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Summer camps are an $18 billion industry while providing over 14,000 individual programs in the United States in 2015. Camp counselors, like other outdoor workers, are at risk of occupational solar exposure. Occupational solar exposure increases an individual's lifetime accumulation of solar radiation, leading to skin damage and higher rates of skin cancer. This study fills a gap in the research about the sun protection behaviors of camp counselors and their attitude towards protecting themselves and the campers in their care. Overall, counselors did not achieve experts' recommendations for sun protection. The findings suggest that summer camps are not taking adequate steps to protect their staff from a known workplace hazard. The Occupational Safety and Health Administration appears to currently not be holding summer camps accountable. The findings have implications for hiring, training, and risk management practices for the summer camp industry.

Oceanic transform faults are seismically and tectonically active plate boundaries.sup.1 that leave scars--known as fracture zones--on oceanic plates that can cross entire ocean basins.sup.2. Current descriptions of plate tectonics assume transform faults to be conservative two-dimensional strike-slip boundaries.sup.1,3, at which lithosphere is neither created nor destroyed and along which the lithosphere cools and deepens as a function of the age of the plate.sup.4. However, a recent compilation of high-resolution multibeam bathymetric data from 41 oceanic transform faults and their associated fracture zones that covers all possible spreading rates shows that this assumption is incorrect. Here we show that the seafloor along transform faults is systemically deeper (by up to 1.6 kilometres) than their associated fracture zones, in contrast to expectations based on plate-cooling arguments. Accretion at intersections between oceanic ridges and transform faults seems to be strongly asymmetric: the outside corners of the intersections show shallower relief and more extensive magmatism, whereas the inside corners have deep nodal basins and seem to be magmatically starved. Three-dimensional viscoplastic numerical models show that plastic-shear failure within the deformation zone around the transform fault results in the plate boundary experiencing increasingly oblique shear at increasing depths below the seafloor. This results in extension around the inside corner, which thins the crust and lithosphere at the transform fault and is linked to deepening of the seafloor along the transform fault. Bathymetric data suggest that the thinned transform-fault crust is augmented by a second stage of magmatism as the transform fault intersects the opposing ridge axis. This makes accretion at transform-fault systems a two-stage process, fundamentally different from accretion elsewhere along mid-ocean ridges. Oceanic transform faults are systemically deeper than their associated fracture zones, owing to the plate boundary experiencing increasingly oblique shear at increasing depths below the seafloor., Author(s): Ingo Grevemeyer [sup.1] , Lars H. Rüpke [sup.1] , Jason P. Morgan [sup.2] , Karthik Iyer [sup.1] [sup.3] , Colin W. Devey [sup.1] Author Affiliations: (1) GEOMAR Helmholtz Centre [...]

Delamination of lower continental lithosphere is known to have occurred under different tectonic settings. However, its fate in the mantle is poorly understood. By analyzing global seismic models, we find that most of likely lithosphere that delaminated during the Cenozoic and Mesozoic is preserved in the mantle transition zone, especially beneath North America and Africa. Numerical experiments indicates that delaminated lithosphere can remain stagnant in the mantle transition zone for tens of millions of years, followed by its potential sinking into the lower mantle or re‐rising to shallower depths depending on its density, the Clapeyron slope of the spinel‐to‐post‐spinel phase change and increase in mantle viscosity at ∼660–1,000 km depths. Re‐ascent occurs when delaminated lithosphere is reheated so that its effective density becomes lower than its surrounding ambient mantle after ∼100 Myr. Delaminated fragments can also potentially be mobilized by underlying global mantle flow to move horizontally away from plume regions. Plain Language Summary: The phenomenon of lower lithospheric delamination has been recognized in various tectonic settings, but the ultimate fate of these delaminated fragments within the mantle remains poorly known. From global seismic tomographic models, we gain first‐order constraints on the potential locations of geologically recent (<250 Ma) delaminated lithosphere, particularly in regions distant from subduction zones. A significant portion of Cenozoic and Mesozoic delaminated lithosphere appears to still be sequestered within the mantle transition zone, with pronounced concentrations beneath the Mesozoic and Cenozoic locations of North America and Africa. Numerical simulations further corroborate the hypothesis that these fragments of delaminated lithosphere can remain stagnant within the mantle transition zone over these geologically interesting timescales. Delaminated lithosphere can also re‐rise or move horizontally depending on underlying global mantle flow. Key Points: Seismic tomographic models provide first‐order constraints on the location of recent delaminated lithosphere in the upper and mid‐mantleDelaminated lithosphere can remain stagnant in the mantle transition zone for tens to hundreds of millions of yearsDepending on underlying mantle flow, delaminated lithosphere can also eventually warm and rise, or even move horizontally [ABSTRACT FROM AUTHOR]

Determining the mechanisms responsible for intraplate volcanism ‐ such as slab devolatilization melting versus active mantle plumes ‐ remains a challenge. The greater South China Sea (SCS) region has experienced extensive intraplate Cenozoic volcanism across areas including Hainan, Southeast Indochina, northern Borneo, the northern SCS, and the post‐spreading SCS basin. The prevalence of volcanism distributed widely across this region prompts fundamental questions about the key geodynamic processes driving such diverse magmatic activities. In this study, we elucidate the mantle transition zone (MTZ) discontinuities in this region using SS precursors, which helps to overcome the sparse seismic coverage due to its predominantly oceanic setting. We collected over 16,000 high‐quality seismograms that sample the upper mantle and MTZ beneath this region from global earthquakes and stations. After correcting for the effects of shallow crustal variations and upper mantle heterogeneity on traveltimes of SS phases and their precursors, we unveil lateral variations in the MTZ boundaries (d410 and d660) and intricate features of the mid‐MTZ reflectors (S520S). Significant MTZ thinning and normal S520S waveforms beneath Hainan provide compelling evidence for mantle upwelling through the MTZ. Conversely, the evident splitting of S520S beneath the northern SCS, Southeast Indochina, and northern Borneo, all characterized by stagnant subducted slabs, indicates that the volcanism in these regions likely originated from a mechanism distinct from the active upwelling beneath Hainan. Dehydration melting attributed to devolatilizing stagnant slabs in the MTZ is a potential cause for Cenozoic volcanism in these regions. Plain Language Summary: Determining the causes of volcanic activity far from tectonic plate boundaries remains a challenge. The greater South China Sea region experienced widespread volcanism during the Cenozoic era, prompting questions about the driving geological processes behind this phenomenon. This study investigated the boundaries of the mantle transition zone (MTZ) beneath the region using seismic wave analysis of over 16,000 seismic recordings. By analyzing the travel times of signals reflected from the MTZ boundaries and internal reflectors, lateral variations in the structure of the MTZ boundaries and internal features were revealed. Beneath Hainan, thinning of the MTZ and normal waveforms of the internal MTZ reflector suggest upwelling of hot mantle material through the MTZ, likely causing the surface volcanism. In contrast, beneath the northern South China Sea, Southeast Indochina, and northern Borneo, the distorted waveforms of signals from the internal MTZ reflector indicate a different mechanism. These latter regions contain ancient, subducted slabs present in their MTZs. Dehydration melting, caused by the release of water from these stagnant slabs within the MTZ, is a potential cause of the Cenozoic volcanism in these areas, distinct from the mantle upwelling observed beneath Hainan. Key Points: SS precursors from the mantle transition zone (MTZ), notably the S520S, provide insights into mantle dynamics beneath the greater South China Sea (SCS) regionEvidence of MTZ thinning and normal S520S waveform beneath Hainan suggests active mantle upwelling through the MTZThe S520S splitting beneath areas with stagnant subducted slabs indicates a possible magmatic origin through flux melting [ABSTRACT FROM AUTHOR]

Continents are formed by the amalgamation of numerous micro-terranes and island arcs, so they have spatially varying lithosphere strengths. The crème brûlée (CB) model and the jelly sandwich (JS) model have been commonly used to describe continental lithosphere strength–depth variations. Depending on the strength of the continental lower crust, the CB and JS models can be further subdivided into two subclasses in which the I subclass (CB-I and JS-I) and II subclass (CB-II and JS-II), respectively, have a strong or weak lower crust. During the continental collision, lithosphere deformation is the byproduct of the comprehensive interaction of multiple terranes. Here we used 2-D thermomechanical numerical models that contain three continental terranes to systematically explore the effects of terranes with various strengths on continental deformation and studied the effects of different rheological assumptions on terrane deformation. We found four types of lithosphere deformation patterns: collision, subduction, thickening and delamination, and replacement. These simulation patterns are seen in observed deformation patterns and structures in East Asia, suggesting they are likely to be naturally occurring modes of intracontinental orogenesis. [ABSTRACT FROM AUTHOR]

Delamination of the continental lithospheric mantle is well recorded beneath several continents. However, the fate of the removed continental lithosphere has been rarely noted, unlike subducted slabs reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5 horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500 to 700 km depths beneath former Gondwana, with slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone and mid-mantle above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2 to 4 × 106 km³, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high-wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa. [ABSTRACT FROM AUTHOR]

Continents are formed by the amalgamation of numerous micro-terranes and island arcs, so they have spatially varying lithosphere strengths. The Crεave;me brȗlée (CB) model and the Jelly sandwich (JS) model have been commonly used to describe continental lithosphere strength-depth variations. Depending on the strength of continental lower crust, the CB and JS models can be further subdivided into two subclasses, in which the I subclass (CB-I and JS-I) and II subclass (CB-II and JS-II) respectively have a strong or weak lower crust. During continental collision, lithosphere deformation is the byproduct of the comprehensive interaction of multiple terranes. Here we used 2-D thermo-mechanical numerical models that contain three continental terranes to systematically explore the effects of terranes with various strengths on continental deformation, and studied the effects of different rheological assumptions terrane deformation. We find four types of lithosphere deformation patterns: collision, subduction, thickening and delamination, and replacement. Lithosphere structures, especially local pre-existing weaknesses, also have nonnegligible influences on lithosphere deformation. These simulation patterns are seen in observed deformation patterns and structures in East Asia, suggesting they are likely to be naturally occurring modes of intracontinental orogenesis. [ABSTRACT FROM AUTHOR]

Continents are formed by the amalgamation of numerous micro-terranes and island arcs, so they have spatially varying lithosphere strengths. The Crème br?lée (CB) model and the Jelly sandwich (JS) model have been commonly used to describe continental lithosphere strength-depth variations. Depending on the strength of continental lower crust, the CB and JS models can be further subdivided into two subclasses, in which the I subclass (CB-I and JS-I) and II subclass (CB-II and JS-II) respectively have a strong or weak lower crust. During continental collision, lithosphere deformation is the byproduct of the comprehensive interaction of multiple terranes. Here we used 2-D thermo-mechanical numerical models that contain three continental terranes to systematically explore the effects of terranes with various strengths on continental deformation, and studied the effects of different rheological assumptions terrane deformation. We find four types of lithosphere deformation patterns: collision, subduction, thickening and delamination, and replacement. Lithosphere structures, especially local pre-existing weaknesses, also have nonnegligible influences on lithosphere deformation. These simulation patterns are seen in observed deformation patterns and structures in East Asia, suggesting they are likely to be naturally occurring modes of intracontinental orogenesis. [ABSTRACT FROM AUTHOR]

Text messaging has gained widespread popularity in higher education as a communication tool and as a means of engaging students in the learning process. In this study we report on the use of text messaging in a large, year-one introductory chemistry module where students were encouraged to send questions and queries to a dedicated text number both during lectures and at other times when support with module material was required. Questions were answered either verbally during the lecture itself, at a subsequent tutorial or via a reply back to the student's mobile phone. SMS texting was also used as a rapid system for communicating results of a class test following a peer assessment exercise. With knowledge only of the student's registration number a text message can be sent to a dedicated text number and then forwarded by mail filtering rules to the recipient student's mobile phone. Finally, text messaging was evaluated as an in-class voting system to conduct short multiple choice quizzes on material being covered in a bioanalytical chemistry lecture without the need for bespoke handsets or specialist software. Students commented favourably on the use of text messaging in these contexts. (Contains 1 table and 4 figures.)

Hydrothermal flow at oceanic spreading centres accounts for about ten per cent of all heat flux in the oceans (1,2) and controls the thermal structure of young oceanic plates. It also influences ocean and crustal chemistry, provides a basis for chemosynthetic ecosystems, and has formed massive sulphide ore deposits throughout Earth's history. Despite this, how and under what conditions heat is extracted, in particular from the lower crust, remains largely unclear. Here we present high-resolution, whole-crust, two- and three-dimensional simulations of hydrothermal flow beneath fast-spreading ridges that predict the existence of two interacting flow components, controlled by different physical mechanisms, that merge above the melt lens to feed ridge-centred vent sites. Shallow on-axis flow structures develop owing to the thermodynamic properties of water, whereas deeper off-axis flow is strongly shaped by crustal permeability, particularly the brittle-ductile transition. About 60 per cent of the discharging fluid mass is replenished on-axis by warm (up to 300 degrees Celsius) recharge flow surrounding the hot thermal plumes, and the remaining 40 per cent or so occurs as colder and broader recharge up to several kilometres away from the axis that feeds hot (500-700 degrees Celsius) deep-rooted off-axis flow towards the ridge. Despite its lower contribution to the total mass flux, this deep off-axis flow carries about 70 per cent of the thermal energy released at the ridge axis. This combination of two flow components explains the seismically determined thermal structure of the crust and reconciles previously incompatible models favouring either shallower on-axis (3-5) or deeper off-axis hydrothermal circulation (6-8)., The fast-spreading East Pacific Rise (EPR) at 9°N is one of the best-studied ridge sections worldwide. Multichannel seismic studies between 9°N and 13°N image a nearly continuous sub-axial melt lens [...]

The forearc region remains key in understanding the dynamics of convergent plate tectonics. This study focuses on the mechanisms governing tectonic processes within the overriding plate forearc which spans from the trench to the volcanic arc at two key and relatively well studied regions: the Japan Trench and the Middle America Trench offshore SE Costa Rica. We address the questions that have arisen concerning material input into the plate boundary, whether by subduction, accretionary prism formation, or tectonic erosion. In the Japan Trench case study, while tectonic accretion occurs near the trench axis, significant forearc subsidence suggests net material removal, possibly through tectonic erosion that has transferred material to the subducting slab. Debate surrounds the mechanism driving forearc subsidence, with recent studies proposing extensional tectonism as a possible mechanism to exclude subduction erosion. However, seismic evidence challenges this hypothesis, as normal faults indicative of forearc extension are not prominent. Moreover, a quantitative mass-balance analysis fails for the forearc if extensional tectonics rather than tectonic erosion is assumed to have predominantly shaped the margin. The spatio-temporal progression of subsidence across the forearc is further explored; this indicates that peak subduction erosion has occurred beneath the lower slope. The Middle America Trench in SE Costa Rica has also been extensively studied with several drilling expeditions, with particular focus on the area where the aseismic Cocos Ridge is subducting beneath the Caribbean plate. Here the subduction of topographic relief has been traditionally viewed as a process that enhances subduction erosion. Recent studies have challenged this perspective, suggesting instead that subducting topography might lead to net accretion to the margin through various mechanisms. Ocean drilling expeditions provide valuable data on sedimentary successions and forearc tectonic evolution. These drilling data have been not always used to the best of their capacity, which has led to significant discrepancies between drilling-based inferences and seismic interpretations, in particular regarding the presence and nature of unconformities within the forearc sediments. Borehole observations strongly favor the inference that inboard the Cocos Ridge a large amount of subsidence has occurred, linked to recent subduction erosion beneath this forearc. [ABSTRACT FROM AUTHOR]

During the last 50 Ma, the East Asian continent has been a zone of massive continental collision and lithospheric deformation. While the consequences of this for Asian surface and lithospheric deformation have been intensively studied over the past 4 decades, the relationships between lithospheric deformation and underlying asthenospheric flow have been more difficult to constrain. Here we present a high resolution 3-D azimuthal anisotropy model for the northeastern Tibetan Plateau and its eastward continuation based on surface-wave tomography and shear-wave splitting measurements. This model shows that eastward lateral flow of asthenosphere beneath the northeastern Tibetan Plateau is being blocked by thick Ordos and Sichuan cratonic keels. The damming effect of these keels induces flow to first rotate around the Ordos keel and then transition into strong east-west flow beneath the thinner lithosphere that forms the lithospheric suture between the two cratonic keels. We further find that asthenosphere flow directions can differ from those of overlying lithosphere, with the asthenosphere neither being passively dragged by overlying lithosphere, nor being able to drag the overlying plate to mimic its subsurface flow. Finally, the region of eastward-channeled asthenospheric flow from Tibet underlies a belt of stronger intracontinental deformation in eastern China. [ABSTRACT FROM AUTHOR]