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I.—The Mechanism of Volcanic Action, being the Opening Address to Section III (Vulcanology) of the International Geographical Congress

Published online by Cambridge University Press:  01 May 2009

H. J. Johnston-Lavis
H. J. Johnston-Lavis
Affiliation:
Royal University of Naples.
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Extract

In a discussion of this kind it is advisable to be as concise as possible, eliminating minor details, so as to give prominence to the main outlines of any theory one holds. This communication, which the Council of the Ninth International Congress of Geography have honoured me by asking me to address to you, I propose to put into the form of a ‘credo’. To this I shall add a few fundamental facts upon which, my reasoning was based, leaving minor ones for discussion at greater leisure elsewhere. For convenience I propose to divide my theory into two sections. In the first I shall review what may be conveniently called deep volcanic action, and in the second that group of phenomena that occur when igneous matter nearly reaches the surface or actually finds an exit thereon. Unfortunately, in the first case I am obliged to rely on hypotheses and deductions, whereas in the second section, that of superficial volcanic action, there are a number of fundamental facts and observations upon which to base speculation, and to which. I propose to draw your attention.

Type
Original Articles
Information
Geological Magazine , Volume 6 , Issue 10 , October 1909 , pp. 433 - 443
Copyright
Copyright © Cambridge University Press 1909

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References

page 434 none 1 Davison, C.: “On the Distribution of Strain in the Earth's Crust resulting from Secular Cooling, etc.” (Phil. Trans. R.S., 1887, vol. clxxviii)Google Scholar; “Note on the Relation between the Size of a Planet and the Rate of Mountain Building on its Surface” (Phil. Mag., Nov., 1887); “On the Straining of the Earth resulting from Secular Cooling” (Phil. Mag., Feb., 1896); “On Secular Straining of the Earth” (Geol. Mag., 05, 1889, Dec. III, Vol. VI, No. 299, p. 220)Google Scholar. Reade, T. Mellard: The Origin of Mountain Ranges, 1886Google Scholar. See also Johnston-Lavis, H. J.: “The Extension of the Mellard Reade and C. Davison Theory of Secular Straining of the Earth to the explanation of the Deep Phenomena of Volcanic Action” (Geol. Mag., 06, 1890, Dec. III, Vol. VII, pp. 246–9).CrossRefGoogle Scholar

page 435 note 1 These blocks are quite different to the blocks referred to by some recent writers on terrestrial mechanics.

page 437 note 1 ProfessorHobbs, , Ninth International Congress of Geography, 1908.Google Scholar

page 438 note 1 “The Geology of Monte Somma and Vesuvius”: Q.J.G.S., 1884, vol. xl, pp. 35–119.Google Scholar

page 438 note 2 In my paper “On the Fragmentary Ejecta of Volcanos” (Proc. Geol. Assoc., vol. ix, pp. 421–32 and 3 figs.)Google Scholar I divided such ejecta into three classes. Essential ejecta are those materials that issue in a fluid state, and consist either of the volatile constituents or the magma in which these were contained, that produced the particular emission in question. Accessory ejecla consist of the older volcanic materials of the same vent torn away, expelled, and mixed with the essential ejecta of an eruption. Accidental ejecta consist of either volcanic materials from other centres, or sedimentary or other rocks of the sub-volcanic platform, also torn out, expelled, and mixed with the two before-mentioned ejecta.

page 441 note 1 I use H2O not to assume any special physical state of that substance. I also refer to it specially as being the principal volatile material of igneous magma; but I fully appreciate the salts and gases derived from their decomposition, as likewise the rarer materials that were acquired by and can be separated from igneous rocks by a high temperature, to which Monsieur Brun and others have furnished us with such interesting details by their studies.