The paradigm of an ancient warm, wet, and dynamically active Mars, which transitioned into a cold, dry, and internally dead planet, has persisted up until recently despite published Viking-based geologic maps that indicate geologic and hydrologic activity extending into the Late Amazonian epoch. This paradigm is shifting to a water-enriched planet, which may still exhibit internal activity, based on a collection of geologic, hydrologic, topographic, chemical, and elemental evidences obtained by the Viking, Mars Global Surveyor (MGS), Mars Odyssey (MO), Mars Exploration Rovers (MER), and Mars Express (MEx) missions. The evidence includes: (1) stratigraphically young rock materials such as pristine lava flows with few, if any, superposed impact craters; (2) tectonic features that cut stratigraphically young materials; (3) features with possible aqueous origin such as structurally controlled channels that dissect stratigraphically young materials and anastomosing-patterned slope streaks on hillslopes; (4) spatially varying elemental abundances for such elements as hydrogen (H) and chlorine (Cl) recorded in rock materials up to 0.33 m depth; and (5) regions of elevated atmospheric methane. This evidence is pronounced in parts of Tharsis, Elysium, and the region that straddles the two volcanic provinces, collectively referred to here as the Tharsis/Elysium corridor. Based in part on field investigations of Solfatara Crater, Italy, recommended as a suitable terrestrial analog, the Tharsis/Elysium corridor should be considered a prime target for Mars Reconnaissance Orbiter (MRO) investigations and future science-driven exploration to investigate whether Mars is internally and hydrologically active at the present time, and whether the persistence of this activity has resulted in biologic activity. 相似文献
The aim of this study was to provide a contribution to seismic hazard assessment of the Salento Peninsula (Apulia, southern Italy). It is well known that this area was struck by the February 20, 1743, earthquake (I0 = IX and Mw = 7.1), the strongest seismic event of Salento, that caused the most severe damage in the towns of Nardò (Lecce) and Francavilla Fontana (Brindisi), in the Ionian Islands (Greece) and in the western coast of Albania. It was also widely felt in the western coast of Greece, in Malta Islands, in southern Italy and in some localities of central and northern Italy. Moreover, the area of the Salento Peninsula has also been hit by several low-energy and a few high-energy earthquakes over the last centuries; the instrumental recent seismicity is mainly concentrated in the western sector of the peninsula and in the Otranto Channel. The Salento area has also experienced destructive seismicity of neighboring regions in Italy (the Gargano Promontory in northern Apulia, the Southern Apennines chain, the Calabrian Arc) and in the Balkan Peninsula (Greece and Albania). Accordingly, a critical analysis of several documentary and historical sources, as well as of the geologic–geomorphologic ground effects due to the strong 1743 Salento earthquake, has been carried out by the authors in this paper; the final purpose has been to re-evaluate the 1743 MCS macroseismic intensities and to provide a list of newly classified localities according to the ESI-07 scale on the base of recognized Earthquake Environmental Effects. The result is a quite different damage scenario due to this earthquake that could raise the seismic potential currently recognized for the Salento area, and consequently upgrade the seismic hazard classification of the Salento. Indeed it is important to remind that currently, despite the intense earthquake activity recorded not only in the Otranto Channel, but especially in Greece and Albania, this area is classified in the least dangerous category of the Seismic Classification of the Italian territory (IV category). 相似文献
In the convergence slope/coastal areas of Antarctica, a large fraction of snow is continuously eroded and exported by wind to the atmosphere and into the ocean. Snow transport observations from instruments and satellite images were acquired at the wind convergence zone of Terra Nova Bay (East Antarctica) throughout 2006 and 2007. Snow transport features are well-distinguished in satellite images and can extend vertically up to 200 m as first-order quantitatively estimated by driftometer sensor FlowCapt?. Maximum snow transportation occurs in the fall and winter seasons. Snow transportation (drift/blowing) was recorded for ~80% of the time, and 20% of time recorded, the flux is >10?2 kg m?2 s?1 with particle density increasing with height. Cumulative snow transportation is ~4 orders of magnitude higher than snow precipitation at the site. An increase in wind speed and transportation (~30%) was observed in 2007, which is in agreement with a reduction in observed snow accumulation. Extensive presence of ablation surface (blue ice and wind crust) upwind and downwind of the measurement site suggest that the combine processes of blowing snow sublimation and snow transport remove up to 50% of the precipitation in the coastal and slope convergence area. These phenomena represent a major negative effect on the snow accumulation, and they are not sufficiently taken into account in studies of surface mass balance. The observed wind-driven ablation explains the inconsistency between atmospheric model precipitation and measured snow accumulation value. 相似文献
The complexity of the processes responsible for volcanic eruptions makes a theoretical approach to forecasting the evolution of volcanic unrest rather difficult. A feasible strategy for this purpose appears to be the identification of possible repetitive schemes (patterns) in the pre-eruptive unrest of volcanoes. Nevertheless, the limited availability and the heterogeneity of pre-eruptive data, and the objective difficulty in quantitatively recognizing complex pre-eruptive patterns, make this task very difficult. In this work we address this issue by using a pattern recognition approach applied to the seismicity recorded during 217 volcanic episodes of unrest around the world. In particular, we use two non-parametric algorithms that have proven to give satisfactory results in dealing with a small amount of data, even if not normally distributed and/or characterized by discrete or categorical values. The results show evidence of a longer period of instability in the unrest preceding an eruption, compared to isolated unrest. This might indicate, even if not necessarily, a difference in the energy of processes responsible for the two types of unrest. However, if the unrest is followed by an eruption, it seems that the seismic energy released during the unrest (parameterized by the duration of the swarm and the maximum magnitude recorded) is not indicative of the magnitude of the impending eruption. We also found that, in general, unrest followed by the largest explosive eruptions have a longer repose time than those related to moderate eruptions. This evidence supports the fact that the occurrence of a large eruption needs a sufficient amount of time after the last event in order to re-charge the feeding system and to achieve a closed-conduit regime so that a sufficiently large amount of gas can be accumulated.Editorial responsibility: T. Druitt 相似文献
Volcanic activity can enhance several secondary effects, including the formation of one or more natural dams. A common example
is from volcanic collapse, where huge mass volumes are rapidly emplaced, obstructing the drainage around a volcano. Their
duration depends on the volume of the obstructing mass, inflow rate, and on its textural characteristics. A block facies of
a debris avalanche produces durable and permeable dams that consist of decimeter to meter-sized blocks without matrix, whereas
a mixed facies is easily eroded after overflowing. Analysis of the sedimentological characteristics of different volcaniclastic
deposits that formed natural dams indicate that a mean grain size (Md) equal to −1 phi divides the field of debris avalanche
dams (Md < −1 phi) from that formed from other types of volcanic deposits. In addition, the matrix proportion of dams formed
by debris avalanches are less than the 50% and the percentage of mud fraction is highly variable, up to 30%. Combining the
granulometric textures with duration time of the dam shows no clear relation. Dam durability is probably more dependent on
the volume of the lake and the inflow rate. Only in some cases, as mud fraction increases is the blockage also less durable
because the lower permeability favors rapid infilling. The texture of the dam also determines the types of secondary flows
that originate by their breakdown. These vary from cohesive debris flow to hyperconcentrated flow, representing different
hazards due to their magnitude and their different behavior downstream. 相似文献
After the major 1991–1993 eruption, Mt. Etna resumed flank activity in July 2001 through a complex system of eruptive fissures
cutting the NE and the S flanks of the volcano and feeding effusive activity, fire fountains, Strombolian and minor phreatomagmatic
explosions. Throughout the eruption, magmas with different petrography and composition were erupted. The vents higher than
2,600 m a.s.l. (hereafter Upper vents, UV) erupted porphyritic, plagioclase-rich trachybasalt, typical of present-day summit
and flank activity. Differently, the vents located at 2,550 and 2,100 m a.s.l. (hereafter Lower vents, LV) produced slightly
more primitive trachybasalt dominated by large clinopyroxene, olivine and uncommon minerals for Etna such as amphibole, apatite
and orthopyroxene and containing siliceous and cognate xenoliths. Petrologic investigations carried out on samples collected
throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity, namely the coeval
occurrence of distinct magmas. We interpret this evidence as the result of a complex plumbing system. It consists in two separate
magma storage systems: a shallow one feeding the activity of the UV and a deeper and more complex storage related to the activity
of LV. In this deep storage zone, which is thermally and compositionally zoned, the favourable conditions allow the crystallization
of amphibole and the occurrence of cognate xenoliths representing wall cumulates. Throughout 2001 eruption, UV and LV magmas
remain clearly distinct and ascended following different paths, ruling out the occurrence of mixing processes between them.
Furthermore, integrating the 2001 eruption in the framework of summit activity occurring since 1995, we propose that the 2001
magma feeding the vents lower than 2,600 m a.s.l. is a precursor of a refilling event, which reached its peak during the 2002–2003
Etna flank eruption. 相似文献
The temporal evolution of the Yemen Trap series is examined in the light of K-Ar radiometric data.Rifting and volcanic activity characterize the Yemen plateau between 30 and 20 m.y. confirming a fairly common history of the Afro-Arabian plate on both sides of the Red Sea. 相似文献
During the summer of 1992 a geological expedition crossed the northern Karakorum range in northern Pakistan, from the Chitral
to Karambar valleys, from the villages of Mastuj to Imit. Some of the areas visited were geologically unknown. A number of
structural units were crossed, belonging to the Karakorum block or to other crustal blocks north of it. They are: (a) the
axial batholith, in which three plutonic bodies have been identified, and (b) the northern sedimentary belt (NSB), in which
three major tectonostratigraphic units form thrust stacks dipping to the north. Their internal stratigraphy and structural
style are partly different. The most complete contains a crystalline basement, transgressed by a marine succession during
the Early Ordovician. The youngest strata are represented by the Reshun conglomerate, of inferred Cretaceous age. The northernmost
unit of the NSB is tightly folded, whereas the central one forms a monocline. Vertical faults, mainly strike-slip, dissect
the thrusted slabs. Metamorphic deformation is absent or reaches only the anchizone in the studied sector of the Karakorum
NSB. To the north of the Karakorum proper there are several other tectonic units, separated by vertical faults. They are,
from south to north: (a) the Taš Kupruk zone, with metavolcanics of basaltic to latibasaltic composition; (b) the Atark unit,
mostly consisting of massive carbonate rocks of Mesozoic age; and (c) the Wakhan slates which consist of a thick widespread
succession of dark slates, metasiltites and sandstones. The fine-grained elastic rocks are supposed to be Palaeozoic to Early
Triassic in age. The Wakhan slates are intruded by plutons belonging to the East Hindu Kush batholith, from which a single
K/Ar age on muscovite gave a Jurassic age. 相似文献
The aim of this study was to provide a contribution to seismic hazard assessment of the Salento Peninsula (Apulia, southern Italy). It is well known that this area was struck by the February 20, 1743, earthquake (I0 = IX and Mw = 7.1), the strongest seismic event of Salento, that caused the most severe damage in the towns of Nardò (Lecce) and Francavilla Fontana (Brindisi), in the Ionian Islands (Greece) and in the western coast of Albania. It was also widely felt in the western coast of Greece, in Malta Islands, in southern Italy and in some localities of central and northern Italy. Moreover, the area of the Salento Peninsula has also been hit by several low-energy and a few high-energy earthquakes over the last centuries; the instrumental recent seismicity is mainly concentrated in the western sector of the peninsula and in the Otranto Channel. The Salento area has also experienced destructive seismicity of neighboring regions in Italy (the Gargano Promontory in northern Apulia, the Southern Apennines chain, the Calabrian Arc) and in the Balkan Peninsula (Greece and Albania). Accordingly, a critical analysis of several documentary and historical sources, as well as of the geologic–geomorphologic ground effects due to the strong 1743 Salento earthquake, has been carried out by the authors in this paper; the final purpose has been to re-evaluate the 1743 MCS macroseismic intensities and to provide a list of newly classified localities according to the ESI-07 scale on the base of recognized Earthquake Environmental Effects. The result is a quite different damage scenario due to this earthquake that could raise the seismic potential currently recognized for the Salento area, and consequently upgrade the seismic hazard classification of the Salento. Indeed it is important to remind that currently, despite the intense earthquake activity recorded not only in the Otranto Channel, but especially in Greece and Albania, this area is classified in the least dangerous category of the Seismic Classification of the Italian territory (IV category).