We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and...We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached-at 58km-the Earth’s mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth’s atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasicontinuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient(wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous(~1000x) volumetric change due to the supercritical nature of volatiles associated with the hot,volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ~12 h, the eruptive volume and mass are estimated at 1.9 km^(3) and~2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma-seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.展开更多
It is known that the Amazon region plays an important role in the global energy, hydrological cycle and carbon balance. This region has been suffering from the course of the past 40 years intense land use and land cov...It is known that the Amazon region plays an important role in the global energy, hydrological cycle and carbon balance. This region has been suffering from the course of the past 40 years intense land use and land cover changes. With this in mind, this study has examined possible associations between change in spatial and temporal rainfall variability and land cover change in the Amazon, using the PRECIS regional modelling system. It has been found that the impacts of land cover change by forest removal are more intense in the so-called “Arc of deforestation” over central and southern Amazonia. However, the relative impact of the simulated rainfall changes seems to be more important in the JJA dry season. In addition, the simulations under the deforestation scenarios also show the occurrence of extreme rainfall events as well as more frequent dry periods. Therefore, the results found show to be potentially important in the modulation of regional climate variations which have several environmental and socio-economic impacts.展开更多
Fine-grained disseminated carbonate was found in Holocene sediments in a core taken from the northern basin of Lake Baikal. The core had two distinct facies. a terrigenous blue-clay overlain by a diatomaceous silt. Ox...Fine-grained disseminated carbonate was found in Holocene sediments in a core taken from the northern basin of Lake Baikal. The core had two distinct facies. a terrigenous blue-clay overlain by a diatomaceous silt. Oxygen and carbon stable isotope analyses, combined with SEM , X-ray diffraction and .palynology, show that the carbonate in the blue-clay layer is pedogenic in origin, rather than biogenic or authigenic . The S C values in the blue clay suggest that the carbonate is derived from a single source , while the carbonate in the diatom-rich layer might be transported by winds from different sources. On the assumption that the carbonate was formed during the post-glacial age and was transported primarily by river runoff, the 18O isotopic values suggest that the annual temperature in the northern Baikal drainage area was about 3℃ warmer during the middle Holocene (8500-7000 a, B. P.) than during the early Holocene (11 000-8 500a, B.P.) when the blue clay was being deposited . This interpretation展开更多
Accessory minerals with so-called granular texture have risen in importance as geochronological tools for U-Pb dating of meteorite impact events. Grain-scale recrystallization, typically triggered by a combination of ...Accessory minerals with so-called granular texture have risen in importance as geochronological tools for U-Pb dating of meteorite impact events. Grain-scale recrystallization, typically triggered by a combination of high-strain deformation and post-impact heating, can create a polycrystalline microstructure consisting of neoblasts that expel radiogenic Pb, which are thus ideal for isotopic dating. While granular domains in zircon and monazite from shocked rocks have been demonstrated to preserve impact ages,few U-Pb dating studies have been conducted on granular microstructures in titanite(CaTiSiO;). Here we report the occurrence of granular-textured titanite from ~2020 Ma granite basement rock exposed in the rim of the 4–5 Ma Roter Kamm impact structure in Namibia. Orientation mapping reveals two microstructurally distinct titanite populations: one consisting of strained/deformed grains, and the other consisting of grains that comprise aggregates of strain-free neoblasts. In situ U-Pb geochronology on 37 grains shows that most grains from both titanite populations yield indistinguishable U-Pb dates of ca.1025 Ma, consistent with the observed microstructures forming during the Mesoproterozoic Namaqua Orogeny. Only four grains preserved older age domains, recording ca. 1875 Ma Paleoproterozoic metamorphism. Two significant observations emerge:(1) none of the analyzed titanite grains yield the 2020 Ma igneous crystallization age previously established from zircon in the same sample, and(2) no age-resetting was detected that could be attributed to the 4 to 5 Ma Roter Kamm impact event.Despite the similarity of the neoblastic microstructure to minerals from other sites with an established impact provenance, the granular texture and near-complete Pb-loss in titanite from Roter Kamm granite instead records a Paleo-to Mesoproterozoic polymetamorphic history, rather than Miocene age shockrelated processes. These results highlight the critical importance of grain-scale context for interpretation of U-Pb data in granular titanite, and the potential for misinterpreting inherited(pre-impact) microstructures as impact-related phenomenon in target rocks with a complex geological history.展开更多
The ~1.8 billion years old North China Craton(NCC)has been thermally rejuvenated during the Mesozoic,experiencing two major phases of crustal extension and volcanism since then.The earlier phase of extension,lasted fr...The ~1.8 billion years old North China Craton(NCC)has been thermally rejuvenated during the Mesozoic,experiencing two major phases of crustal extension and volcanism since then.The earlier phase of extension,lasted from middle Mesozoic to early Cenozoic,was widespread in eastern NCC and accompanied with extensive volcanism.The later phase of extension,started in late Cenozoic and is active today,has been localized around the Ordos block,a residual core of the NCC,with limited volcanism.Here we investigate the causes of the NCC extension using finite element method.Numerical results indicate that the diffuse and closely-spaced extension during Mesozoic and early Cenozoic requires a thin and weak lithosphere,which supports the notion of significant lithospheric thinning under the eastern NCC,perhaps by delamination or thermal erosion of the lithospheric root.The western NCC,including the Ordos block,was largely spared by this phase of extension.The late Cenozoic extension around the Ordos block is commonly attributed to the Indo-Asian collision and mantle flow under eastern NCC.Our numerical results show that,regardless of the causing mechanism,a relatively thick and strong lithosphere is needed for the localized extension in western NCC,and preexisting weak zones in the lithosphere is a necessary condition for localized rifting around the Ordos.This preexisting lithospheric weakness is most likely inherited from the amalgamation of the NCC basement ~1.8 billion years ago.The late Cenozoic circum-Ordos rifting thus illustrates the control of ancient continental structures on recent tectonics.展开更多
基金partially supported by US Department of Energy Grant DE-SC0019759National Science Foundation (NSF) Grants EAR-1918126, EAR-2027150, EAR-1925965, and OCE-1842989。
文摘We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached-at 58km-the Earth’s mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth’s atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasicontinuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient(wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous(~1000x) volumetric change due to the supercritical nature of volatiles associated with the hot,volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ~12 h, the eruptive volume and mass are estimated at 1.9 km^(3) and~2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma-seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.
文摘It is known that the Amazon region plays an important role in the global energy, hydrological cycle and carbon balance. This region has been suffering from the course of the past 40 years intense land use and land cover changes. With this in mind, this study has examined possible associations between change in spatial and temporal rainfall variability and land cover change in the Amazon, using the PRECIS regional modelling system. It has been found that the impacts of land cover change by forest removal are more intense in the so-called “Arc of deforestation” over central and southern Amazonia. However, the relative impact of the simulated rainfall changes seems to be more important in the JJA dry season. In addition, the simulations under the deforestation scenarios also show the occurrence of extreme rainfall events as well as more frequent dry periods. Therefore, the results found show to be potentially important in the modulation of regional climate variations which have several environmental and socio-economic impacts.
文摘Fine-grained disseminated carbonate was found in Holocene sediments in a core taken from the northern basin of Lake Baikal. The core had two distinct facies. a terrigenous blue-clay overlain by a diatomaceous silt. Oxygen and carbon stable isotope analyses, combined with SEM , X-ray diffraction and .palynology, show that the carbonate in the blue-clay layer is pedogenic in origin, rather than biogenic or authigenic . The S C values in the blue clay suggest that the carbonate is derived from a single source , while the carbonate in the diatom-rich layer might be transported by winds from different sources. On the assumption that the carbonate was formed during the post-glacial age and was transported primarily by river runoff, the 18O isotopic values suggest that the annual temperature in the northern Baikal drainage area was about 3℃ warmer during the middle Holocene (8500-7000 a, B. P.) than during the early Holocene (11 000-8 500a, B.P.) when the blue clay was being deposited . This interpretation
基金Support was provided by the Space Science and Technology Centre at Curtin University, a Curtin Research Fellowship
文摘Accessory minerals with so-called granular texture have risen in importance as geochronological tools for U-Pb dating of meteorite impact events. Grain-scale recrystallization, typically triggered by a combination of high-strain deformation and post-impact heating, can create a polycrystalline microstructure consisting of neoblasts that expel radiogenic Pb, which are thus ideal for isotopic dating. While granular domains in zircon and monazite from shocked rocks have been demonstrated to preserve impact ages,few U-Pb dating studies have been conducted on granular microstructures in titanite(CaTiSiO;). Here we report the occurrence of granular-textured titanite from ~2020 Ma granite basement rock exposed in the rim of the 4–5 Ma Roter Kamm impact structure in Namibia. Orientation mapping reveals two microstructurally distinct titanite populations: one consisting of strained/deformed grains, and the other consisting of grains that comprise aggregates of strain-free neoblasts. In situ U-Pb geochronology on 37 grains shows that most grains from both titanite populations yield indistinguishable U-Pb dates of ca.1025 Ma, consistent with the observed microstructures forming during the Mesoproterozoic Namaqua Orogeny. Only four grains preserved older age domains, recording ca. 1875 Ma Paleoproterozoic metamorphism. Two significant observations emerge:(1) none of the analyzed titanite grains yield the 2020 Ma igneous crystallization age previously established from zircon in the same sample, and(2) no age-resetting was detected that could be attributed to the 4 to 5 Ma Roter Kamm impact event.Despite the similarity of the neoblastic microstructure to minerals from other sites with an established impact provenance, the granular texture and near-complete Pb-loss in titanite from Roter Kamm granite instead records a Paleo-to Mesoproterozoic polymetamorphic history, rather than Miocene age shockrelated processes. These results highlight the critical importance of grain-scale context for interpretation of U-Pb data in granular titanite, and the potential for misinterpreting inherited(pre-impact) microstructures as impact-related phenomenon in target rocks with a complex geological history.
基金support from NSF (grants EAR-1519980 and OISE-0730154)NSFC (grant 41374104)
文摘The ~1.8 billion years old North China Craton(NCC)has been thermally rejuvenated during the Mesozoic,experiencing two major phases of crustal extension and volcanism since then.The earlier phase of extension,lasted from middle Mesozoic to early Cenozoic,was widespread in eastern NCC and accompanied with extensive volcanism.The later phase of extension,started in late Cenozoic and is active today,has been localized around the Ordos block,a residual core of the NCC,with limited volcanism.Here we investigate the causes of the NCC extension using finite element method.Numerical results indicate that the diffuse and closely-spaced extension during Mesozoic and early Cenozoic requires a thin and weak lithosphere,which supports the notion of significant lithospheric thinning under the eastern NCC,perhaps by delamination or thermal erosion of the lithospheric root.The western NCC,including the Ordos block,was largely spared by this phase of extension.The late Cenozoic extension around the Ordos block is commonly attributed to the Indo-Asian collision and mantle flow under eastern NCC.Our numerical results show that,regardless of the causing mechanism,a relatively thick and strong lithosphere is needed for the localized extension in western NCC,and preexisting weak zones in the lithosphere is a necessary condition for localized rifting around the Ordos.This preexisting lithospheric weakness is most likely inherited from the amalgamation of the NCC basement ~1.8 billion years ago.The late Cenozoic circum-Ordos rifting thus illustrates the control of ancient continental structures on recent tectonics.
