Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in thr...Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.展开更多
This work assessed the impact of land use and land cover (LULC) change on the socio-economic conditions of the inhabitants in the Mount Bambouto Caldera from 1980-2016. To achieve this, three time series satellite ima...This work assessed the impact of land use and land cover (LULC) change on the socio-economic conditions of the inhabitants in the Mount Bambouto Caldera from 1980-2016. To achieve this, three time series satellite images;Landsat Thematic Mapper (TM) (1980), Landsat Enhanced Thematic Mapper (ETM) (2001), and Landsat 8 Operational Land Imager (OLI) (2016) scenes were employed to investigate the changes in LULC. The use of satellite images was supplemented with individual interviews, discussions with focus groups and key informants, and direct field observations. Five categories of LULC classes were identified namely: thick woody vegetation (natural forest and oil palms), light vegetation (croplands), savannah (grasslands), buildings (settlements), and bare grounds. The results showed that between 1980 and 2016, croplands, buildings and bare lands increased by 4%, 0.43% and 5.7% respectively while savannah/grassland and natural forest decreased by 4.4% and 5.8% respectively. Household survey revealed soil fertility decline and lack of credit schemes to be major constraints to crop production. Many religious holidays contribute to seasonal food shortages and the community faces a host of socio-economic and institutional challenges. Consequently, majority of house-holds are destitute, live in abject poverty;which is an indication of the need for interventions by government and other development stakeholders to tackle the problems of soil fertility, land use change and food insecurity.展开更多
Objective As the world＇s third largest volcanic type uranium ore field,the Xiangshan volcanic basin has attracted much attention for its large industrial value.The ore hosting rocks are mainly the early Cretaceous rh...Objective As the world＇s third largest volcanic type uranium ore field,the Xiangshan volcanic basin has attracted much attention for its large industrial value.The ore hosting rocks are mainly the early Cretaceous rhyodacite and porphyroclastic lava,as well as small amounts of high level intrusive acidic rocks and metamorphic rocks.展开更多
Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line,built between 21 Ma and 4.5 Ma(Nkouathio et al.,2008).It is situated at about 200 km NE of mount Cameroon,at 09°55′and 10°15′East a...Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line,built between 21 Ma and 4.5 Ma(Nkouathio et al.,2008).It is situated at about 200 km NE of mount Cameroon,at 09°55′and 10°15′East and,05°25′and 05°50′North.This volcano covers an area of 500 Km^2 and culminates at 2740 m at Meletan hill and bears a collapsed elliptical caldera at the summit(13×8 km).Mount展开更多
We analyze the crustal rheology beneath the active resurgent Campi Flegrei caldera(CFc) in Southern Italy by modelling the 3 D brittle-ductile(B/D) transition, based on available thermal, geological and geophysical da...We analyze the crustal rheology beneath the active resurgent Campi Flegrei caldera(CFc) in Southern Italy by modelling the 3 D brittle-ductile(B/D) transition, based on available thermal, geological and geophysical data. Firstly, the thermal field in the conductive physical regime is modeled using a finite element method; based on an optimization tool, this method is applied to evaluate the location and dimensions of the deep thermal source beneath the caldera. A horizontally-extended thermal anomaly located at about 5000 m depth below sea level is identified beneath Pozzuoli Bay, a part of the CFc. The same isotherm is located at a depth of 20,000 m beyond the caldera. This indicates a higher horizontal temperature gradient in the caldera with respect to the surrounding area. Next, we utilize this thermal model to image the 3D rheological stratification of the shallow crust below the caldera with two different values of strain rates. Within the caldera, the B/D transitions with ε equal to 10^(-12) s^(-1) and 10^(-8) s^(-1) are located at 3000 m and 5000 m depths, respectively. Outside the caldera, the transition is very deep(15,000-20,000 m), seemingly uninfluenced by the thermal state of the CFc volcanism. Finally, we compare these results with the spatial distribution of earthquake hypocenters, Benioff strain release and b-value distribution to investigate the relationship between crustal rheology and seismicity characteristics. Our analysis reveals that the image of the B/D transition is in agreement with the distribution of earthquake hypocenters, constraining the potential seismogenic volume of the region. Our study demonstrates that knowledge of the rheological state of a volcanic system is an important element to interpret its dynamic, forecast future activity and improve evaluation of the associated seismic hazard.展开更多
Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line, built between 21 Ma and 4.5 Ma. It is situated approximately 200 km NE of Mount Cameroon, between 09° 55＇ and 10°15＇ longitude eas...Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line, built between 21 Ma and 4.5 Ma. It is situated approximately 200 km NE of Mount Cameroon, between 09° 55＇ and 10°15＇ longitude east and, 05°25＇ and 05°50＇ latitude north. The volcano covers an area of 500 km^2 and culminates at 2740 m at Meletan dome and bears a collapsed caldera at the summit （13 × 8 km）. Mount Bambouto is characterized by several natural hazards of different origins： meteorological, such as landslides and rock falls; anthropogenic, such as bushfires, tribal wars and deforestation; and volcanological, such as volcanic eruption. The thematic map shows that 55-60% of the caldera has high probability of occurrence of mass movement. The caldera has a high population density （3000 inhabitants）, which increases the level of risk, evaluated at approximately $US3.8 million for patrimony, 3000 civilian deaths and destruction of biodiversity.展开更多
This study considers the restoration of the plant cover destroyed by a catastrophic volcano eruption in the south of Kamchatka Peninsula(the Ksudach caldera,Shtyubel cone),with a particular attention to the role of wo...This study considers the restoration of the plant cover destroyed by a catastrophic volcano eruption in the south of Kamchatka Peninsula(the Ksudach caldera,Shtyubel cone),with a particular attention to the role of woody plants.It aims to qualitatively estimate(at a qualitative level)the rate of the primary succession development depending on the microrelief and the modern relief-forming processes.The vegetation recovery in the caldera after the Shtyubel cone eruption 109 years ago proceeds slowly and irregularly.It proceeds most slowly on a thick tephra mantle continuously disturbed by water and wind erosion,lahars,debris flows,landslides,etc.Such conditions are most typical of the western part of the caldera dominated by pumice fields with occasional patches of pioneer herbs and dwarf shrubs.Alpine tundra communities with gradually expanding patches of shrub alder develop in the southern,eastern and northeastern parts of the Ksudach caldera.Since 1997 the area of the shrub alder communities has increased by 1.9 times,while the alpine tundra–by 1.3 times only.The woody plants(dwarf shrubs and prostrate shrubs)are of particular importance in the process of the vegetation recovery on pumice fields.We suggest that the bark thickness of woody plants is an integrated indicator,which may serve for estimating the state of ecosystem in the course of the primary succession development on juvenile sediments.The extremely inhospitable environments cause changes in physiological processes in the plant body and in its bark in particular.The results show that woody plants have a"thin"bark and develop some structural-functional arrangements for keeping bark tissues at their minimum.So,the woody plant structure and the rate of changes in plant communities are under control of the geomorphic conditions and primarily–of physicochemical features of the pyroclastic cover.展开更多
The Bamenda Volcano (BV) (2621 m) is a stratovolcano situated in the Cameroon Line (CL). BV includes Mount Lefo (2534 m) which is situated on its southern slopes and contains one elliptical caldera (3 × 4 km). Th...The Bamenda Volcano (BV) (2621 m) is a stratovolcano situated in the Cameroon Line (CL). BV includes Mount Lefo (2534 m) which is situated on its southern slopes and contains one elliptical caldera (3 × 4 km). This caldera is propitious to farming and breeding activity. Despite these profitable assets, Lefo caldera (LC) is an amphitheater of the occurrence of multi-origin hazards that have direct or indirect impacts on the biodiversity and human patrimony. The most present hazards are those of meteorological origin. Numerous combined factors (steepest slopes, heavy rainfalls, weathered state of volcanic products…) rule these hazards. These factors gave rise to the occurrence of landslides, gullies erosion and rock falls which occur precisely on caldera northern and eastern rims. Hazards of anthropogenic origin are based on the destruction of the vegetation cover by the population for dealing, firewood and building issues. Moreover, during the breeding activity, the cattle covers the caldera throughout the day;this unevens the topography and destroys the meadow. Hazards of volcanological origin are not yet occurring in LC;but the recent Lake Monoun (1984) and Nyos (1986) CO2 eruptions, mount Cameroon eruptions (1999 and 2000) and mount Oku Lake event (2011) which are close to the BV and, the age of 0 Myr of basalt, constitutes a subject of controversy toward the reactivation of the Cameroonian hotspot faults. The assessment of risks in LC was based on the average income of breeding activity and house investment. The economy of LC is valued at about US$527472.527. The level of such risk will be important in case of loss of human beings and the destruction of geomorphosites’ values. In order to reduce the level of looses in this zone, hazard and risks maps are provided in this paper as well as some recommendations.展开更多
<p align="justify"> <span style="font-family:Verdana;"></span><span style="font-family:Verdana;"></span>Soil organic carbon (SOC) mineralization was carried ...<p align="justify"> <span style="font-family:Verdana;"></span><span style="font-family:Verdana;"></span>Soil organic carbon (SOC) mineralization was carried out on soil samples collected from two depths: 0 - 20 cm and 20 - 40 cm for all land use (LU) types (grasslands, croplands, natural forest/fallow lands, cocoa/palm plantations, and settlement/agro-forests). Microbiological analyses were carried out by measuring microbial activity in 40 g of dried soil samples wetted to 60% water holding capacity and incubated at 27 °C. Carbon dioxide (CO<sub>2</sub>) emission was measured for 10 weeks using a CO<sub>2</sub> trap. Descriptive and graphical analyses of CO<sub>2</sub> respiration were done using CO<sub>2 </sub>emission data. Models were developed to describe CO<sub>2</sub> respiration and the first order kinetic model provided best fit to C-mineralization. Potentially mineralizable carbon (C<sub>o</sub>) and C-mineralization rate were higher in grasslands than other LU types, indicating a higher rate of microbial activity and carbon cycling. Metabolic quotient was higher in forest/fallow lands and reflects greater stress of the microbial community and a high requirement of maintenance energy. Grasslands enhanced more SOC accumulation and decomposition, suggesting a better carbon sink than other land use and management systems (LUMS). Microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) varied across LU patterns with maximum values in grasslands and minimum values in natural forest/fallow lands insinuating better soil quality for grasslands. MBC and SOC positively correlated with C<sub>o</sub> and C-mineralization, which intimates that C-mineralization is influenced by availability of MBC and SOC. Metabolic quotient (qCO<sub>2</sub>) negatively correlated with microbial quotient (MBC:SOC), depicting that higher values of qCO<sub>2</sub> signify difficulties in using organic substrates during microbial activity as a result of low MBC:SOC. Changes in LUMS affected the mineralization kinetics of SOC in the study area. </p>展开更多
The study on empowerment strategies for tourism sustainability was carried out in 16 geosites located in seven regencies. These include Karo, Dairi, Simalungun, Samosir, Toba Samosir, North Tapanuli, and Humbang Hasun...The study on empowerment strategies for tourism sustainability was carried out in 16 geosites located in seven regencies. These include Karo, Dairi, Simalungun, Samosir, Toba Samosir, North Tapanuli, and Humbang Hasundutan, in Toba Caldera Region (TCA), North Sumatra Province. The empowerment strategies will enhance local and national tourism development policy directives, boost development geared towards community tourism interests, and achieve GGN directives according to the concepts outlined by UNESCO. This geotourism development has been formulated through a synthesis of various investigations including the analyses of government references, potential tourist attractions, and SWOT. Furthermore, the SWOT analysis showed that a travel plan combining the elements of cultural heritage and geosites is an alternative empowerment for sustainable regional development through geotourism, using Pusuk Bukit as a pilot area. Geosites have been mapped as the basis for Toba Caldera’s development.展开更多
Clay-type Li deposits are poised to play a pivotal role in addressing the surging global demand for Li.The McDermitt clay-type Li deposit,located in Nevada,is the largest Li deposit in the United States,with Li hosted...Clay-type Li deposits are poised to play a pivotal role in addressing the surging global demand for Li.The McDermitt clay-type Li deposit,located in Nevada,is the largest Li deposit in the United States,with Li hosted by a clay-rich sequence of smectite-dominated intervals and illite-dominated intervals,respectively.However,the occurrence of Li and the genesis of Li-bearing minerals within smectite-dominated intervals have not been thoroughly investigated in previous research.Here,we studied the mineralogy,the in-situ Li distribution,and the bonding environments of Li within the smectite intervals using a combination of instru-mental techniques including scanning electron microscope,transmission electron microscope,time-of-flight secondary ion mass spectrometry,and nuclear magnetic resonance.Our results indicate that the smectite exhibits low crystallinity characteristics of lacustrine clay authigenesis and is com-monly found tofill the interstices among volcanic minerals or envelop them;Li is mainly hosted by Mg-smectite rather than the volcanic minerals.Within the tuffaceous sediment samples,the volcanic glass has undergone a transformation,resulting in its complete disappearance and alteration into clay minerals.Owing to the octahedral sites of Mg-smectite bounded in Li,it is referred to be hectorite.We interpret that the hectorite’s precipitation occurs in a high saline-alkaline water environment,a result of McDermitt tuffdissolution.This conclusion can be supported by the coexistence of spherulitic calcite and hectorite.Overall,this study confirms hectorite as the main Li-bearing mineral and increases the understanding of the genetic model of hectorite formation in intracontinental caldera basins.展开更多
基金funded by the National Natural Science Foundation of China under Grant Nos.41972313 and 41790453by the Engineering Research Center of Geothermal Resources Development Technology and Equipment,Ministry of Education,Jilin University,China.
文摘Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.
文摘This work assessed the impact of land use and land cover (LULC) change on the socio-economic conditions of the inhabitants in the Mount Bambouto Caldera from 1980-2016. To achieve this, three time series satellite images;Landsat Thematic Mapper (TM) (1980), Landsat Enhanced Thematic Mapper (ETM) (2001), and Landsat 8 Operational Land Imager (OLI) (2016) scenes were employed to investigate the changes in LULC. The use of satellite images was supplemented with individual interviews, discussions with focus groups and key informants, and direct field observations. Five categories of LULC classes were identified namely: thick woody vegetation (natural forest and oil palms), light vegetation (croplands), savannah (grasslands), buildings (settlements), and bare grounds. The results showed that between 1980 and 2016, croplands, buildings and bare lands increased by 4%, 0.43% and 5.7% respectively while savannah/grassland and natural forest decreased by 4.4% and 5.8% respectively. Household survey revealed soil fertility decline and lack of credit schemes to be major constraints to crop production. Many religious holidays contribute to seasonal food shortages and the community faces a host of socio-economic and institutional challenges. Consequently, majority of house-holds are destitute, live in abject poverty;which is an indication of the need for interventions by government and other development stakeholders to tackle the problems of soil fertility, land use change and food insecurity.
基金financially supported by National Natural Science Foundation of China (grant No.41572185)
文摘Objective As the world＇s third largest volcanic type uranium ore field,the Xiangshan volcanic basin has attracted much attention for its large industrial value.The ore hosting rocks are mainly the early Cretaceous rhyodacite and porphyroclastic lava,as well as small amounts of high level intrusive acidic rocks and metamorphic rocks.
文摘Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line,built between 21 Ma and 4.5 Ma(Nkouathio et al.,2008).It is situated at about 200 km NE of mount Cameroon,at 09°55′and 10°15′East and,05°25′and 05°50′North.This volcano covers an area of 500 Km^2 and culminates at 2740 m at Meletan hill and bears a collapsed elliptical caldera at the summit(13×8 km).Mount
基金carried out within the framework of the GEOTHERMAL ATLAS OF SOUTHERN ITALY project, one of six constituting the program CNR per il Mezzogiorno of the Italian National Research Councilpartially funded by 368 DTA. AD004.065.001 Geophysics e Project CNR _PDGP 20162018
文摘We analyze the crustal rheology beneath the active resurgent Campi Flegrei caldera(CFc) in Southern Italy by modelling the 3 D brittle-ductile(B/D) transition, based on available thermal, geological and geophysical data. Firstly, the thermal field in the conductive physical regime is modeled using a finite element method; based on an optimization tool, this method is applied to evaluate the location and dimensions of the deep thermal source beneath the caldera. A horizontally-extended thermal anomaly located at about 5000 m depth below sea level is identified beneath Pozzuoli Bay, a part of the CFc. The same isotherm is located at a depth of 20,000 m beyond the caldera. This indicates a higher horizontal temperature gradient in the caldera with respect to the surrounding area. Next, we utilize this thermal model to image the 3D rheological stratification of the shallow crust below the caldera with two different values of strain rates. Within the caldera, the B/D transitions with ε equal to 10^(-12) s^(-1) and 10^(-8) s^(-1) are located at 3000 m and 5000 m depths, respectively. Outside the caldera, the transition is very deep(15,000-20,000 m), seemingly uninfluenced by the thermal state of the CFc volcanism. Finally, we compare these results with the spatial distribution of earthquake hypocenters, Benioff strain release and b-value distribution to investigate the relationship between crustal rheology and seismicity characteristics. Our analysis reveals that the image of the B/D transition is in agreement with the distribution of earthquake hypocenters, constraining the potential seismogenic volume of the region. Our study demonstrates that knowledge of the rheological state of a volcanic system is an important element to interpret its dynamic, forecast future activity and improve evaluation of the associated seismic hazard.
文摘Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line, built between 21 Ma and 4.5 Ma. It is situated approximately 200 km NE of Mount Cameroon, between 09° 55＇ and 10°15＇ longitude east and, 05°25＇ and 05°50＇ latitude north. The volcano covers an area of 500 km^2 and culminates at 2740 m at Meletan dome and bears a collapsed caldera at the summit （13 × 8 km）. Mount Bambouto is characterized by several natural hazards of different origins： meteorological, such as landslides and rock falls; anthropogenic, such as bushfires, tribal wars and deforestation; and volcanological, such as volcanic eruption. The thematic map shows that 55-60% of the caldera has high probability of occurrence of mass movement. The caldera has a high population density （3000 inhabitants）, which increases the level of risk, evaluated at approximately $US3.8 million for patrimony, 3000 civilian deaths and destruction of biodiversity.
基金supported by the Russian Foundation for Basic Research(Grant RFBR No.15-04-04774)and within the framework of the state contract with the Space Systems Research Institute(Roskosmos)under the"Monitoring-SG"programsupported financially by RFBR(Grant№18-0500967)。
文摘This study considers the restoration of the plant cover destroyed by a catastrophic volcano eruption in the south of Kamchatka Peninsula(the Ksudach caldera,Shtyubel cone),with a particular attention to the role of woody plants.It aims to qualitatively estimate(at a qualitative level)the rate of the primary succession development depending on the microrelief and the modern relief-forming processes.The vegetation recovery in the caldera after the Shtyubel cone eruption 109 years ago proceeds slowly and irregularly.It proceeds most slowly on a thick tephra mantle continuously disturbed by water and wind erosion,lahars,debris flows,landslides,etc.Such conditions are most typical of the western part of the caldera dominated by pumice fields with occasional patches of pioneer herbs and dwarf shrubs.Alpine tundra communities with gradually expanding patches of shrub alder develop in the southern,eastern and northeastern parts of the Ksudach caldera.Since 1997 the area of the shrub alder communities has increased by 1.9 times,while the alpine tundra–by 1.3 times only.The woody plants(dwarf shrubs and prostrate shrubs)are of particular importance in the process of the vegetation recovery on pumice fields.We suggest that the bark thickness of woody plants is an integrated indicator,which may serve for estimating the state of ecosystem in the course of the primary succession development on juvenile sediments.The extremely inhospitable environments cause changes in physiological processes in the plant body and in its bark in particular.The results show that woody plants have a"thin"bark and develop some structural-functional arrangements for keeping bark tissues at their minimum.So,the woody plant structure and the rate of changes in plant communities are under control of the geomorphic conditions and primarily–of physicochemical features of the pyroclastic cover.
文摘The Bamenda Volcano (BV) (2621 m) is a stratovolcano situated in the Cameroon Line (CL). BV includes Mount Lefo (2534 m) which is situated on its southern slopes and contains one elliptical caldera (3 × 4 km). This caldera is propitious to farming and breeding activity. Despite these profitable assets, Lefo caldera (LC) is an amphitheater of the occurrence of multi-origin hazards that have direct or indirect impacts on the biodiversity and human patrimony. The most present hazards are those of meteorological origin. Numerous combined factors (steepest slopes, heavy rainfalls, weathered state of volcanic products…) rule these hazards. These factors gave rise to the occurrence of landslides, gullies erosion and rock falls which occur precisely on caldera northern and eastern rims. Hazards of anthropogenic origin are based on the destruction of the vegetation cover by the population for dealing, firewood and building issues. Moreover, during the breeding activity, the cattle covers the caldera throughout the day;this unevens the topography and destroys the meadow. Hazards of volcanological origin are not yet occurring in LC;but the recent Lake Monoun (1984) and Nyos (1986) CO2 eruptions, mount Cameroon eruptions (1999 and 2000) and mount Oku Lake event (2011) which are close to the BV and, the age of 0 Myr of basalt, constitutes a subject of controversy toward the reactivation of the Cameroonian hotspot faults. The assessment of risks in LC was based on the average income of breeding activity and house investment. The economy of LC is valued at about US$527472.527. The level of such risk will be important in case of loss of human beings and the destruction of geomorphosites’ values. In order to reduce the level of looses in this zone, hazard and risks maps are provided in this paper as well as some recommendations.
文摘<p align="justify"> <span style="font-family:Verdana;"></span><span style="font-family:Verdana;"></span>Soil organic carbon (SOC) mineralization was carried out on soil samples collected from two depths: 0 - 20 cm and 20 - 40 cm for all land use (LU) types (grasslands, croplands, natural forest/fallow lands, cocoa/palm plantations, and settlement/agro-forests). Microbiological analyses were carried out by measuring microbial activity in 40 g of dried soil samples wetted to 60% water holding capacity and incubated at 27 °C. Carbon dioxide (CO<sub>2</sub>) emission was measured for 10 weeks using a CO<sub>2</sub> trap. Descriptive and graphical analyses of CO<sub>2</sub> respiration were done using CO<sub>2 </sub>emission data. Models were developed to describe CO<sub>2</sub> respiration and the first order kinetic model provided best fit to C-mineralization. Potentially mineralizable carbon (C<sub>o</sub>) and C-mineralization rate were higher in grasslands than other LU types, indicating a higher rate of microbial activity and carbon cycling. Metabolic quotient was higher in forest/fallow lands and reflects greater stress of the microbial community and a high requirement of maintenance energy. Grasslands enhanced more SOC accumulation and decomposition, suggesting a better carbon sink than other land use and management systems (LUMS). Microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) varied across LU patterns with maximum values in grasslands and minimum values in natural forest/fallow lands insinuating better soil quality for grasslands. MBC and SOC positively correlated with C<sub>o</sub> and C-mineralization, which intimates that C-mineralization is influenced by availability of MBC and SOC. Metabolic quotient (qCO<sub>2</sub>) negatively correlated with microbial quotient (MBC:SOC), depicting that higher values of qCO<sub>2</sub> signify difficulties in using organic substrates during microbial activity as a result of low MBC:SOC. Changes in LUMS affected the mineralization kinetics of SOC in the study area. </p>
文摘The study on empowerment strategies for tourism sustainability was carried out in 16 geosites located in seven regencies. These include Karo, Dairi, Simalungun, Samosir, Toba Samosir, North Tapanuli, and Humbang Hasundutan, in Toba Caldera Region (TCA), North Sumatra Province. The empowerment strategies will enhance local and national tourism development policy directives, boost development geared towards community tourism interests, and achieve GGN directives according to the concepts outlined by UNESCO. This geotourism development has been formulated through a synthesis of various investigations including the analyses of government references, potential tourist attractions, and SWOT. Furthermore, the SWOT analysis showed that a travel plan combining the elements of cultural heritage and geosites is an alternative empowerment for sustainable regional development through geotourism, using Pusuk Bukit as a pilot area. Geosites have been mapped as the basis for Toba Caldera’s development.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.92162214,41773015,and U1812402)the Key Research and Development Program of Yunnan Province(202103AQ100003).
文摘Clay-type Li deposits are poised to play a pivotal role in addressing the surging global demand for Li.The McDermitt clay-type Li deposit,located in Nevada,is the largest Li deposit in the United States,with Li hosted by a clay-rich sequence of smectite-dominated intervals and illite-dominated intervals,respectively.However,the occurrence of Li and the genesis of Li-bearing minerals within smectite-dominated intervals have not been thoroughly investigated in previous research.Here,we studied the mineralogy,the in-situ Li distribution,and the bonding environments of Li within the smectite intervals using a combination of instru-mental techniques including scanning electron microscope,transmission electron microscope,time-of-flight secondary ion mass spectrometry,and nuclear magnetic resonance.Our results indicate that the smectite exhibits low crystallinity characteristics of lacustrine clay authigenesis and is com-monly found tofill the interstices among volcanic minerals or envelop them;Li is mainly hosted by Mg-smectite rather than the volcanic minerals.Within the tuffaceous sediment samples,the volcanic glass has undergone a transformation,resulting in its complete disappearance and alteration into clay minerals.Owing to the octahedral sites of Mg-smectite bounded in Li,it is referred to be hectorite.We interpret that the hectorite’s precipitation occurs in a high saline-alkaline water environment,a result of McDermitt tuffdissolution.This conclusion can be supported by the coexistence of spherulitic calcite and hectorite.Overall,this study confirms hectorite as the main Li-bearing mineral and increases the understanding of the genetic model of hectorite formation in intracontinental caldera basins.
