A gigantic Bezymianny-type event at the beginning of modern volcan Popocatepetl

The history of volcan Popocatepetl can be divided into two main periods: the formation of a large primitive volcano — approximatively 30 km wide — on which is superimposed a modern cone (6–8 km in diameter and 1700m high). A major event of Bezymianny type marks the transition between these two dissimilar periods.The activity of the primitive volcano was essentially effusive and lasted several hundred thousands of years. The total volume of products ejected by the volcano is of the order of 500–600 km³. Its last differentiated magmas are dacitic.A gigantic debris flow (D.F.) spread on the southern side is related to the Bezymianny-type event which destroyed the summit area of the ancient edifice. An elliptical caldera ( 6.5 × 11 km wide) was formed by the landslide. Its deposits, with a typical hummocky surface, cover 300 km² for a volume of 28–30 km³. Numerous outcrops belonging to this debris flow show “slabs” of more or less fractured and dislocated rocks that come from the primitive volcano. These deposits are compared to two studied debris flows of similar extent and volume: the Mount Shasta and Colima's D.F.This eruption takes a major place in the volcanologic and magmatic history of Popocatepetl: pyroclastic products of surge-type with “laminites” and crude layers, ashflows, and pumiceous airfall layers are directly related to this event and begin the history of the modern volcano probably less than 50,000 years ago. In addition, a second andesitic and dacitic phase rose both from the central vent — forming the basis of modern Popo — and from lateral vents.The terminal cone is characterized by long periods of construction by lava flows alternating with phases of destruction, the duration of these episodes being 1000 to 2000 years. The cone is composed of two edifices: the first, volcan El Fraile, began with effusive activity and was partly destroyed by three periods of intense explosive activity. The first period occurred prior to 10.000 years B.P., the second from 10.000 to 8000 years B.P. and the third from 5000 to 3800 years B.P. Each period of destruction shows cycles producing collapsing pyroclastic flows or nuées of the St Vincent-type related to the opening of large craters, plinian air-fall deposits and minor lava flows. The second edifice, the summit Popo, produced lava flows until 1200 years B.P. and since that time, entered into an explosive period. Two cataclysmic episodes, each including major pyroclastic eruptions, occurred 1200 and 900–1000 years ago. During the Pre-Hispanic and historic times effusive activity was restricted entirely to the summit area alternating with plinian eruptions. Nevertheless, despite the quiet appearance of the volcano, the last period of pyroclastic activity which started 1200 years ago may not have ended and can be very dangerous for the nearby populations.     

Quantum theory and geography

The application of Newtonian physics to complex fluvial and atmospheric processes is suggested to be inadequate. In the 1970s a number of exciting cosmological theories were developed which formed the basis for models of the early expansion of the Universe. Since these models derive from Einstein's ten gravitational field equations (rather than Newton's single equation) they possess a deep subtlety and may well be of interest to geographers in the explanation of fundamental patterns.     

Intrinsic oxygen fugacity measurements on seven chondrites,a pallasite,and a tektite and the redox state of meteorite parent bodies

Intrinsic oxygen-fugacity (fO₂) measurements were made on five ordinary chondrites, a carbonaceous chondrite, an enstatite chondrite, a pallasite, and a tektite. Results are of the form of linear log $\text{f}\text{O}{}_2\text{?}\text{1}\text{T}$ plots. Except for the enstatite chondrite, measured results agree well with calculated estimates by others.The tektite produced fO₂ values well below the range measured for terrestrial and lunar rocks. The lowpressure atmospheric regime that is reported to follow large terrestrial explosions, coupled with a very high temperature, could produce glass with fO₂ in the range measured.The meteorite Salta (pallasite) has low fO₂ and lies close to Hvittis (E6). Unlike the other samples, results for Salta do not parallel the iron-wüstite buffer, but are close to the fayalite-quartz-iron buffer in slope.Minor reduction by graphite appears to have taken place during metamorphism of ordinary chondrites. fO₂ values of unequilibrated chondrites show large scatter during early heating suggesting that the constituent phases were exposed to a range of fO₂ conditions. The samples equilibrated with respect to fO₂ in relatively short time on heating. Equilibration with respect to fO₂ in ordinary chondrites takes place between grades 3 and 4 of metamorphism. Application of P ? T ? fO₂ relations in the system C-CO-CO₂ indicates that the ordinary chondrites were metamorphosed at pressures of 3–20 bars, as it appears that they lay on the graphite surface.A steep positive thermal gradient in a meteorite parent body lying at the graphite surface will produce thin reduced exterior, an oxidized near-surface layer, and an interior that is increasingly reduced with depth; a shallow thermal gradient will produce the reverse. A body heated by accretion on the outside will have a reduced exterior and oxidized interior. Meteorites from the same parent body clearly are not required to have similar redox states.     

Transformation of coordinates between two horizontal geodetic datums

The following topics are discussed in this paper: the geocentric coordinate system and its different realizations used in geodetic practice; the definition of a horizontal geodetic datum (reference ellipsoid) and its positioning and orientation with respect to the geocentric coordinate system; positions on a horizontal datum and errors inherent in the process of positioning; and distortions of geodetic networks referred to a horizontal datum. The problem of determining transformation parameters between a horizontal datum and the geocentric coordinate system from known positions is then analysed. It is often found necessary to transform positions from one horizontal datum to another. These transformations are normally accomplished through the geocentric coordinate system and they include the transformation parameters of the two datums as well as the representation of the respective network distortions. Problems encountered in putting these transformations together are pointed out.     

The complex decision-making of climate-induced relocation: adaptation and loss and damage

Climate change is increasingly challenging the ability of millions of people to sustain livelihoods as the places where they live become uninhabitable. The relocation of populations as individuals, households, and communities within countries and across international borders demonstrates the complexity of climate change impacts. Looking at the literature, some researchers argue that relocation caused by climate change can be an effective strategy to adapt to localized changes, whereas others argue that the movement away from ones' homeland is more neatly captured in the climate change lexicon as ‘loss and damage’. We argue here that the relocation of people as a result of the impacts of climate change can be both adaptation and loss and damage. Drawing on examples from Alaska and Kiribati, we show that dividing this issue between the two concepts is unhelpful in resolving key issues around the types of appropriate support for these transitions to sustain and protect livelihoods and to open up possibilities for self-determined futures.

Policy Relevance

Climate-induced relocation poses a significant challenge for the populations affected as well as the government agencies tasked with providing technical assistance and funding. At present, policies and institutional frameworks have not yet been developed to accommodate these challenges, despite the urgent need to do so. When the relocation of populations can be planned, participatory, and people centred, then it can be an adaptation strategy that will protect people from the permanent loss of land and livelihoods. If these movements are decided, driven, managed, and undertaken by those affected, then there is the potential for the relocation to also be a transformative opportunity for people to respond to the impacts of climate change, and sustain their livelihoods and possibly even improve certain livelihood outcomes. However, these relocations also cause significant loss and damage. The extent of the loss and damage will partly depend on the ability to have these relocations planned and ensure that human rights protections are embedded in institutional frameworks. The article shares a series of lessons and learnings that are of policy relevance at a variety of scales.     

Galactic evolution and star counts in the milky way

A model of population synthesis for our Galaxy is used to estimate the constraints imposed by photometric and astrometric star counts. We construct a statistical method to compute the degree of compatibility of the model with the data in the form of a multidimensional functionf(V, B-V, U-B, ). We apply the method to the determination of the star formation history in the Galaxy from Schmidt plates towards the anticentre. Although the presently available data do not allow us to draw firm conclusions, we show that the same kind of data with a slightly better photometric accuracy and with proper motions would give new constraints on the past star formation rate of the Galaxy.     

Slope‐to‐basin stratigraphic evolution of the northwestern Great Bahama Bank (Bahamas) during the Neogene to Quaternary: interactions between downslope and bottom currents deposits

Multichannel high‐resolution seismic data along the northwestern margin of the Great Bahama Bank (GBB), Bahamas, detail the internal geometry and depositional history of a Neogene‐Quaternary carbonate slope‐to‐basin area. The stratigraphic architecture through this period evolves from (i) a mud‐dominated slope apron during the Miocene, (ii) a debris‐dominated base‐of‐slope apron during the Late Pliocene and then (iii) return to a slope apron with very short prograding clinoformal aprons during the Pleistocene. This geometric evolution was broadly constrained by the development of the Santaren Drift by bottom current since the Langhian. The drift expands along the northwestern GBB slope, forming a continuous correlative massive feature that shows successive phases of growth and retreat and influenced the downslope sediments distribution. Indeed, Late Pliocene deposits are confined into the moat, forming a strike‐continuous coarse debrites belt along the mid‐slope, preventing their free expansion into the basin. The occurrence of basinal drift that operated since 15 Ma showed a significant upslope growth around 3.6 Ma and is interpreted as resulting from the closure of the Central American Seaway which also coincides with a global oceanographic re‐organization and climate changes in the Northern Hemisphere.     

Tramper perspectives on New Zealand's Great Walks in a time of transition

‘Great Walks’ are highly managed multi‐day experiences established within New Zealand's national parks. We examine their history and promotion asking ‘How have the contexts for recreational walking in the New Zealand wilderness changed?’ and ‘How are these changes regarded by trampers as practitioners of backcountry walking?’ To address these questions, we draw on 703 responses to an online survey. We note a mixed regard for Great Walks among trampers. Some consider the wilderness experience as undermined by the popularity of these branded experiences while others note that they cater for a range of users, despite high costs reducing effective accessibility.