Showing papers by "Colin J. N. Wilson published in 1980"
TL;DR: In this paper, a series of experiments was carried out to review the process of fluidization for a number of particulate materials having various sorting and grain shape characteristics, and the up (increasing gas velocity) curve on a gas velocity/bed-pressure drop plot for a poorly sorted mixture of irregularly shaped particles was divided into three sections; nonexpanded, expanded, and segregating.
259 citations
TL;DR: In this paper, the authors look at certain ignimbrites which depart significantly from this conventional form in that a major part of them occurs as a thin layer mantling the landscape, resting on slopes as steep as 30°, and with an upper surface sensibly parallel with the underlying surface.
Abstract: Conventionally1, three important characteristics of ignimbrites are that they show a very pronounced tendency to pond in topographic depressions, possess a flat, horizontal or gently sloping upper depositional surface, and have a thickness generally between 10 and 1,000 m. The youngest major ignimbrite, that of 1912 in the Valley of Ten Thousand Smokes (Alaska)2–4 shows these characteristics well, being ponded in a valley 25 km long with a flat upper surface sloping down-valley at an average of 1.3°, and having an estimated thickness exceeding 100 m in places. AU three characteristics are commonly used as field criteria to distinguish ignimbrites from other pyroclastic rock bodies. Here we look at certain ignimbrites which depart significantly from this conventional form in that a major part of them occurs as a thin layer mantling the landscape, resting on slopes as steep as 30°, and with an upper surface sensibly parallel with the underlying surface. We have studied two examples, the 1,800-yr-old5 Taupo ignimbrite (New Zealand), and the 1,400-yr-old Rabual ignimbrite (New Britain)6,7. We also cite several others. These ignimbrites have a remarkably low aspect ratio. This ratio, previously applied to lava extrusions8,9, provides a useful means of quantifying the overall geometry of rock bodies. The ratio is that of average thickness to lateral spread; conveniently the latter is taken as the diameter of the circle which covers the same area as the rock body.
115 citations
TL;DR: A fine-depleted ignimbrite was found in the pyroclastic flow as discussed by the authors, which is largely depleted in the finer constituents and is clast-supported for all clasts exceeding about 2 mm in size.
Abstract: A new type of ignimbrite, a “fines-depleted ignimbrite,” is largely depleted in the finer constituents and is clast-supported for all clasts exceeding about 2 mm in size. Its formation is attributed to the loss of fine (mostly submillimetre-sized) vitric material from the pyroclastic flow, by an amount equal to about half of the original mass of the flow. This loss, the large size and high content of lithic clasts, and the thorough intermixing of carbonized vegetation are believed to indicate that the pyroclastic flow, at least in part, traveled turbulently. Turbulent flow was partly a consequence of a high flow velocity, for which there is independent evidence (the same flow climbed 1,500 m up a mountain 46 km from source), and was partly caused by the ingestion of forest and the resulting high throughput of gas in the flow head. The implication is that normal ignimbrite is generated by laminar flow, whereas turbulent flows generate the significantly different, fines-depleted variant.
62 citations
TL;DR: The Taupo eruption was a complex volcanic event that represents the most recent activity at the Taupo Volcanic Centre in the North Island of New Zealand as mentioned in this paper, and the average radiocarbon ages dates the eruption at ∼AD 130.
Abstract: The Taupo eruption was a complex volcanic event that represents the most recent activity at the Taupo Volcanic Centre1 in the North Island of New Zealand. The average2 of many radiocarbon ages dates the eruption at ∼AD 130. The records of ancient China and Rome refer to events in ∼AD 186 of the type which follow a major volcanic eruption, and we present here reasons for considering that these events were due to the Taupo eruption, and that the true date of the eruption is ∼AD 186.
59 citations
01 Apr 1980
TL;DR: The aureole material that formed an annulus of corrugated terrain surrounding Olympus Mons is considered to be the product of mass movement as mentioned in this paper, and the scarp at the mountain's foot formed as a result of this massive removal of material from the volcano's outer flanks.
Abstract: The aureole materials that form an annulus of corrugated terrain surrounding Olympus Mons are considered to be the product of mass movement. The scarp at the mountain's foot formed as a result of this massive removal of material from the volcano's outer flanks. This interpretation is supported by a comparison of the amount of material originally available before scarp formation, and the present volume of aureole materials. On the basis of distribution, surface textures and theoretical considerations it is considered that the aureole was produced by a series of megaslides, rather than by a flow mechanism. Production of the megaslides may have been assisted by a period of widespread melting of permafrost.
53 citations
3 citations
01 Jan 1980
TL;DR: The aureole material that formed an annulus of corrugated terrain surrounding Olympus Mons is considered to be the product of mass movement as discussed by the authors, and the scarp at the mountain's foot formed as a result of this massive removal of material from the volcano's outer flanks.
Abstract: The aureole materials that form an annulus of corrugated terrain surrounding Olympus Mons are considered to be the product of mass movement. The scarp at the mountain's foot formed as a result of this massive removal of material from the volcano's outer flanks. This interpretation is supported by a comparison of the amount of material originally available before scarp formation, and the present volume of aureole materials. On the basis of distribution, surface textures and theoretical considerations it is considered that the aureole was produced by a series of megaslides, rather than by a flow mechanism. Production of the megaslides may have been assisted by a period of widespread melting of permafrost.
1 citations