Volcanic hazards in the surroundings of Pico de Orizaba,eastern Mexico

Volcanic hazards from Pico de Orizaba volcano are presented here tor the first time. Some 1.3 million people live within the hazard zone, which in the most severe case would encompass the Mexican Gulf coast, east of the volcano. Three major cities located in the eastern part of the hazard zone account for 800 000 of this population and about 200 000 people live within a 20 km radius of the volcano. Probability calculations are presented as an attempt to quantify the hazards in the surroundings of the volcano. Such quantification can be of use in planning for future land use within the hazard zones.A zone of about 10 km radius centred on the top crater is a high hazard zone for gravity-driven flows and fallout ejecta. For large volume eruptions, the radius could be extended to 120 km to the east and 60 km to the west. The asymmetrical distribution is related to the topography of the volcano. Hazards from Pyroclastic-fall deposits are principally to the west of the volcano, since easterly winds are dominant in the area lava-flow hazards are greatest within a 10 km radius from the summit crater. Pyroclastic flow hazards are high up to 20 km from the volcano summit.In the case of reactivation of the volcano, melting of a glacier covering the summit of Pico de Orizaba having a volume equivalent to some 45 × 10⁹ litres of water, would produce lahars which would descend the flanks of the volcano.     

Volcanic hazards zonation of the Nevado de Toluca Volcano,Central Mexico

Nevado de Toluca Volcano (NTV), located in central Mexico, is a large stratovolcano, with an explosive history. The area is one of the most important developing centers (>2 millions) in Mexico and in the last 30 yrs large population growth and expansion have increased the potential risk in case of a reactivation of the volcano. As part of a study to assess volcanic risk, this paper presents the results of the volcanic hazard analysis for the NTV. A total of 150 stratigraphic sections were made in the field and three new ages were obtained. Eruptions from NTV produced a complex sequence of pyroclastic deposits that have affected the area at least 18 times during the last 100,000 yrs. Eight vulcanian, four plinian and one-ultraplinian eruptions as well as the destruction of at least three domes occurred in the last 42,000 yr BP as well as two sector collapses in the last 100,000 yrs. Isopach and isopleth maps for the main ulraplinian eruption were also made. The original cone height (5,080 m.a.s.l) was reconstructed through geomorphologic methods. The maximum distance calculated with the energy line for the block and ash flows was 41 km, 35 km for pumice flows and 45 km for debris avalanches. The dominant wind direction at altitudes of 20–30 km is to the east-northeast from November to March, west-northwest in April and west from May to October. Five hazards maps (block and ash flows, pumice flows, ash fall, debris avalanches, and lahars) were made for the NTV. The pyroclastic flows and lahars represent very high to medium hazard for Toluca, Villa Guerrero, Coatepec, Tianguistengo, Metepec, Tenango, Lerma and Zinacantepec. A new debris avalanche would probably affect the south and northeast because of active faulting (E–W and NW–SE) and existing topographic differences in height.     

The Vulnerability of Canada to Volcanic Hazards

Western Canada lies in a zone of active tectonics and volcanism, but thedispersed population has witnessed few eruptions due to the remoteness of the volcanoes and their low level ofactivity. This has created a false perception that Canada's volcanoes are extinct.There are more than 200 potentially-active volcanoes in Canada, 49of which have erupted in the past 10,000 years. They occur in five belts, with origins related totectonic environment. The minimum annual probability of a Canadian volcanic eruption is approximately 1/200;for an effusive (lava) eruption the probability is about 1/220, and for a significant explosive eruptionit is about 1/3333. In-progress studies show that there have been earthquakes associated with at least 9 ofthe youngest Canadian volcanoes since 1975. A scenario of an eruption of Mt. Cayley (50.1°N,123.3°W) shows how western Canada is vulnerable to an eruption. The scenario is basedon past activity in the Garibaldi volcanic belt and involves both explosive and effusive activity.The scenario impact is largely a result of the concentration of vulnerable infrastructure in valleys.Canadian volcanoes are monitored only by a regional seismic network,that is capable of detecting a M > 2 event in all potentially-active areas.This level of monitoring is probably sufficient to alert scientistsat or near eruption onset, but probably insufficient to allow a timelyforecast of activity. Similarly the level of geological knowledge about the volcanoes is insufficient to createhazard maps. This will improve slightly in 2002 when additional monitoring is implemented in theGaribaldi volcanic belt. The eruption probabilities, possible impacts, monitoring limitations and knowledgegaps suggest that there is a need to increment the volcanic risk mitigation efforts.     

Volcanic and anthropogenic contributions to global weathering budgets

We evaluate whether the global weathering budget is near steady state for the pre-anthropogenic modern environment by assessing the magnitude of acidity-generating volcanic exhalations. The weathering rate induced by volcanic acid fluxes, of which the CO₂ flux is the most important, can be expressed as an average release rate of dissolved silica, based on a model feldspar-weathering scheme, and the ratio of carbonate-to-silicate rock weathering. The theoretically predicted flux of silica from chemical weathering is slightly smaller than the estimated global riverine silica flux. After adjustment for carbonate weathering, the riverine dissolved bicarbonate flux is larger than the volcanic carbon degassing rate by a factor of about three. There are substantial uncertainties associated with the calculated and observed flux values, but the modern system may either not be in steady state, or additional, “unknown” carbon sources may exist. The closure errors in the predicted budgets and observed riverine fluxes suggest that continental weathering rates might have had an impact on atmospheric CO₂ levels at a time scale of 10³-10⁴ years, and that enhanced weathering rates during glacial periods might have been a factor in the reduced glacial atmospheric CO₂ levels. Recent anthropogenic emissions of carbon and sulfur have a much larger acid-generating capacity than the natural fluxes. Estimated potential weathering budgets to neutralize these fluxes are far in excess of observed values. A theoretical scenario for a return to steady state at the current anthropogenic acidity emissions (disregarding the temporary buffering action of the ocean reservoir) requires either significantly lower pH values in continental surface waters as a result of storage of strong acids, and/or higher temperatures as a result of enhanced atmospheric CO₂ levels in order to create weathering rates that can neutralize the total flux of anthropogenic and natural background acidity.     

The Cold Bay Volcanic Center,Aleutian Volcanic arc

The widespread abundance of Hi-Alumina Basalt (HAB) lavas in most volcanic arcs has been suggested by some as evidence for a primary, parental HAB magma generated by the high pressure melting of subducted oceanic crust (quartz eclogite). Others suggest a parental, mantle-derived olivine tholeiite magma which produces HAB magmas through fractionation of olivine, clinopyroxene, chrome-spinel +/– plagioclase. The petrology and geochemistry of seven HAB lavas from the Aleutian Cold Bay Volcanic Center have been studied in order to specifically address these two possibilities. All lavas show mineralogical and compositional features typical of most Aleutian HAB lavas. Coexisting opx and cpx in a closely associated basaltic-andesite indicate a minimum pre-eruption temperature of 1,110° C. A comparison of the observed (plag-tmag-olivcpx) and experimentally determined crystallization sequences yields a minimum pre-eruption pressure estimate of 7 kb and estimated H₂O contents of 0.7 wt.%. Maximum pre-eruption f _{o 2} values have been estimated at NNO+0.6 log units.Mass balance calculations demonstrate that the HAB compositions are satisfied by the fractionation of olivine, clinopyroxene +/– plagioclase from a primitive (Mg-# > 65) parental tholeiite. Plagioclase accumulation does not play a significant role in their origin. Many of the same compositional characteristics are also satisfied by high pressure melting of altered ocean ridge tholeiite +5 v.% pelagic sediment (quartz eclogite). The available HAB phase equilibria data do not support a fractionation origin but do support an origin involving high pressure melting of quartz eclogite. The lack of compositional zonation in the HAB phenocrysts, and the complete absence of disequilibrium MgO-rich mafic phenocrysts further argue against a tholeiite fractionation origin.Consideration of all these features indicates that the geochemical data are permissive in their interpretation. A process involving tholeiite fractionation successfully predicts the compositions of the HAB lavas but is at odds with the mineralogical and phase equilibria evidence. With some exceptions (notably Ni, Cr and Sr abundances), a process of high pressure quartz eclogite melting is consistent with the compositional, mineralogical and phase equilibria characteristics of these HAB lavas. When the relative merits of both origins are weighed it is apparent that a quartz eclogite source satisfies more of important features of these HAB lavas.Extrusive rocks have been grouped on a basis of SiO₂ content into basalt (<52 wt.%), basaltic-andesite (52–56 wt.%) and andesite (>56 wt.%) after Ewart (1982)     

The Cold Bay Volcanic Center,Aleutian Volcanic Arc

The Cold Bay Volcanic Center has experienced two major stages of eruptive activity. Early (M-Series) acitivity produced bimodal Hi-Alumina basalt and calc-alkaline andesite lavas while later (FPK-Series) activity produced only calc-alkaline andesite. The spectrum of basalt compositions is believed to be due to high pressure (8 kb) fractionation at or near the base of the crust. Abundant mineralogical and geochemical evidence support a lower pressure mixing origin for all andesites. Inspection of the mineralogical data has shown that the earliest (M-Series) andesites were produced by mixing of basalt (<53 wt% SiO₂) and silicic andesite (60.5 to 62.5 wt%) while later (FPK-Series) andesites resulted from the mixing of basaltic-andesite (53 to 56 wt%) and less silicic andesite (58.5 to 60.0 wt%). The major element and trace element geochemical data are consistent with a low pressure fractionation origin for the silicic endmember magmas and support the temporal variations in both mafic and silicic endmember compositions. The complete lack of crustal inclusions in all lavas is taken as evidence for a minimal crustal melting and/or assimilation role in the origin of the silicic endmembers. Many of the features of all andesites, including the important long term convergence of endmember magma compositions, are consistent with the process of liquid fractionation, accompanied by large scale magma mixing. A deduced upper limit of 62.5 wt% SiO₂ for the silicic endmember magmas suggests that liquid fractionation, in the absence of major crustal melting, cannot produce more silicic magmas. A possible explanation is the presence of a rheological barrier, based on the concept of critical crystallinity (Marsh 1981), which prohibits more silicic liquids from being extracted from a crystal-liquid suspension.     

Volcanic gaps due to oblique consumption of aseismic ridges

The present-day consumption of oceanic ridges and other buoyant rises and fragments at circum-Pacific subduction zones, and presumably elsewhere, are closely related to existing gaps in volcanism. Examples are the gaps associated with the Nazca, Juan Fernandez, Cocos, Marcus-Necker and Louisville ridges. The buoyancy of these ridges breaks the continuity of the subducted plate, which may lead to reduced water supply required for melting of magma, and therefore create temporary volcanic gaps. The oblique consumption of these ridges causes the gap to migrate with time. This mechanism may be useful in interpreting time-space patterns of past volcanic chains associated with subduction in terms of the consumption of the disruptive oceanic plateaus and ridges.     

Analysis of social vulnerability to hazards in China

To improve natural disaster management, it is important to recognize the variability of the vulnerable populations exposed to hazards and to develop location-based emergency plans accordingly. This paper presents a mathematical model to establish a model of social vulnerability index (SoVI), which includes 12 social variables, and the regional social vulnerability to natural hazards was formulated by them. Taking a city as statistical unit, the variability of vulnerability to natural hazards was explored among the 323 cities based on the SoVI. The results indicate that vulnerability is a location-based regional phenomenon, with the most vulnerable cities being located in the southwest of China and the eastern areas being generally less vulnerable. The results will be helpful for policy makers to formulate disaster management plans, which can be beneficial for people in more vulnerable areas who are responding to, coping with, and recovering from natural disasters.     

Modelling intra-dependencies to assess road network resilience to natural hazards

Natural Hazards - Estimating the resilience of a road network (one of the essential critical infrastructures in times of crisis) to natural hazards is crucial in achieving the goals of disaster...     

Identification of alluvial fans susceptible to debris-flow hazards

We describe and test a method for identifying alluvial fans likely to be affected by debris flows. It is based on identifying catchment parameters by geographical information system interrogation of a digital elevation model, using the Melton ratio as the discriminating parameter. The method was calibrated using data from debris-flow-generating catchments in Coromandel and the adjacent Kaimai Ranges, North Island, NZ, and tested against data from the rest of New Zealand. The procedure is remarkably (but not completely) reliable for identifying debris-flow-capable catchments, and thus fans, across the wide range of climates and lithologies in New Zealand mountains. A case study illustrates the potential of the method for avoiding future hazards and emphasises the need for a precautionary approach when field investigations do not detect evidence for past debris flows.     

Resilience to natural hazards: a geographic perspective

Resilience is increasingly used as an approach for understanding the dynamics of natural disaster systems. This article presents the origin of resilience and provides an overview of its development to date, which draws on the wide literature on ecological science, social science, social–environmental system and natural hazards. From a geographic perspective, the model of disaster resilience of “Loss–Response” of Location (DRLRL) was created and disaster resilience was defined from three dimensional mode, which focused on the spatial, temporal scale of resilience and attributes of hazard-affected bodies. A geographic approach was put forward to measure the disaster resilience, including two properties of inherent resilience and adaptive resilience and a case study was implemented in order to validate this approach. This perspective would offer greater potential in application of resilience concept, especially in the process of integrated risk management and disaster recovery.     

Cryospheric hazards

Glaciers are an important element of the Earth system. Glaciers provide numerous, though poorly appreciated, ecological and economic benefits. However, glacial processes can also be hazards. Local glacial hazards include catastrophic floods from lakes impounded by glaciers and their moraines, landslides and debris flows induced by glacier thinning and retreat and permafrost thaw, and enhanced seismicity and volcanism due to large‐scale deglaciation. Regionally, rivers can be affected by changes in sediment supply from glacier forefields. Perhaps the greatest hazard that glaciers pose on a global scale of coastal erosion and flooding caused by sea‐level rise. If Earth's climate continues to warm, as scientists forecast, the rate of sea‐level rise will increase and some low‐lying coastal areas will be flooded by the end of this century.     

Volcanic passive margins

Compared to non-volcanic ones, volcanic passive margins mark continental break-up over a hotter mantle, probably subject to small-scale convection. They present distinctive genetic and structural features. High-rate extension of the lithosphere is associated with catastrophic mantle melting responsible for the accretion of a thick igneous crust. Distinctive structural features of volcanic margins are syn-magmatic and continentward-dipping crustal faults accommodating the seaward flexure of the igneous crust. Volcanic margins present along-axis a magmatic and tectonic segmentation with wavelength similar to adjacent slow-spreading ridges. Their 3D organisation suggests a connection between loci of mantle melting at depths and zones of strain concentration within the lithosphere. Break-up would start and propagate from localized thermally-softened lithospheric zones. These ‘soft points’ could be localized over small-scale convection cells found at the bottom of the lithosphere, where adiabatic mantle melting would specifically occur. The particular structure of the brittle crust at volcanic passive margins could be interpreted by active and sudden oceanward flow of both the unstable hot mantle and the ductile part of the lithosphere during the break-up stage. To cite this article: L. Geoffroy, C. R. Geoscience 337 (2005).     

Mountain hazards

The review examines mountain land risks, especially those that involve sudden, more or less localized bouts of damage and disasters. Geographers' studies to date have mainly dealt with natural hazards, emphasizing those like avalanches, large landslides or natural dams that are uniquely associated with mountain environments. Such work is briefly reviewed. Earthquake risks are then singled out to help define and discuss problems faced by this work. They are shown to depend strongly upon aspects of mountain environments other than seismicity. Human vulnerability appears to be mainly dependent upon socioeconomic and habitat conditions which, although they determine seismic impacts, may and usually do develop independent of it. Moreover, these ingredients of risk are most closely associated with, or definitive of, the mountain people and areas. They are most strongly influenced by human agency, both in deciding who and what are exposed to risk, and in actually increasing or decreasing unfavorable responses to earthquakes. Recent earthquake disasters in the mountains also record how rapid changes in these social and habitat conditions, rather than seismicity, are increasing the scale and altering the forms of damage. These changes in turn, however, are largely dependent upon developments, initiatives and penetration from outside the mountains, and responses of mountain people more or less enforced by them. The importance of so-called highland-lowland interactions, is even more obvious in the most destructive of human hazards discussed, those of war and other armed violence. Mountain lands and peoples are shown to have been subject to recurrent warring, and a disproportionate share of the deployment of state violence in this century. Most of the casualties are resident civilians. They have been usually threatened by other uses of armed violence, including insurgency and counter-insurgency warfare and genocidal actions by state forces. Refugees and expellees from war zones have included great numbers of mountain folk. Another fast growing hazard of the late twentieth century, not unrelated to war and militarism, the international trafficking in and addiction plagues of hard drugs, has a unique relation to mountains. The South American growers of the coca leaf, and Southwest and Southeast Asian growers of the opium poppy are mountain farmers. Their participation is bringing a range of severe risks to their high valleys, as well as benefits. Finally the paper addresses the conceptual problems brought about by the compounding of determinist assumptions in both mountain land and hazards research. These include not only environmental determinist notions, or related Neo-Malthusian and Social Darwinist ideas, but the various historicist ones of assumed technological, economic and political stages of development. It is argued that such social constructions of the problem of hazards and disaster are dubious, and have become a major impediment to understanding and risk mitigation. Alternative frameworks require more attention to the regional, state, and global patterns of influence shaping risk in mountain lands, but also to the human ecology of mountain societies taking account of matters to which the expediences of technocratic expertise have made us blind.     

Erratum to: Review of post-collisional volcanism in the Central Anatolian Volcanic Province (Turkey), with special reference to the Tepekoy Volcanic Complex

Neogene-Quaternary post-collisional volcanism in Central Anatolian Volcanic Province (CAVP) is mainly characterized by calc-alkaline andesites-dacites, with subordinate tholeiitic-transitional-mildly alkaline basaltic volcanism of the monogenetic cones. Tepekoy Volcanic Complex (TVC) in Nigde area consists of base surge deposits, and medium to high-K andesitic-dacitic lava flows and basaltic andesitic flows associated with monogenetic cones. Tepekoy lava flows petrographically exhibit disequilibrium textures indicative of magma mixing/mingling and a geochemisty characterized by high LILE and low HFSE abundances, negative Nb–Ta, Ba, P and Ti anomalies in mantle-normalized patterns. In this respect, they are similar to the other calc-alkaline volcanics of the CAVP. However, TVC lava flows have higher and variable Ba/Ta, Ba/Nb, Nb/Zr, Ba/TiO₂ ratios, indicating a heterogeneous, variably fluid-rich source. All the geochemical features of the TVC are comparable to orogenic andesites elsewhere and point to a sub-continental lithospheric mantle source enriched in incompatible elements due to previous subduction processes. Basaltic monogenetic volcanoes of CAVP display similar patterns, and HFS anomalies on mantle-normalized diagrams, and have incompatible element ratios intermediate between orogenic andesites and within-plate basalts (e.g. OIB). Accordingly, the calc-alkaline and transitional-mildly alkaline basaltic magmas may have a common source region. Variable degrees of partial melting of a heterogeneous source, enriched in incompatible elements due to previous subduction processes followed by fractionation, crustal contamination, and magma mixing in shallow magma chambers produced the calc-alkaline volcanism in the CAVP. Magma generation in the TVC, and CAVP in general is via decompression melting facilitated by a transtensional tectonic regime. Acceleration of the extensional regime, and transcurrent fault systems extending deep into the lithosphere favoured asthenospheric upwelling at the base of the lithosphere, and as a consequence, an increase in temperature. This created fluid-present melting of a fluid-enriched upper lithospheric mantle or lower crustal source, but also mixing with asthenosphere-derived melts. These magmas with hybrid source characteristics produced the tholeiitic-transitional-mildly alkaline basalts depending on the residence times within the crust. Hybrid magmas transported to the surface rapidly, favored by extensional post-collision regime, and produced mildly alkaline monogenetic volcanoes. Hybrid magmas interacted with the calc-alkaline magma chambers during the ascent to the surface suffered slight fractionation and crustal contamination due to relatively longer residence time compared to rapidly rising magmas. In this way they produced the mildly alkaline, transitional, and tholeiitic basaltic magmas. This model can explain the coexistence of a complete spectrum of q-normative, ol-hy-normative, and ne-normative monogenetic basalts with both subduction and within-plate signatures in the CAVP.     

Vulnerabilities to flood hazards among rural households in India

Natural Hazards - Flooding constitutes the most predominant natural disaster in India. The degree and causes of vulnerability to flood risk vary by society, geographical region and over time. The...