Mid-Holocene lateral collapse of Antuco volcano (Chile): debris avalanche deposit features,emplacement dynamics,and impacts     

Romero  Jorge E.  Moreno  Hugo  Polacci  Margherita  Burton  Mike  Guzmán  Danny 《Landslides》2022,19(6):1321-1338

Antuco (37.4°S, 71.4°W; Chile) is a dominantly basaltic stratovolcano whose original?~?3300 m altitude main cone experienced a catastrophic sector collapse at?~?7.1 cal ka BP, producing a volcanic debris avalanche deposit (VDAD) with hummocky surface and?~?6.4 km³ of volume. We carried out geological studies of its debris avalanche deposit, which was distributed to the W and displays a longitudinal facies transformation from edifice’s megablocks and block to mixed facies in distal areas (up to 25 km from the scar). Our observations support the behavior of the avalanche beginning as a translational slide, and then as plug flow when confined within the Laja River valley. Clay abundance and high content of hydrothermally altered material may suggest active participation of water; flow velocities are estimated to?~100 m s^?1. We primarily identify the steep-sided flanks of the cone, and hydrothermal alteration promoted the edifice instability, while basement seismogenic structures may have ultimately triggered the landslide. Subsequent landslide-led events include the transformation of the volcanic activity with explosive eruptions producing a sequence of dilute pyroclastic density currents (PDCs) ending?~3.4 ky BP, and extensive lava effusion rapidly reconstructing the collapsed edifice. Moreover, the Antuco VDAD also blocked the natural output of the Laja Lake, increasing its level by?~200 m and then triggering cataclysmic outburst floods by dam rupture, preserved as high-energy alluvial beds with ages between 2.8 and 1.7 ky BP. The Antuco constitutes an excellent example of a critical chain of events initiated by a stratovolcano lateral collapse and warns for detailed hazard investigations to better comprehend its related impacts.

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Estimating aquifer recharge in fractured hard rock: analysis of the methodological challenges and application to obtain a water balance (Jaisamand Lake Basin,India)   总被引：1，自引：0，他引：1  

Melissa M. Rohde  W. Mike Edmunds  David Freyberg  Om Prakash Sharma  Anupma Sharma 《Hydrogeology Journal》2015,23(7):1573-1586

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Quantification of the gas mass emitted during single explosions on Stromboli with the SO2 imaging camera     

Toshiya Mori  Mike Burton 《Journal of Volcanology and Geothermal Research》2009,188(4):395-400

We performed measurements using an SO₂ imaging camera of the SO₂ gas mass emitted during five discrete explosive events on Stromboli volcano on 3 October 2006. The SO₂ gas mass released during discrete explosions was 15–40 kg per explosion, producing 3–8% of the total daily SO₂ gas emission, demonstrating that in terms of gas flux Strombolian explosions are a second-order phenomenon compared with quiescent degassing. Using the typical gas composition measured with OP-FTIR allows us to determine the total gas mass released during an explosion as 360–960 kg with a volume of 1500–4100 m³ at 1 bar. At the probable source pressure of gas slug formation of 75 MPa this gas amount would occupy a volume equivalent to a sphere with a radius of 0.8–1 m, comparable with estimates of Stromboli's conduit geometry.  相似文献   

Natural aggregates in the performance and durability of concrete: physical characteristics     

Peter G. Fookes  Mike J. Walker 《Geology Today》2011,27(4):141-148

The production of rock aggregates for construction is the largest of the extractive industries in Britain. Natural aggregates form the main component, by volume, in the manufacture of concrete but the part played by aggregates in the durability and performance aspects of concrete is still only moderately understood. This feature summarizes the main characteristics of common aggregate in concrete, especially those leading to cracking and deterioration. Physical and mechanical causes of concrete cracking are of immense importance but are omitted from the following. The feature expands on the earlier one: ‘Concrete: a man‐made rock?’ (Geology Today, 2010, v.26, n.2). To follow is another that will continue the story by looking at chemical reactivity in concretes.  相似文献   

Gully erosion in Mangatu Forest,New Zealand,estimated from digital elevation models     

R. C. Derose  Basil Gomez  Mike Marden  N. A. Trustrum 《地球表面变化过程与地形》1998,23(11):1045-1053

The methodology and errors involved in determining the amount of sediment produced during two (19·5 and 33·2 year) periods by 11 (c. 0·01 − >0·20 km²) gullies within a 4 km² area in the headwaters of the Waipaoa River basin, New Zealand, using sequential digital elevation models are described. Sediment production from all gullies within the study area was 0·99 ± 0·03 × 10⁶ t a⁻¹ (2480 ± 80 t ha⁻¹ a⁻¹) during the period from 1939 to 1958. It declined to 0·62 ± 0·02 × 10⁶ t a⁻¹ (1550 ± 50 t ha⁻¹ a⁻¹) during the period from 1958 to 1992, when many of the smaller gullies were stabilized by a programme of afforestation, which commenced in 1960. Both figures are very high by global standards. The two largest (the Tarndale and Mangatu) gully complexes together generated 73 and 95 per cent of the sediment in the specified time periods, but the latter amount is equivalent to only c. 5 per cent of the total annual sediment load of the Waipaoa River. © 1998 John Wiley & Sons, Ltd.  相似文献   

Fractal dimensions of suspended solids in streams: comparison of sampling and analysis techniques     

Dirk H. de Boer  Mike Stone 《水文研究》1999,13(2):239-254

Fluvial suspended sediment typically consists of a variety of complex, composite particles referred to as flocs. Floc characteristics are determined by factors such as the source, size and geochemical properties of the primary particles, chemical and biological coagulation processes in the water column and shear stress and turbulence levels in the stream. Studies of floc morphology have used two contrasting methods of sampling and analysis. In the first method, particles settle on a microscope slide and are observed from below using an inverted microscope. The second method uses filtration at no or low vacuum and particles deposited on the filter are observed with a microscope. Floc morphology can be quantified using fractal dimensions. The aims of the present study were to examine the effect of the two sampling methods on the fractal dimensions of particle populations, and to evaluate for each method how well the fractal dimensions at the various sampling sites reflect basin conditions. Suspended solids were collected in triplicate on inverted microscope slides and on 0·45 μm Millipore HA filters in two southern Ontario streams with contrasting riparian zones during a minor runoff event resulting from the melt of a freshly fallen snowpack. An image analysis system was used to determine area, longest axis and perimeter of particles. The morphology of the particle population of each sample was characterized using four fractal dimensions (D, D₁, D₂ and D_K). Systematic differences in fractal dimensions obtained with the two methods were observed. For the settling method, outlines of larger particles were frequently blurred because of the distance between the focal plane (the top of the inverted microscope slides) and the plane of the particle outline. In this method, the blurring of large particles can cause an increase in the projected area and length of the particle. The effect on the particle perimeter is unpredictable because it depends on the amount of detail lost through blurring and its effect on the apparent increase in particle size. Because of blurring, D and D₁ tend to be systematically lower for the settling method, whereas the net effect on D₂ is unpredictable. Particle size distributions derived from settling are typically coarser because small, low density particles may remain in the water column and all particles may not deposit on the slides. This loss of fines results in systematically lower D_K values for the settling method compared with the filtration method. Fractal dimensions and particle size distributions obtained with the filtration method were sensitive to and clearly indicated differences between drainage basins and between sites within each basin. These differences were explained by basin characteristics and conditions. Fractal dimensions and particle size distributions obtained with the settling method were less sensitive to drainage basin characteristics and conditions, which limits their usefulness as process indicators. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

The influence of basement faults on local extension directions: Insights from potential field geophysics and field observations     

Anindita Samsu  Alexander R. Cruden  Mike Hall  Steven Micklethwaite  Steven W. Denyszyn 《Basin Research》2019,31(4):782-807

Complex arrays of faults in extensional basins are potentially influenced by pre‐existing zones of weakness in the underlying basement, such as faults, shear zones, foliation, and terrane boundaries. Separating the influence of such basement heterogeneities from far‐field tectonics proves to be challenging, especially when the timing and character of deformation cannot be interpreted from seismic reflection data. Here we aim to determine the influence of basement heterogeneities on fault patterns in overlying cover rocks using interpretations of potential field geophysical data and outcrop‐scale observations. We mapped >1 km to meter scale fractures in the western onshore Gippsland Basin of southeast Australia and its underlying basement. Overprinting relationships between fractures and mafic intrusions are used to determine the sequence of faulting and reactivation, beginning with initial Early Cretaceous rifting. Our interpretations are constrained by a new Early Cretaceous U‐Pb zircon isotope dilution thermal ionization mass spectrometry age (116.04 ± 0.15 Ma) for an outcropping subvertical, NNW‐SSE striking dolerite dike hosted in Lower Cretaceous Strzelecki Group sandstone. NW‐SE to NNW‐SSE striking dikes may have signaled the onset of Early Cretaceous rifting along the East Gondwana margin at ca. 105–100 Ma. Our results show that rift faults can be oblique to their expected orientation when pre‐existing basement heterogeneities are present, and they are orthogonal to the extension direction where basement structures are less influential or absent. NE‐SW to ENE‐WSW trending Early Cretaceous rift‐related normal faults traced on unmanned aerial vehicle orthophotos and digital aerial images of outcrops are strongly oblique to the inferred Early Cretaceous N‐S to NNE‐SSW regional extension direction. However, previously mapped rift‐related faults in the offshore Gippsland Basin (to the east of the study area) trend E‐W to WNW‐ESE, consistent with the inferred regional extension direction. This discrepancy is attributed to the influence of NNE‐SSW trending basement faults underneath the onshore part of the basin, which caused local re‐orientation of the Early Cretaceous far‐field stress above the basement during rifting. Two possible mechanisms for inheritance are discussed—reactivation of pre‐existing basement faults or local re‐orientation of extension vectors. Multiple stages of extension with rotated extension vectors are not required to achieve non‐parallel fault sets observed at the rift basin scale. Our findings demonstrate the importance of (1) using integrated, multi‐scale datasets to map faults and (2) mapping basement geology when investigating the structural evolution of an overlying sedimentary basin.  相似文献   

Dr Donald S McLusky – an appreciation and thanks from ECSS     

Eric Wolanski Ivan Valiela  Mike Elliott 《Estuarine, Coastal and Shelf Science》2010

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Managed realignment as compensation for the loss of intertidal mudflat: A short term solution to a long term problem?     

Krysia Mazik  Will Musk  Oliver Dawes  Katya Solyanko  Sue Brown  Lucas Mander  Mike Elliott 《Estuarine, Coastal and Shelf Science》2010

Intertidal mudflats are critical to the functional ecology of estuaries yet large areas are being lost as a result of land claim, erosion and coastal squeeze. This study examines whether managed realignment (at Paull Holme Strays, Humber estuary) can realistically achieve compensation for the loss of intertidal mudflat in the long term. Typical estuarine species quickly colonised the site with the total number of species recorded from the site as a whole being almost equal to that in the reference area within one year. Comparable biomass between the two areas was achieved after 2 years. However, organism abundance remains an order of magnitude lower within the realignment site compared to outside. Community structure within the realignment has changed from one characterised by terrestrial/freshwater organisms and early colonising species to one composed of typically estuarine species. However, the developing benthic communities only represent those typical of the estuary in areas of low elevation and high inundation frequency. Rapid accretion has favoured saltmarsh colonisation in much of the realignment site and this is expected to increase as accretion proceeds with invertebrate colonisation being inhibited by increasing elevation. Hence, realignment to restore intertidal mudflats can only be a short term solution in sites of high tidal elevation and in a dynamic and turbid estuary with high natural accretion rates, such as the Humber.  相似文献   

Contemporary initiatives on the future of the International Whaling Commission     

Mike Iliff 《Marine Policy》2010

In his term as Chairman of the International Whaling Commission between 2006 and 2009, Dr BillHogarth championed a process for finding a way forward for the IWC. In parallel with, and in places intertwined with the Hogarth Initiative, a number of other initiatives attempting to move the IWC forward have been proposed by a range of stakeholders; both governments and NGOs. This paper traces the more important suggestions, commenting on their likelihood of success.  相似文献