5. Making and breaking volcanoes

2020 ◽  
pp. 74-86
Author(s):  
Michael J. Branney ◽  
Jan Zalasiewicz
Keyword(s):  
Drainage Systems ◽  
Shield Volcanoes ◽  
Monogenetic Volcanoes ◽  
Scoria Cones ◽  
Shallow Reservoirs ◽  
Internal Architecture

‘Making and breaking volcanoes’ addresses how volcanoes are constructed and denuded and explains the shape of volcanoes and their internal architecture, including the differences between scoria cones, tuff rings, maars, and dome fields, shield volcanoes, and stratocones. Some volcanoes (‘monogenetic’ volcanoes) erupt just once, whereas others (‘polygenetic’ volcanoes) may continue erupting intermittently for millions of years. When sufficient magma is rapidly expelled from the shallow reservoirs beneath the volcano the overlying ground is left unsupported and collapses, creating a large topographic basin known as a caldera. As the caldera founders, its steep sides, formed so abruptly, are unstable and collapse inwards as a series of landslides. Tall volcanoes tend to collapse sideways in giant landslides, then grow and collapse again. Rain and meltwater also wears away volcanoes, forming lahars and floods, and choking drainage systems.

Chapter 5.1a Northern Victoria Land: volcanology

2021 ◽  
pp. M55-2018-60
Author(s):  
John L. Smellie ◽  
Sergio Rocchi
Keyword(s):  
Thermal Regime ◽  
Middle Miocene ◽  
Ice Sheet ◽  
Volcanic Group ◽  
Prevailing Paradigm ◽  
Shield Volcanoes ◽  
Victoria Land ◽  
Glacial Periods ◽  
Scoria Cones ◽  
Source Of Information

AbstractNeogene volcanism is widespread in northern Victoria Land, and is part of the McMurdo Volcanic Group. It is characterized by multiple coalesced shield volcanoes but includes a few relatively small stratovolcanoes. Two volcanic provinces are defined (Hallett and Melbourne), with nine constituent volcanic fields. Multitudes of tiny monogenetic volcanic centres (mainly scoria cones) are also scattered across the region and are called the Northern Local Suite. The volcanism extends in age between middle Miocene (c. 15 Ma) and present but most is <10 Ma. Two centres may still be active (Mount Melbourne and Mount Rittmann). It is alkaline, varying between basalt (basanite) and trachyte/rhyolite. There are also associated, geographically restricted, alkaline gabbro to granite plutons and dykes (Meander Intrusive Group) with mainly Eocene–Oligocene ages (52–18 Ma). The isotopic compositions of the plutons have been used to infer overall cooling of climate during the Eocene–Oligocene. The volcanic sequences are overwhelmingly glaciovolcanic and are dominated by ‘a‘ā lava-fed deltas, the first to be described anywhere. They have been a major source of information on Mio-Pliocene glacial conditions and were used to establish that the thermal regime during glacial periods was polythermal, thus necessitating a change in the prevailing paradigm for ice-sheet evolution.

Distribution of monogenetic volcanism along the Cameroon Line

2021 ◽  
Author(s):  
Christoph Schmidt ◽  
Christian Laag ◽  
Jörn Profe
Keyword(s):  
Spatial Organization ◽  
Volcanic Eruptions ◽  
Volcanic Field ◽  
Monogenetic Volcanism ◽  
Area Of Interest ◽  
Short Period ◽  
Volcanic Fields ◽  
Monogenetic Volcanoes ◽  
Spatio Temporal ◽  
Scoria Cones

&lt;p&gt;Volcanic eruptions may constitute a severe threat for local communities and their infrastructure. Important information as to the prediction of future eruption sites and the likelihood of activity can be obtained by analysis of spatio-temporal eruption pattern in an area of interest. The fact that monogenetic volcanoes, unlike polygenetic ones, erupt only once (within a geologically short period) at a certain spot and then volcanic activity jumps to another spot, renders a quantitative, probabilistic assessment of eruptive cycles challenging. In other words, the purely temporal risk assessment relevant for polygenetic volcanism has to be supplemented by a spatial dimension in case of monogenetic volcanic fields to allow for a combined spatio-temporal forecast.&lt;/p&gt;&lt;p&gt;While the eruption history of many stratovolcanoes along the Cameroon Line (CL) in Central Africa is comparatively well studied, only fragmentary data exists on the distribution and timing of monogenetic volcanism (mainly scoria cones and maars), presumably associated with Quaternary timescales. Here, we undertake an initial step in closing this gap and present for the first time a map of monogenetic volcanic features for most parts of the CL. Scoria cones and maars were identified by their characteristic morphologies using a combination of field knowledge, digital elevation models and satellite imagery. More than ~1300 scoria cones and 41 maars were detected and divided into eight monogenetic volcanic fields (MVF), as defined by the convex hull of the outermost vents: Bioko, Mt. Cameroon, Kumba, Tombel Graben (including Mt. Manengouba), Noun, Oku, Adamawa, and Biu (Nigeria). However, due to the rugged topography in the Oku volcanic field and the difficulty of identifying volcanic features remotely, the number of mapped scoria cones appears rather incomplete.&lt;/p&gt;&lt;p&gt;While the delineation of individual MVF bears an inherent subjective moment, statistical analyses of the primary dataset clearly shows that the mean nearest neighbour distance increases from &lt;1 km to ~2 km from the oceanic sector (Bioko, Mt. Cameroon) in the southwest towards the continental part in the northeast (Adamawa, Biu). Correspondingly, the areal density of monogenetic features decreases along this gradient by about one order of magnitude from &gt;0.2 km&lt;sup&gt;-2&lt;/sup&gt; (southwest) to 0.02 km&lt;sup&gt;-2&lt;/sup&gt; (northeast). This finding is in general agreement with prior geochronological results, indicating increased Quaternary activity towards the central and oceanic part of the CL (e.g., Njome and de Wit, 2014). Tests for the spatial organization of monogenetic volcanoes using the Geological Image Analysis Software (GIAS, v2; Beggan and Hamilton, 2010) revealed that the vents in all MVF are clustered (98% credible interval), thus allowing inferences to be drawn on the tectonic control of (future) eruption locations.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Beggan, C., Hamilton, C.W., 2010. New image processing software for analyzing object size-frequency distributions, geometry, orientation, and spatial distribution. Computers &amp; Geosciences 36, 539-549.&lt;/p&gt;&lt;p&gt;Njome, M.S., de Wit, M.J., 2014. The Cameroon Line: Analysis of an intraplate magmatic province transecting both oceanic and continental lithospheres: Constraints, controversies and models. Earth-Science Reviews 139, 168-194.&lt;/p&gt;

Ultrastructural investigations of MDL 19,660-induced effects on the canine platelet and megakaryocyte

1990 ◽  
Vol 48 (3) ◽  
pp. 374-375
Author(s):  
D.E. Loudy ◽  
J. Sprinkle-Cavallo ◽  
J.T. Yarrington ◽  
F.Y. Thompson ◽  
J.P. Gibson
Keyword(s):  
Antidepressant Drug ◽  
Beagle Dogs ◽  
Long Term Effects ◽  
Short Term ◽  
Platelet Counts ◽  
Toxicological Studies ◽  
Induced Aggregation ◽  
Internal Architecture

Previous short term toxicological studies of one to two weeks duration have demonstrated that MDL 19,660 (5-(4-chlorophenyl)-2,4-dihydro-2,4-dimethyl-3Hl, 2,4-triazole-3-thione), an antidepressant drug, causes a dose-related thrombocytopenia in dogs. Platelet counts started to decline after two days of dosing with 30 mg/kg/day and continued to decrease to their lowest levels by 5-7 days. The loss in platelets was primarily of the small discoid subpopulation. In vitro studies have also indicated that MDL 19,660: does not spontaneously aggregate canine platelets and has moderate antiaggregating properties by inhibiting ADP-induced aggregation. The objectives of the present investigation of MDL 19,660 were to evaluate ultrastructurally long term effects on platelet internal architecture and changes in subpopulations of platelets and megakaryocytes.Nine male and nine female beagle dogs were divided equally into three groups and were administered orally 0, 15, or 30 mg/kg/day of MDL 19,660 for three months. Compared to a control platelet range of 353,000- 452,000/μl, a doserelated thrombocytopenia reached a maximum severity of an average of 135,000/μl for the 15 mg/kg/day dogs after two weeks and 81,000/μl for the 30 mg/kg/day dogs after one week.

ECOLOGICAL STATUS AND RECONSTRUCTION OF RYAZAN REGION MELIORATION SYSTEM

1970 ◽  
pp. 33-37
Author(s):  
P. N. Vanyushin ◽  
A. V. Kuzin ◽  
А. А. Pavlov ◽  
А. V. Nefedov ◽  
N. А. Ivannikova
Keyword(s):  
Russian Federation ◽  
Agricultural Land ◽  
Cultural Landscapes ◽  
Land Reclamation ◽  
Ecological Status ◽  
Economic Feasibility ◽  
Drainage Systems ◽  
Viable Systems ◽  
The Russian Federation ◽  
Technical Operation

The article analyzes the current state of the irrigation and drainage systems of the Ryazan region. It is shown that the lack of technical operation of the drainage network led to its failure and failure to perform its functions. Irrigation, in spite of the fact that it gives stability in the years of droughts due to aging and the dismantling of machinery and equipment is not carried out. It is shown that for the reconstruction and / or modernization of irrigation and drainage systems it is necessary on the basis of inventory to determine the environmentally optimal and economically viable systems, their parts and structures that require rehabilitation, reconstruction and / or modernization. The decision to reconstruct may include not only the ameliorative system as a whole, but also some part of it, for example, a canal, pipeline or a separate hydraulic structure, taking into account the justification of economic feasibility. In dry periods, for the Meshcherskaya lowland and areas with peat soils, it is necessary to provide for land-reclamation systems for dual regulation of soil moisture, which reduces the possibility of peat ignition and the spread of fire. It should be borne in mind that the reconstruction of land-reclamation systems has its specific features, which include: socio-economic (increasing the productivity of agricultural land, obtaining additional income, creating modern infrastructure, increasing employment, living conditions, labor, etc.) ; ecological (creation of cultural landscapes, ensuring their ecological sustainability, prevention of land degradation processes, improvement of recreational conditions, elimination of waterlogging, flooding, salinization, erosion, etc.). Reclamation activities are carried out in compliance with the requirements of land, water, forestry legislation of the Russian Federation, as well as the legislation of the Russian Federation on the protection of the environment, on the subsurface, on the plant world and on the animal world.

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