Deep sea mining concerns the extraction of poly-metallic nodules, cobalt-rich crusts and sulphide deposits from the ocean floor. The exploitation of these resources will result in adverse ecological effects arising from the direct removal of the substrate and, potentially, from the formation of sediment plumes that could result in deposition of fine sediment on sensitive species or entrainment of sediment, chemicals and nutrients into over-lying waters. Hence, identifying the behaviour of deep-sea sediment plumes is important in designing mining operations that are ecologically acceptable. Here, we present the results of novel in situ deep sea plume experiments undertaken on the Tropic seamount, 300 nautical miles SSW of the Canary Islands. These plume experiments were accompanied by hydrographic and oceanographic field surveys and supported by detailed numerical modelling and high resolution video settling velocity measurements of the in situ sediment undertaken in the laboratory. The plume experiments involved the controlled formation of benthic sediment plumes and measurement of the plume sediment concentration at a specially designed lander placed at set distances from the plume origin. The experiments were used as the basis for validation of a numerical dispersion model, which was then used to predict the dispersion of plumes generated by full-scale mining. The results highlight that the extent of dispersion of benthic sediment plumes, resulting from mining operations, is significantly reduced by the effects of flocculation, background turbidity and internal tides. These considerations must be taken into account when evaluating the impact and extent of benthic sediment plumes.Background. There is increasing global concern over the long-term availability of secure and adequate supplies of critical raw materials, known as E-tech elements, which have an essential contribution to emerging 'green' technologies 1 . These E-tech elements are present (in different concentrations and combinations) in poly-metallic nodules on the ocean floor and cobalt-rich crusts on seamounts 2 . Additionally, seafloor massive sulphide deposits contain economically attractive concentrations of a variety of minerals including copper, gold, silver and zinc 3 . Plans to extract these minerals involve a seafloor harvester, creating sediment disturbance through its motion across the sea bed, cutting of the substrate, collection of the minerals, discharge of uneconomic sediment after processing and, potentially, discharge of over-burden covering buried deposits 4-7 . Such operations will remove substrate (and any ecology bound to, or buried within, the substrate), and also generate turbidity plumes that may result in deposition of sediment onto sensitive species in the near to far-field and/or entrainment of sediment, nutrients and chemicals into over-lying waters.A review of previous sediment resuspension experiments 8 describes the various deep sea plume experiments undertaken to date 9-13 . These experiments mainly consisted of towed ha...

Summary Detailed mapping reveals many structures, unrelated to the slight regional tilting, folding and faulting, that are determined not by deep-seated movements but by disturbances that are demonstrably of superficial origin. These structures include cambers, gulls, dip-and-fault structure and valley bulges. As a result of these movements dissected Inferior and Great Oolite strata are lowered vertically to the extent of 100 feet or more, so that they swathe the hill tops and valley sides. The causal processes of this camber structure include sub-surface erosion and valleyward outflow of the underlying Lias. Gulls are widened joints in the camber filled with material from above. They usually* trend parallel to the strike of the cambered strata and may attain a width of 40 yards. Step-faulting of similar trend is commonly associated with advanced cambering. The throw of each fault in this " dip-and-fault " structure is compensated for by steep downslope dips (up to 40°) in the inter-fault blocks. Valley bulges comprise a variety of upward displacements of the strata that are confined to the valleys and are due to differential loading of the incompetent Lias. Their origin and mode of development are discussed in relation to the physiography of the area and the fundamental part played by the Lias clay. The economic significance of the structures in the exploitation of ironstone and in water supply are briefly considered and reference is made to analogous structures in other areas.

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Summary The paper deals with an area of over 600 square miles falling largely within the drainage basins of the rivers Nene and Welland. Formations present comprise a succession from the Lower Lias to the Oxford Clay and Pleistocene-Recent drifts. Six-inch mapping, supplemented by numerous borehole records, discloses differences between the present and the sub-boulder-clay topography. The significance of these differences is discussed. Relics of the surface on which the present cycle of erosion was initiated are preserved as bevels on the solid formation. This surface, which falls from 750 feet O.D. in the west to below 250 feet in the east, is believed to have been tilted toward the North Sea basin. Study of the stages of river diversion and capture provides strong evidence of an original W.-E. consequent drainage. The controlling effect of structure on river development is clearly shown. Certain lines of drainage are believed to have existed as subsequent streams before the start of the present cycle of erosion. The origin of the large-scale superficial structures of the region is reconsidered. It is claimed that they were produced under periglacial conditions. The authors suggest that an important part was played by perennially frozen ground in the physiographic evolution of the region.

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