145 resultados para St. Peter sandstone


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This publication takes the form of a written version of my inaugural lecture, which was presented at Queen’s University Belfast on 10 March 2010. It is more personal and considerably more self-indulgent than would normally be acceptable in an article, with more of my own experiences and also my own references than would usually be considered proper. However, the bestowal of such a title as Professor of Island Geography is something of a marker of the maturity not just of myself but maybe also for island studies. After a section describing my path into island geography, the lecture deals with the negativities of islands and the seeming futility of studying them only then to identify a new or at least enhanced regard for islands as places with which to interact and to examine. Reference is made to islands throughout the world, but with some focus on the small islands off Ireland. The development of island studies as a discipline is then briefly described before the lecture concludes with reference to its title quotation on St Helena by considering that place’s islandness and how this affected/affects it in both the 17th and 21st centuries.

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We present the first marine reservoir age and Delta R determination for the island of St. Helena using marine mollusk radiocarbon dates obtained from an historical context of known age. This represents the first marine reservoir a.-c and Delta R determination in the southern Atlantic Ocean within thousands of kilometers of the island. The depletion of C-14 in the shells indicates a rather larger reservoir age for that portion of the surface Atlantic than models indicate. The implication is that upwelling old water along the Namibian coast is transported for a considerable distance, although it is likely to be variable on a decadal timescale. An artilleryman's button, together with other artifacts found in a midden, demonstrate association of the mollusk shells with a narrow historic period of AD 1815-1835.

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The problem of the long-term impact of historical fire on masonry is not clearly understood. Much research focuses on the damage that is caused by fire in isolation, and omits to investigate the subsequent exploitation of weaknesses inherited from fire events. Fire can, for example, cause significant physical, chemical and mineralogical change to sandstone, which may then be exploited by background environmental factors such as salt and freeze–thaw weathering. To explore this experimentally, blocks of Peakmoor Sandstone were subjected to a real fire (as well as lime rendering/removal and frost cycle pre-treatments), and their subsequent response to salt weathering cycles was monitored by weight loss and visual assessment of the pattern of surface damage. Results illustrate that the post-fire deterioration of sandstone is strongly conditioned by fracture networks and soot cover inherited from the fire. The exploitation of fractures can lead to spalling during salt weathering cycles — this takes place as granular dissagregation steadily widens cracks and salts concentrate and crystallise in areas of inherited weakness. Soot cover can have a profound effect on subsequent performance. It reduces surface permeability and can be hydrophobic in character, limiting salt ingress and suppressing decay in the short term. However, as salt crystals concentrate under the soot crust, detachment of this layer can occur, exposing fire-damaged stone beneath. Understanding the subsequent exploitation of stone exposed to fire damage by background environmental factors (for example, salt weathering/ temperature cycling) is key to the post-fire management of stone decay.

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