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Ice shelves restrain flow from the Greenland and Antarctic ice sheets. Climate-ocean warming could force thinning or collapse of floating ice shelves and subsequently accelerate flow, increase ice discharge and raise global mean sea levels. Petermann Glacier (PG), northwest Greenland, recently lost large sections of its ice shelf, but its response to total ice shelf loss in the future remains uncertain. Here, we use the ice flow model Úa to assess the sensitivity of PG to changes in ice shelf extent, and to estimate the resultant loss of grounded ice and contribution to sea level rise. Our results have shown that under several scenarios of ice shelf thinning and retreat, removal of the shelf will not contribute substantially to global mean sea level (<1 mm). We hypothesize that grounded ice loss was limited by the stabilization of the grounding line at a topographic high ~12 km inland of its current grounding line position. Further inland, the likelihood of a narrow fjord that slopes seawards suggests that PG is likely to remain insensitive to terminus changes in the near future.
Drag at the bed and along the lateral margins are the primary forces resisting flow in outlet glaciers. Simultaneously inferring these parameters is challenging since basal drag and ice viscosity are coupled in the momentum balance, which governs ice flow. We test the ability of adjoint-based inverse methods to infer the slipperiness coefficient in a power-law sliding law and the flow-rate parameter in the constitutive relation for ice using a regularization scheme that includes coefficients weighted by surface strain rates. Using synthetic data with spatial variations in basal drag and ice rheology comparable to those in West Antarctic Ice Streams, we show that this approach allows for more accurate inferences. We apply this method to Bindschadler and MacAyeal Ice Streams in West Antarctica. Our results show relatively soft ice in the shear margins and spatially varying basal drag, with an increase in drag with distance upstream of the grounding line punctuated by localized areas of relatively high drag. We interpret soft ice to reflect a combination of heating through viscous dissipation and changes in the crystalline structure. These results suggest that adjoint-based inverse methods can provide inferences of basal drag and ice rheology when regularization is informed by strain rates.
To conduct international comparisons of self-reports, collateral reports, and cross-informant agreement regarding older adult psychopathology.
We compared self-ratings of problems (e.g. I cry a lot) and personal strengths (e.g. I like to help others) for 10,686 adults aged 60–102 years from 19 societies and collateral ratings for 7,065 of these adults from 12 societies.
Data were obtained via the Older Adult Self-Report (OASR) and the Older Adult Behavior Checklist (OABCL; Achenbach et al., 2004).
Cronbach’s alphas were .76 (OASR) and .80 (OABCL) averaged across societies. Across societies, 27 of the 30 problem items with the highest mean ratings and 28 of the 30 items with the lowest mean ratings were the same on the OASR and the OABCL. Q correlations between the means of the 0–1–2 ratings for the 113 problem items averaged across all pairs of societies yielded means of .77 (OASR) and .78 (OABCL). For the OASR and OABCL, respectively, analyses of variance (ANOVAs) yielded effect sizes (ESs) for society of 15% and 18% for Total Problems and 42% and 31% for Personal Strengths, respectively. For 5,584 cross-informant dyads in 12 societies, cross-informant correlations averaged across societies were .68 for Total Problems and .58 for Personal Strengths. Mixed-model ANOVAs yielded large effects for society on both Total Problems (ES = 17%) and Personal Strengths (ES = 36%).
The OASR and OABCL are efficient, low-cost, easily administered mental health assessments that can be used internationally to screen for many problems and strengths.
Compulsory admission procedures of patients with mental disorders vary between countries in Europe. The Ethics Committee of the European Psychiatric Association (EPA) launched a survey on involuntary admission procedures of patients with mental disorders in 40 countries to gather information from all National Psychiatric Associations that are members of the EPA to develop recommendations for improving involuntary admission processes and promote voluntary care.
The survey focused on legislation of involuntary admissions and key actors involved in the admission procedure as well as most common reasons for involuntary admissions.
We analyzed the survey categorical data in themes, which highlight that both medical and legal actors are involved in involuntary admission procedures.
We conclude that legal reasons for compulsory admission should be reworded in order to remove stigmatization of the patient, that raising awareness about involuntary admission procedures and patient rights with both patients and family advocacy groups is paramount, that communication about procedures should be widely available in lay-language for the general population, and that training sessions and guidance should be available for legal and medical practitioners. Finally, people working in the field need to be constantly aware about the ethical challenges surrounding compulsory admissions.
Non-surface mass balance is non-negligible for glaciers in Iceland. Several Icelandic glaciers are in the neo-volcanic zone where a combination of geothermal activity, volcanic eruptions and geothermal heat flux much higher than the global average lead to basal melting close to 150 mm w.e. a−1 for the Mýrdalsjökull ice cap and 75 mm w.e. a−1 for the largest ice cap, Vatnajökull. Energy dissipation in the flow of water and ice is also rather large for the high-precipitation, temperate glaciers of Iceland resulting in internal and basal melting of 20–150 mm w.e. a−1. The total non-surface melting of glaciers in Iceland in 1995–2019 was 45–375 mm w.e. a−1 on average for the main ice caps, and was largest for Mýrdalsjökull, the south side of Vatnajökull and Eyjafjallajökull. Geothermal melting, volcanic eruptions and the energy dissipation in the flow of water and ice, as well as calving, all contribute, and thus these components should be considered in mass-balance studies. For comparison, the average mass balance of glaciers in Iceland since 1995 is −500 to −1500 mm w.e. a−1. The non-surface mass balance corresponds to a total runoff contribution of 2.1 km3 a−1 of water from Iceland.
How are volcanoes born, in which way do they live, and why and when, eventually, do they become extinct? More specifically, why are there any polygenetic central volcanoes at all? Why is the volcanism not simply evenly distributed through the volcanic zone or field? There are certainly volcanic areas where the volcanism is more or less evenly distributed – such as at fast-spreading ridges. But for most other volcanic areas one or more locations within the area dominates the volcanism, resulting in the formation of a specific central volcano. The central volcano erupts much more frequently than its surroundings and, therefore, normally forms an edifice. The edifice is a structure with a certain mechanical strength, most of which derives from the internal structure of the volcano. Later in the evolution of the volcano, it may form a collapse caldera, as well as being subject to lateral collapses, all of which affect its shape. When, eventually, the supply of magma to the volcano is cut off, it becomes extinct, that is, dies.
One of the main aims of the science of volcanology, and that of volcanotectonics in particular, is to understand volcanic unrest periods. By ‘understanding’ I mean that the signals coming from the volcano during the unrest can be interpreted in terms of plausible physical and chemical processes occurring inside the volcano. By volcanic ‘unrest’ we mean an increase in various physical and chemical signals, suggesting that associated processes within the volcano operate at different rates, intensities, or both. By interpreting the unrest period in terms of correct physical processes, there is a chance of assessing the volcanic hazard, namely the probability that the unrest period results in an eruption. Furthermore, when the understanding of the processes giving rise to the signals is accurate, not only the location of the eruption site but also the likely size (volume) of the eruption can be forecasted.
Field studies of volcanotectonic structures offer a way of understanding the processes that take place inside volcanoes before eruptions. Collapse calderas and some other large-scale structures are treated separately (Chapter 5), and here the focus is on sheet intrusions, sills, inclined (cone) sheets, and, in particular, dikes. Since they supply magma to most eruptions, it is important to make detailed and accurate observations and measurements of sheet intrusions in eroded sections of active and inactive (extinct) volcanoes. All the techniques described here apply equally well to inclined sheets, so that the term ‘dike’ in the present context also includes inclined sheets. Most of the techniques also apply to sills; the special aspects of field studies of sills are discussed at the end of the chapter. The observations and measurements provide a better understanding of how dikes propagate, the field conditions that encourage dike arrest, as well as the conditions that encourage their propagation to the surface to feed volcanic eruptions. The field data, when combined with geodetic and seismic monitoring data, can be used to test analytical, analogue, and numerical models on internal processes in volcanoes.
How does magma move or rise from its source chamber to the surface? More specifically, how does magma generate a path to the surface so as to supply magma to an eruption? Or, in general, under what conditions do dike-fed eruptions occur? While these questions have been briefly mentioned in some of the earlier chapters, they and the answers have not been discussed in detail. That I shall do in the present chapter. While magma moves through the crust by different mechanisms (e.g. as diapirs), the main mechanism is magma-driven fractures. The general name for all magma-driven fractures, once solidified, is sheet intrusions or sheets, which include dikes, inclined sheets, and sills. Unless stated otherwise, the theoretical discussion in this chapter applies equally to all these three types of sheets. Here, the focus is on mostly dikes, partly for the simple reason that dikes supply magma to most eruptions. For general theoretical considerations, dike denotes both subvertical dikes, regional and local, and commonly also inclined sheets, although in some instances a distinction will be made between these structures.
Volcanoes are of many types and behave in different ways. Different behaviour is partly because volcanoes are located in different tectonic environments. Many are associated with divergent plate boundaries, others with convergent plate boundaries, and some with transform-fault plate boundaries. In addition, there are volcanoes located within plate interiors, far from plate boundaries. To understand volcano behaviour with a view to being able to forecast volcanic eruptions we must use a variety of scientific techniques and approaches, primarily those of volcanotectonics. The main techniques and approaches for data collection, analysis, and interpretation are discussed in detail in later chapters, but they are briefly summarised here.
Volcanic (or volcano) earthquakes are those that occur inside volcanoes or close to them. The study of these earthquakes in volcanoes is commonly referred to as volcano seismology. Most earthquakes associated with volcanoes occur at comparatively shallow depths, normally of less than 10 km. They differ from other earthquakes at plate boundaries partly in that volcanic earthquakes commonly occur in swarms, that is, clusters in time and space of many comparatively small and similar-sized earthquakes. Volcanic earthquakes provide information about the state of stress in the volcano and of eventual magma-chamber rupture during unrest periods (e.g. Massa et al., 2016). They also indicate the location and, crudely, the size of magma chambers. When a dike (or an inclined sheet) is injected from a magma chamber, the formation of its propagation path (dike-fracture path) produces earthquakes. Thus, accurate monitoring of earthquakes during such events can be used to map out the propagation path of the dike and help assess the likelihood of the dike (or inclined sheet) reaching the surface, causing an eruption.
Polygenetic volcanoes, to a first approximation, behave as is they are elastic. When subject to loading such as magmatic excess pressure in a chamber or overpressure in a dike, the volcano deformation is, so long as the loading is small, roughly linear elastic. When related to pressure changes in the source chamber, the measured deformation is referred to as inflation when the volcano surface rises (during magma-pressure increase) and as deflation when the surface falls or subsides (during magma-pressure decrease). If the loading generates stresses that reach the strength of the rock, then fractures form or reactivate. Slip on shear fractures, that is, faults, commonly triggers earthquakes, which can be used to monitor the state of stress in the volcano as well as magma movement through dike or sheet propagation. Some stresses are sufficiently large to form or reactivate the boundary faults of grabens or the ring-faults of collapse calderas. Similarly, the stresses may result in lateral or sector collapses, that is, landslides. The earthquake activity in volcanoes is treated in Chapter 4, and vertical and lateral collapses in Chapter 5.
A magma chamber is the heart of every polygenetic volcano. Many, presumably most, polygenetic volcanoes have two magma chambers: one shallow crustal chamber and another deep-seated chamber, which we here refer to as a reservoir. Together, the reservoir and the shallow chamber constitute a double magma chamber. The complex interaction between the source reservoir and the chamber determines the frequency of injection of inclined sheets and dikes. Together with the mechanical layering and local stresses in the crustal segment, the double chamber also largely controls the frequency and sizes of eruptions in the volcano to which it supplies magma. We have learned that most shallow chambers evolve from sills and are located in the upper crust. The deep-seated reservoirs, by contrast, are normally located in the lower crust or upper mantle. If located in the crust, they may also evolve from sills; if located in the upper mantle, they may evolve as magma accumulations in regions of low potential energy. The accurate determination of the location of active magma chambers is generally difficult.