Channelized lava flows at the East Pacific Rise crest 9°–10°N : the importance of off-axis lava transport in developing the architecture of young oceanic crust

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 6 (2005): Q08005, doi:10.1029/2005GC000912.Submarine lava flows are the building blocks of young oceanic crust. Lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava, the characteristics of the eruption, and the topography it encounters. The resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50–500 m of the oceanic crust. We have mapped and measured numerous submarine channelized lava flows at the East Pacific Rise (EPR) crest 9°–10°N that reflect the high-effusion-rate and high-flow-velocity end-member of lava eruption and transport at mid-ocean ridges. Channel systems composed of identifiable segments 50–1000 m in length extend up to 3 km from the axial summit trough (AST) and have widths of 10–50 m and depths of 2–3 m. Samples collected within the channels are N-MORB with Mg# indicating eruption from the AST. We produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins. Modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0.4 to 4.7 × 103 m3/s, and modeled shear rates help explain the surface morphology variation. We suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off-axis region (1–3 km) and produces the layer 2A thickening that is observed at fast and superfast spreading ridges. In addition, the rapid, high-volume-flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the EPR. We find that high concentrations of channelized lava flows correlate with local, across-axis ridge morphology indicative of an elevated magma budget. Additionally, in locations where channelized flows are located dominantly to the east or west of the AST, the ridge crest is asymmetric, and layer 2A appears to thicken over a greater distance from the AST toward the side of the ridge crest where the channels are located.This work was supported by NSF grant OCE-9819261 (to H.S., M.A.T., and D.J.F.) as well as the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Penzance Endowed Discretionary Fund

Evaluation of external errors relating to portable use of Digital Image Correlation

A strength of Digital Image Correlation (DIC) is the potential manoeuvrability of the system. It is noted, however, that by increasing the range of locations in which analysis is carried out, the number of uncontrollable variables grow. For example, when testing outside there may be changes to ambient lighting or there may be external vibrations occurring and these effects may alter measurement accuracy. The overall objective of this research is to quantify errors associated with the use of DIC in different (non-ideal) locations and, associated with this, to find methods of limiting the effect of the potential error sources. The reference test sample is a thin-walled shell into which defects can be introduced at specified locations, thus disturbing the local strain field. A portable test rig, which makes use of an internal vacuum, to cause a pressure differential on the component, has been designed and deployed to explore the potential of using DIC as a method of non-destructive evaluation. Preliminary results have been conducted in a laboratory setting to ensure that the strain data correlate with finite element analysis. Following from initial experimentation, successive investigations into the effects of possible external error sources have been conducted. These include: ground vibrations, increased airflow and changes in ambient lighting. Each experiment is repeated five times to allow for random error of the testing process. DIC has been shown to be a powerful tool in identifying the strain perturbation associated with the presence of defects. Initial results indicate that environment conditions have the potential to lead to perturbation of results, but that these may be identified and minimised and/or corrected if care is taken

Life story work in health and social care: systematic literature review

The aim of this paper is to review the literature on life story work in health and social care practice. Life story work as an intervention has been used with a number of health and social care clients, such as children people with learning disabilities, older people on medical wards and with older people who have dementia. It may help challenge ageist attitudes and assumptions, be used as a basis for individualized care, improve assessment, assist in transitions between different care environments, and help to develop improved relationships between care staff and family carers. However, to date there has been no attempt to collate the findings from published accounts. A systematic search of the literature on life story work was conducted in February 2004, using nursing, medical and social science databases and a combination of thesaurus and free text search terms. This revealed over 1000 publications; the use of carefully constructed inclusion and exclusion criteria identified 51 relevant items. Fourteen were subsequently selected and reviewed using a set of reflective critical appraisal questions. A range of methodological approaches has been adopted to explore the use of life story work with no one specific methodology prevailing. The work has been most frequently used with older people and people with a learning disability and life story books are the most common approach. Staff perceptions of life story work have been explored, but patient and carer views are less frequently reported. The findings of the studies are discussed in broad themes, offering some tentative recommendations for using life story work in practice. Evidence on the use of life story work is immature, leading to the recommendation for more research. Although appraising literature from a range of approaches is complex, there are some potentially far-reaching benefits of life story work in health and social care practice