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1.
Tsunamis generated by Cascadia subduction zone earthquakes pose significant threats to coastal communities in the U.S. Pacific Northwest. Impacts of future tsunamis to individuals and communities will likely vary due to pre-event socioeconomic and demographic differences. In order to assess social vulnerability to Cascadia tsunamis, we adjust a social vulnerability index based on principal component analysis first developed by Cutter et al. (2003) to operate at the census-block level of geography and focus on community-level comparisons along the Oregon coast. The number of residents from blocks in tsunami-prone areas considered to have higher social vulnerability varies considerably among 26 Oregon cities and most are concentrated in four cities and two unincorporated areas. Variations in the number of residents from census blocks considered to have higher social vulnerability in each city do not strongly correlate with the number of residents or city assets in tsunami-prone areas. Methods presented here will help emergency managers to identify community sub-groups that are more susceptible to loss and to develop risk-reduction strategies that are tailored to local conditions.  相似文献   

2.
Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of Belgium. The basin covers about 65 km2 and the karst aquifer provides a water-supply of about 28,000 m3d-1. The methods tested were: EPIK (Doerfliger et al. 1999), DRASTIC (Aller et al. 1987), 'German method' (von Hoyer and Söfner 1998), GOD (Foster 1987) and ISIS (Civita and De Regibus 1995). The results are compared and critically examined. From the analysis, it seems that reducing the number of parameters is unsatisfactory, due to the variety of geological conditions. The various methods produce very different results at any given site. As only physically-based methods can be checked for their reliability, it is clear that future vulnerability mapping techniques must incorporate such methods.  相似文献   

3.
Social vulnerability is as much a part of risk as building damage, hazard magnitude, and economic loss. Social vulnerability refers to the capacity of a human community exposed during the impact of a natural hazard event (in this case, an earthquake) to resist, cope with, and recover from that impact. In the perspective of the 3rd millennium, we come to understand that the most efficient and accessible way to reduce the pressure of natural risks is to reduce the vulnerability level of the human communities exposed to that certain hazard. This study aims to test, in an exposed and vulnerable area, the relationship between social vulnerability and the perception of the seismic risk. The research focuses only on the first level of social vulnerability, defined as the ability of an individual within a household to recover from a natural hazard impact (Dwyer et al. 2004). A prevailing assumption was that social vulnerability influences the level of perception of the seismic risk, in an exposed, vulnerable area. To this end, two samples were used, different under the aspect of social vulnerability, in the context of the same residential area. Social vulnerability was computed as a normalized composed index that includes the poverty ratio and the demographic vulnerability ratio (depending on the age, gender, and education level indicators). The statistical processing has indicated a significant difference in the high perception level for the two samples that were compared, in the sense that in the context of an increased level of social vulnerability, people generally better acknowledge the seismic risk.
Iuliana ArmaşEmail:
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4.
Ge  Yi  Dou  Wen  Wang  Xiaotao  Chen  Yi  Zhang  Ziyuan 《Natural Hazards》2021,108(3):2629-2651

Identifying and analyzing the urban–rural differences of social vulnerability to natural hazards is imperative to ensure that urbanization develops in a way that lessens the impacts of disasters and generate building resilient livelihoods in China. Using data from the 2000 and 2010 population censuses, this study conducted an assessment of the social vulnerability index (SVI) by applying the projection pursuit cluster model. The temporal and spatial changes of social vulnerability in urban and rural areas were then examined during China’s rapid urbanization period. An index of urban–rural differences in social vulnerability (SVID) was derived, and the global and local Moran’s I of the SVID were calculated to assess the spatial variation and association between the urban and rural SVI. In order to fully determine the impacts of urbanization in relation to social vulnerability, a spatial autoregressive model and Bivariate Moran’s I between urbanization and SVI were both calculated. The urban and rural SVI both displayed a steadily decreasing trend from 2000 to 2010, although the urban SVI was always larger than the rural SVI in the same year. In 17.5% of the prefectures, the rural SVI was larger than the urban SVI in 2000, but was smaller than the urban SVI in 2010. About 12.6% of the urban areas in the prefectures became less vulnerable than rural areas over the study period, while in more than 51.73% of the prefectures the urban–rural SVI gap decreased over the same period. The SVID values in all prefectures had a significantly positive spatial autocorrelation and spatial clusters were apparent. Over time, social vulnerability to natural hazards at the prefecture-level displayed a gathering–scattering pattern across China. Though a regional variation of social vulnerability developed during China’s rapid urbanization, the overall trend was for a steady reduction in social vulnerability in both urban and rural areas.

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5.
Comprehensive hazard mitigation involves (1) understanding natural systems, (2) assessment of interactions within and between social systems and the built environment, and (3) understanding geo-spatial processes. To achieve this, local emergency managers must recognize variability in vulnerable populations exposed to hazards and develop place-based emergency plans accordingly. In this study, we assess whether cities in Los Angeles County are subject to disproportionally greater earthquake losses modeled from a M7.8 earthquake on the San Andreas fault. Furthermore, we analyze whether the variation in demographic and socioeconomic characteristics across cities is associated with the earthquake losses. We were able to explain 23.2?% of variance in economic losses by looking at the percentage of minority residents, income, and renter residents in a city [F(3,84)?=?8.47; p?<?.001]. Cities with primarily minority residents had greater economic losses when compared to cities with primarily White residents (b?=?1.01; p?<?.001). When looking at the association between demographic predictors and potential casualty rate, the percentage of Hispanic residents was positively associated with the potential casualty rate. We argue that knowledge of the relationship between earthquake hazard and the demographic characteristics of people in the area at risk is essential to mitigate the local impact from earthquakes. In other words, we apply social vulnerability assessment as part of a comprehensive risk management framework to accelerate recovery after an event. Local policy makers and the private sector can use this approach to gain a better understanding of a city??s social vulnerability and adapt their preparedness efforts accordingly.  相似文献   

6.
We assess tsunami hazards in San Diego Bay, California, using newly identified offshore tsunami sources and recently available high resolution bathymetric/topographic data. Using MOST (Titov and Synolakis, J Waterways Port Coastal Ocean Eng ASCE 124(4):57–171, 1998), we simulate locally, regionally and distant-generated tsunamis. Local tsunami source models use more realistic fault and landslide data than previous efforts. With the exception of the Alaska-Aleutian Trench, modeling results suggest that local sources are responsible for the largest waves within the San Diego Bay and Mission Bay. Because San Diego Bay is relatively well protected by North Island and the Silver Strand, the wave heights predicted are consistently smaller inside the harbor than outside. However, historical accounts, recent tsunamis and our predictions show that San Diego Bay is vulnerable to strong tsunami induced currents. More specifically, large currents are expected inside the harbor for various distant and local tsunami sources with estimated flow velocities exceeding 100 cm/s. Such currents have been damaging to harbor facilities, such as wharves and piers, and may cause boats to break from moorings and ram into adjacent harbor structures, as observed in recent historic tsunamis. More recently, following the M w 8.8 February 27, 2010 Chile earthquake, tsunami-currents damaged docks/piers in Shelter Island confirming our findings. We note that the first generation of inundation maps in use in San Diego County by emergency management was based on much larger “worst case but realistic scenarios” (Synolakis et al. 2002a), which reflected the understanding of offshore hazards pervasive ten years ago. Large inundation and overland flow depths were observed primarily in local tsunami source simulations. In particular, locally induced tsunamis appear capable to overtop the Silver Strand. The results suggest that further work needs to be carried out with respect to local tsunami sources as they seem to have worse impact in the San Diego region than previously thought but probably low probability of occurrence. We also predict that a coastal community can be devastated simultaneously by large waves inundating shores and large currents in locations with small flow depths.  相似文献   

7.
In the recent past, Australia has experienced several catastrophic hazard events and the frequency and intensity of such events is expected to increase in the future. Natural hazards can rarely be fully prevented, yet their losses can be minimized if the necessary preparedness and mitigation actions are taken before an event occurs. Identification of vulnerable groups is an important first step in any preparedness and emergency management planning process. Social vulnerability refers to population characteristics that influence the capacity of a community to prepare for, respond to and recover from disasters. Factors that contribute to social vulnerability are often hidden and difficult to capture. This study analyzes the relative levels of social vulnerability of communities at the urban?Cbush interface in the Blue Mountains and Ku-ring-gai local council areas in New South Wales (NSW), Australia. We tested whether a standardized social vulnerability index could be developed using a pre-existing set of indicators. We created an exploratory principle component analysis model using Australian Bureau of Statistics 2006 census data at the Census Collection District (CCD) level. We identified variables contributing to social vulnerability and used the component scores to develop a social vulnerability index. Finally, the social vulnerability index was mapped at the CCD level. Our results indicate that both contributors to and the level of social vulnerability differ between and within communities. In other words, they are spatially variable. They show different spatial patterns across the areas, which provides useful information for identifying communities that are most likely to experience negative disaster impacts due to their socio-demographic characteristics.  相似文献   

8.
Cian  Fabio  Giupponi  Carlo  Marconcini  Mattia 《Natural Hazards》2021,106(3):2163-2184

Climate sciences foresee a future where extreme weather events could happen with increased frequency and strength, which would in turn increase risks of floods (i.e. the main source of losses in the world). The Mediterranean basin is considered a hot spot in terms of climate vulnerability and risk. The expected impacts of those events are exacerbated by land-use change and, in particular, by urban growth which increases soil sealing and, hence, water runoff. The ultimate consequence would be an increase of fatalities and injuries, but also of economic losses in urban areas, commercial and productive sites, infrastructures and agriculture. Flood damages have different magnitudes depending on the economic value of the exposed assets and on level of physical contact with the hazard. This work aims at proposing a methodology, easily customizable by experts’ elicitation, able to quantify and map the social component of vulnerability through the integration of earth observation (EO) and census data with the aim of allowing for a multi-temporal spatial assessment. Firstly, data on employment, properties and education are used for assessing the adaptive capacity of the society to increase resilience to adverse events, whereas, secondly, coping capacity, i.e. the capacities to deal with events during their manifestation, is mapped by aggregating demographic and socio-economic data, urban growth analysis and memory on past events. Thirdly, the physical dimension of exposed assets (susceptibility) is assessed by combining building properties acquired by census data and land-surface characteristics derived from EO data. Finally, the three components (i.e. adaptive and coping capacity and susceptibility) are aggregated for calculating the dynamic flood vulnerability index (FVI). The approach has been applied to Northeast Italy, a region frequently hit by floods, which has experienced a significant urban and economic development in the past decades, thus making the dynamic study of FVI particularly relevant. The analysis has been carried out from 1991 to 2016 at a 5-year steps, showing how the integration of different data sources allows to produce a dynamic assessment of vulnerability, which can be very relevant for planning in support of climate change adaptation and disaster risk reduction.

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9.
The spatial distribution and several morphometric characteristics of the Quaternary alluvial fans of the San Juan River, in the province of San Juan, at the Central and Western part of Argentina, have been studied to classify them as paraglacial megafans, as well to ratify its depositional environmental conditions. The high sedimentary load exported by San Juan river from the Central Andes to the foreland depressions is estimated about 3,682,200 hm3. The large alluvial fans of Ullum-Zonda and Tulum valleys were deposited into deep tectonic depressions, during the Upper Pleistocene deglaciation stages. The outcome of collecting remotely sensed data, map and DEM data, geophysical data and much fieldwork gave access to morphometric, morphographic and morphogenetic data of these alluvial fans. The main drainage network was mapped on processed images using QGis (vers.2.0.1). Several fan morphometric parameters were measured, such as the size, the shape, the thickness, the surface areas and the sedimentary volume of exported load. The analyzed fans were accumulated in deep tectonic depressions, where the alluvium fill reaches 700 to 1200 m thick. Such fans do not reach the large size that other world megafans have, and this is due to tectonic obstacles, although the sedimentary fill average volume surpasses 514,000 hm3. The author proposes to consider Ullum-Zonda and Tulum alluvial fans as paraglacial megafans. According to the stratigraphic relationships of the tropical South American Rivers, the author considers that the San Juan paraglacial megafans would have occurred in the period before 24 ka BP, possibly corresponding to Middle Pleniglacial (ca 65–24ka BP). They record colder and more humid conditions compared with the present arid and dry conditions.  相似文献   

10.
Climate change,environmental degradation and migration   总被引：1，自引：0，他引：1  
Climate change will have a progressively increasing impact on environmental degradation and environmentally dependent socio-economic systems with potential to cause substantial population displacement. The key concerns in Less Developed Countries (LDCs) will include serious threats to food security and health, considerable economic decline, inundation of coastal areas, and degradation of land and fresh water resources (Reuveny in Polit Geogr, 2007). The relationship between environmental change and potential humanitarian crises has been captured by: McGregor (Geography and refugees: patterns and processes of change, Belhaven Press, London, pp 159–70, 1993), Kibreab (Environment and Population Change, International Union for the Scientific Study of Population, Liège, 1994), Kibreab (Disasters 21(1):20–38, 1997), Myers (Bioscience 43:752–761, 1993), Myers and Kent (Environmental exodus: an emergent crisis in the global arena, Climate Institute, Washington, DC, 1995), Black (New Issues in Refugee Research, Working Paper no. 34, 2001), Lee (Environmental matters: conflict, refugees and international relations, World Human Development Institute Press, Seoul and Tokyo, 2001), Castles (Environmental Change and Induced Migration: Making Sense of the Debate Working Paper No. 70, 2002), Christian Aid (Human tide: the real migration crisis, Christian Aid, London, 2007), and Massey et al. (, 2007). However, we know little about the interplay between environmental change and stresses on ecological systems, resulting socio-economic vulnerability and potential outcomes in terms of population displacement or induced migration. So far these relationships are poorly conceptualized, lack systematic investigation, and are reduced to simplistic causal explanations. This leads to misleading conclusions that deny the complex multivariate processes—environmental, political, social, and economic— which are the root causes of environmentally induced migration and/or conflict. When people are faced with severe environmental degradation they have one of three options: (1) stay and adapt to mitigate the effects; (2) stay, do nothing and accept a lower quality of life; or (3) leave the affected area. The process of movement and migration is usually subject to a complex set of push and pull forces, where push forces relate to the source area while pull factors relate to the destination. These forces are in constant flux, as much as environmental change, and interact with socio-economic and political conditions including state or government decision making powers, which can tip the balance at any point by either denying movement or the right to settle elsewhere. The paper focuses on how environmental change and environmental hazards contribute to the migration by exploring the mechanisms through which vulnerability and migration are linked—via livelihoods, relocation policies, and other factors. The paper begins by outlining important definitions of what is environmentally induced migration. The paper also considers the question of whether migration is a process that reduces or increases vulnerability. The paper draws on multidisciplinary literature including ecology, environment, and climate change; sociology of migration; anthropology of displacement; and economics; but also on preliminary from various case studies in Egypt, Vietnam, and Mozambique.  相似文献   

11.
Previous research on the prehistoric communities of Chaco Canyon, New Mexico (ca. A.D. 800–1250) provides evidence of an extensive procurement system of nonlocal food and economic goods. In this paper, we use oxygen and strontium isotope analyses to establish whether animal protein followed a similar pattern. We contextualized our isotopic analyses of the archaeofaunas from recent excavations at Pueblo Bonito with data on modern faunas across an area of approximately 100,000 km2 around the site. Our results show that most archaeological deer, rabbits, and prairie dogs were obtained from >40 km away from Pueblo Bonito with the latter two likely being garden hunted. The Chuska Mountains west of Chaco Canyon and more distant San Juan Mountains to the north were the main source areas. These results closely align with previous results on architectural wood, corn, and other key resources. The importation of small game animals suggests that the local supplies could not meet the needs of the community. Long‐distance meat procurement may have been embedded within a more complex network of ritual‐goods exchange or tribute that helped to offset the transport costs. Resource depletion may have contributed to the eventual abandonment of the region during the Medieval Warm Period.  相似文献   

12.
The San Juan River, located in San Juan Province (Argentina), crosses the Precordillera and other geologic units including the Ullum tectonic valley and the La Laja Zone between latitudes 31°S and 32°S. The San Juan River is antecedent as is suggested by its two perpendicular segments linked by an almost parallel segment to the main structural trend. Along the Precordillera, the San Juan River valley has many different alluvial fans at the river junctions with its tributaries. The Quaternary alluvial fans display surfaces cut in a series of steps which we consider to be alluvial terraces generated by aggradation and repeated incision episodes. The studied sector includes one area with recent major seismic activity (La Laja Zone), another without major seismic activity (Precordillera area), and a subsident area (Ullum area) where a large lake was formed 6500 yr BP. The old San Juan River was captured by the Quebrada de Ullum valley by means of a 25-m incision, which resulted in river-gradient headward erosion. The San Juan River gradient shows some irregularities that, although unrelated to the main structures, are associated with river dynamics, which emphasizes lithologic differences. The main river valley width, the geometry and gradient of each tributary, together with the basement rock lithologies and the size of each local source area are the major factors which control the alluvial terrace generation processes. In the La Laja Zone, where the uppermost terrace is capped by travertine, dating of travertine deposits suggests that the maximum incision rate is 0.9–1 mm/yr related to episodic activity on the La Laja Fault.  相似文献   

13.
King  David 《Natural Hazards》2001,24(2):147-156
Advances in computer technology have made very large databases easily accessible to users and managers. The census and land databases are of enormous use to hazard managers and planners. An extensive literature has identified groups of social, economic and demographic indicators that may be combined with physical and land data to predict and categorise levels of community vulnerability. Impact scenario mapping can be very precise and impressive in its detail, but a range of constraints, such as ageing of the data, the arbitrary nature of boundaries, problems of weighting indicators, and categorisation of vulnerability, impose limitations on the use of socioeconomic indicators to predict community vulnerability.  相似文献   

14.
Previous radiocarbon ages of detrital moss fragments in basal organic sediments of Lake Emma indicated that extensive deglaciation of the San Juan Mountains occurred prior to 14,900 yr B.P. (Carrara et al., 1984). Paleoecological analyses of insect and plant macrofossils from these basal sediments cast doubt on the reliability of the radiocarbon ages. Subsequent accelerator radiocarbon dates of insect fossils and wood fragments indicate an early Holocene age, rather than a late Pleistocene age, for the basal sediments of Lake Emma. These new radiocarbon ages suggest that by at least 10,000 yr B.P. deglaciation of the San Juan Mountains was complete. The insect and plant macrofossils from the basal organic sediments indicate a higher-than-present treeline during the early Holocene. The insect assemblages consisted of about 30% bark beetles, which contrasts markedly with the composition of insects from modern lake sediments and modern specimens collected in the Lake Emma cirque, in which bark beetles comprise only about 3% of the assemblages. In addition, in the fossil assemblages there were a number of flightless insect species (not subject to upslope transport by wind) indicative of coniferous forest environments. These insects were likewise absent in the modern assemblage.  相似文献   

15.
Perception of flood risk in Danube Delta,Romania   总被引：1，自引：1，他引：0  
For exposed and vulnerable communities, the perception of natural risk is an essential link in the analysis of man–environment coping relationship and also an important parameter in the quantification of complex vulnerability as a central predictive variable in the risk equation. The topic of flood risk in related perception is of considerable interest, as some recently published papers have proven (Messner and Meyer 2005, 2006; Raaijmakers et al. 2008). The aim of the current study is to reveal the conscious and unconscious attitudes towards the flood risk for the inhabitants of the Danube Delta/Romania. These attitudes, defined by different degrees of psychological vulnerability, represent the background for a series of psycho-behavioural patterns that generate certain adjustment mechanisms and strategies. Application of a specially designed questionnaire and the statistical analysis of the results revealed two psychological factors as essential in establishing the psychosocial vulnerability degree of the interviewed subjects: (i) an internal control factor and (ii) an external control factor. The persons characterized by inner control have a significantly reduced general anxiety level in comparison to individuals with the control factor placed externally. As confidence diminishes, it increases the tendency of the individual to rely on the external factors for support and security. The lack of resources (indicating lower resilience) and mistrust in the support given emphasizes non-adaptive behaviours.
Iuliana ArmaşEmail:
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16.
The comment by Day et al. (Contrib Mineral Petrol, 2012) (1) discusses the validity of the previously obtained oxygen isotope data for El Hierro and La Palma (Canary Island) olivines, (2) questions the approach by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) of using weakly correlated variations of δ18Oolivine values with X px (proportion of pyroxenite-derived melt in the parental magma), and (3) provides reasons why oxygen isotope data by secondary ion mass spectrometry (SIMS) “offer sensitive means for detecting melt-crust interactions.” We respond these comments and report a new set of oxygen isotope measurements performed by SIMS and single-grain laser fluorination methods. These measurements confirm our previous data and conclusions and demonstrate the ability of the SIMS technique to analyze O isotopes in terrestrial samples with 2-sigma uncertainty better than ±0.25 ‰.  相似文献   

17.
The increase in the frequency and magnitude of disasters triggered by earthquakes in different regions of the Earth is a major challenge to contemporary societies. The awareness that disasters and risk are processes structured on spatial?Ctemporal interactions maintained at the social-ecological system between the natural hazards and the vulnerabilities of socioeconomic, political and physical nature becomes utterly important in the increase of social systems?? resilience. Thus, the assessment of social vulnerability plays a decisive role in understanding the factors that distinguishes individuals, households and communities, in terms of their ability to anticipate, cope with, resist to and recover from the impact of disasters triggered by natural hazards. This article presents a geographic information system (GIS)-based approach model to assess the social vulnerability to seismic risk using multicriteria analysis (MCA) techniques, in a group decision-making process. The methodology applied to the municipality of Vila Franca do Campo (S?o Miguel Island, Azores, Portugal) identified moderate social vulnerability values at the neighbourhood level and higher social vulnerability values for the built environment and demographic characteristics of the social groups. The social vulnerability patterns make a clear distinction between the older/historical urban cores and the new urban areas. In the first case, the presence of ancient buildings constructed with materials of low resistance to earthquakes coupled with a higher population density and the traits of demographic and socioeconomic frailties of the social groups, results in higher vulnerability values. This pattern is common in the historic centre of S. Miguel district, Ribeira das Taínhas, northern areas of água de Alto and western and eastern neighbourhoods of Ponta Gar?a. The new urban areas, mainly found in S. Pedro, central areas of água de Alto, S. Miguel and Ponta Gar?a districts, have lower values of social vulnerability due to changes in the built, demographic and socioeconomic environments. Results recommend the integration of social vulnerability indexes into seismic risk mitigation policies and emergency management planning.  相似文献   

18.
The frequency of natural disasters and the extent of their consequences at a global level are constantly increasing. This trend is partially caused by increased population vulnerability, which implies the degree of population vulnerability due to high-magnitude natural processes. This paper presents an analysis of vulnerability to natural disaster in Serbia in the second half of the twentieth and the early twenty-first century. Vulnerability changes were traced on the basis of demographic–economic indicators derived from statistical data for local government units (municipalities) provided by the Statistical Office of the Republic of Serbia. Calculations were performed in the geographical information system environment. The results of the study show that spatial and temporal vulnerability variations are causally correlated with changes in the selected components. Significant rise of vulnerability is related to urban areas, while lower values are characteristic for other areas of Serbia; this is primarily a consequence of different population density.  相似文献   

19.
In this paper, the extent to which the potentially transit-dependent portion of the population is vulnerable to the effects of a hurricane is estimated. The vulnerability of an area is defined as a composite measure of the proportion of disadvantaged persons, distance to transit, and flooding potential of people within an area. Unlike past studies which have focused on the vulnerability of the population in relatively large geographic areas, this study estimates the vulnerability of the population in 30 m × 30 m areas as defined in the National Land Cover Database. Population estimates from the national census at block level are disaggregated to the 30 m × 30 m units using a modified dasymetric mapping method in ArcGIS. The modified mapping method assigns population to each small areal unit using weights estimated by regressing the area of each land use in a census block against the population in that block. The coefficients in the regression analysis are “weights” associating population with each land use, and are used to distribute the population in each census block to the small geographic units based on their land use. In a case study of New Orleans, the results show that some areas are not well served by the existing transit pickup locations, as evidenced by their high vulnerability scores. Reassignment of pickup point locations to cover higher vulnerability score areas was investigated using integer linear programming. The results show that the optimally located pickup points serve areas with a larger average vulnerability score than the current pickup points in the study area. The method appears to be helpful in identifying vulnerable areas that, subsequently, could receive improved hurricane evacuation service in the future.  相似文献   

20.
Locally, voluminous andesitic volcanism both preceded and followedlarge eruptions of silicic ash-flow tuff from many calderasin the San Juan volcanic field. The most voluminous post-collapselava suite of the central San Juan caldera cluster is the 28Ma Huerto Andesite, a diverse assemblage erupted from at least5–6 volcanic centres that were active around the southernmargins of the La Garita caldera shortly after eruption of theFish Canyon Tuff. These andesitic centres are inferred, in part,to represent eruptions of magma that ponded and differentiatedwithin the crust below the La Garita caldera, thereby providingthe thermal energy necessary for rejuvenation and remobilizationof the Fish Canyon magma body. The multiple Huerto eruptivecentres produced two magmatic series that differ in phenocrystmineralogy (hydrous vs anhydrous assemblages), whole-rock majorand trace element chemistry and isotopic compositions. Hornblende-bearinglavas from three volcanic centres located close to the southeasternmargin of the La Garita caldera (Eagle Mountain–FourmileCreek, West Fork of the San Juan River, Table Mountain) definea high-K calc-alkaline series (57–65 wt % SiO2) that isoxidized, hydrous and sulphur rich. Trachyandesitic lavas fromwidely separated centres at Baldy Mountain–Red Lake (westernmargin), Sugarloaf Mountain (southern margin) and Ribbon Mesa(20 km east of the La Garita caldera) are mutually indistinguishable(55–61 wt % SiO2); they are characterized by higher andmore variable concentrations of alkalis and many incompatibletrace elements (e.g. Zr, Nb, heavy rare earth elements), andthey contain anhydrous phenocryst assemblages (including olivine).These mildly alkaline magmas were less water rich and oxidizedthan the hornblende-bearing calc-alkaline suite. The same distinctionscharacterize the voluminous precaldera andesitic lavas of theConejos Formation, indicating that these contrasting suitesare long-term manifestations of San Juan volcanism. The favouredmodel for their origin involves contrasting ascent paths anddifferentiation histories through crustal columns with differentthermal and density gradients. Magmas ascending into the mainfocus of the La Garita caldera were impeded, and they evolvedat greater depths, retaining more of their primary volatileload. This model is supported by systematic differences in isotopiccompositions suggestive of crust–magma interactions withcontrasting lithologies. KEY WORDS: alkaline; calc-alkaline; petrogenesis; episodic magmatism; Fish Canyon system  相似文献   

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