素；7）我国西部陆相盆地中的可地浸砂岩型铀矿；8）我国南海和东海海域的天然气水合物；9）我国西南的分散元素矿床，由于非传统矿产资源是受目前理论、技术、经济以及环境等因素的限制尚未被认识或未能开发利用的矿产资源或潜在矿产资源，其所涉及的科学问题往往都具有显著的创新性和前沿性，对我国上述重要的非传统矿产资源而言，其所涉及的关键科学问题包括，天然纳-微米矿物及其特殊性能的成因机制，有机质与金属元素的耦合作用及其对金属富集的宏观与微观控制，等。  相似文献   

17.
龙陵-瑞丽断裂带附近的构造地貌与断裂活动性   总被引：2，自引：0，他引：2       下载免费PDF全文
利用ALOS全色、ASTER多光谱遥感影像和SRTM数字高程模型数据解译,并结合野外地质调查和实时差分GPS测量,对龙陵-瑞丽断裂带晚第四纪活动的构造地貌和地质特征进行了研究。综合遥感解译、构造地貌和地震地质调查的结果认为,龙陵-瑞丽断裂带是一条以左旋走滑作用为主的断裂,在晚第四纪具有一定的活动性;并确定了龙陵-瑞丽断裂带各活动段落的空间分布情况。选取朱家寨一带开展了探槽挖掘工作。探槽很好地揭露了基岩中发育的新鲜断层面和晚第四纪冲洪积层,但是未发现断层错动晚第四纪沉积物的迹象。采集了冲洪积层底部的植物化石进行了14C测年,结果为（1150±30）a BP。据此推测,从距今1150年以来,龙陵-瑞丽断裂带活动断层在北段未再发生过破坏性古地震事件。综合分析1976年龙陵地震的发震特点,认为1976年发生在龙陵的大地震未发生在龙陵-瑞丽断裂带上,其震源机制解和余震分布特征表明地震活动与NNW向展布的新生断裂带活动有关,这很有可能造成了NE向龙陵-瑞丽断裂带晚第四纪构造活动性减弱。  相似文献   

18.
That more than 82 percent of proved sandstone-type uranium deposits coexist with proved oil-gas or coalfields in the world reflects the fact of coexistence and accumulation of multi-energy minerals including oil, gas, coal and uranium in the same basin. Especially, this phenomenon is most typical in the Central-east Asia energy basins. Across China, Mongolia and some central Asian countries, the giant Central-east Asia metallogenetic domain (CEAMD) stretches more than 6,000 km from Songliao Basin of China in the east to the Caspian Sea in the west. The multi-energy minerals distribution characteristics of the domain include: their spatial distribution is complicated and ordered; the ore-bearing horizon relates closely to the geographical region; the accumulation/mineralization and localization time is the same or close; the occurrence setting and accumulation/mineralization have close correlation; and they have rich provenance for all the minerals. All of these imply that they have close relations between each other under a unified geodynamic background. The exogenetic uranium mineralization process in CEAMD can be divided into five phases using time limits of 100 Ma, (50±2) Ma, 20±(2–4) Ma, 8–5 Ma. The major mineralization periods and their differences in each primary uranium-bearing basin are identical to the oil-gas accumulation and localization periods and phases in the same basin, and are also in response to regional tectonics and controlled in general by the regional geodynamic environment. For industrial application and commercial exploitation, it is suggested that an important period for coexistence, accumulation and localization of oil, gas, coal and uranium and their interaction mainly occur in the late/last and post basin evolution. Through generalized analysis and comparison of accumulation/mineralization environment of the energy basins in CEAMD, the authors propose that the relatively stable regional tectonic background and moderate (weaker) structural deformation probably are necessary for formation, coexistence and preservation of large and medium-scaled sandstone-type uranium ore deposits, oil-gas fields and coalfields, while basins in favor of coexistence and accumulation are those intracratonal, intermediary massif basins and corresponding reformed basins.  相似文献   

19.
 Lascar Volcano (22°22'S, 67°44'W) is the most active volcano of the central Andes of northern Chile. Activity since 1984 has been characterised by periods of lava dome growth and decay within the active crater, punctuated by explosive eruptions. We present herein a technique for monitoring the high-temperature activity within the active crater using frequent measurements of emitted shortwave infrared (SWIR) radiation made by the spaceborne along-track scanning radiometer (ATSR). The ATSR is an instrument of low spatial resolution (pixels 1 km across) that shares certain characteristics with the MODIS instrument, planned for use as a volcano monitoring tool in the NASA EOS Volcanology Project. We present a comprehensive time series of over 60 cloud- and plume-free nighttime ATSR observations for 1992–1995, a period during which Lascar experienced its largest historical eruption. Variations in short wavelength infrared flux relate directly to changes in high-temperature surfaces within the active crater. From these data, interpretations can be made that supplement published field reports and that can document the presence and status of the lava dome during periods where direct, ground-based, observations are lacking. Our data agree with less frequent information collected from sensors with high spatial resolution, such as the Landsat thematic mapper (Oppenheimer et al. 1993) and are consistent with field observations and models that relate subsidence of the dome to subsequent explosive eruptions (Matthews et al., 1997). Most obviously, Lascar's major April 1993 eruption follows a period in which the magnitude of emitted shortwave infrared radiation fell by 90%. At this time subsidence of the 1991–1992 lava dome was reported by field observers and this subsidence is believed to have impeded the escape of hot volatiles and ultimately triggered the eruption (Smithsonian Institution 1993a). Extrapolating beyond the period for which field observations of the summit are available, our data show that the vulcanian eruption of 20 July 1995 occurred after a period of gradual increase in short wavelength infrared flux throughout 1994 and a more rapid flux decline during 1995. We attribute this additional, otherwise undocumented, cycle of increasing and decreasing SWIR radiance as most likely representing variations in degassing through fumaroles contained within the summit crater. Alternatively, it may reflect a cycle of dome growth and decay. The explosive eruption of 17 December 1993 appears to have followed a similar, but shorter, variation in SWIR flux, and we conclude that large explosive eruptions are more likely when the 1.6-μm signal has fallen from a high to a low level. The ATSR instrument offers low-cost data at high temporal resolution. Despite the low spatial detail of the measurements, ATSR-type instruments can provide data that relate directly to the status of Lascar's lava dome and other high-temperature surfaces. We suggest that such data can therefore assist with predictions of eruptive behaviour, deduced from application of physical models of lava dome development at this and similar volcanoes. Received: 1 October 1996 / Accepted: 13 January 1997  相似文献   

20.
Crater ejecta blankets distinguished by differences in thermophysical properties from the target material were investigated in Tyrrhena Terra, Mars. Approximately one third of craters exhibit spectral differences from target material in Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Craters that exhibit these spectral differences from the target material do not strongly correlate with phyllosilicate exposures detected in near infrared data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Shock processes cannot fully explain the observed spectral trends. Rather, the subtle spectral differences observed in TES data are likely due to differences in plagioclase and/or high-silica phase abundance relative to pyroxene abundance, with the crater ejecta exhibiting lower pyroxene abundance than target materials. These mineralogic trends are consistent with several scenarios, none of which can be ruled out from existing observations: 1) vertical variations in primary lithology (considered least likely), 2) subsurface alteration exposed by impact, 3) syn- or post-impact alteration associated with the impact process, such as devitrification of melt glass materials or alteration of highly shocked materials, and 4) light surface alteration that preferentially altered/removed plagioclase and/or high-silica glass relative to pyroxene and subsequent exposure of less-altered materials from the subsurface by impact. Scenario 2 is consistent with phyllosilicate detections; Scenarios 1, 3 and 4 are consistent with CRISM phyllosilicate detections in some impact craters if phyllosilicate mineral abundance is volumetrically small. Results from this work suggest that some signatures of alteration may be escaping detection by near infrared measurements; alteration environments would be best interpreted through a combination of near infrared and thermal infrared data sets, rather than near infrared detections alone.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号