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Volcano - (a) Processes of Volcanism

(Strombolian, Plinian, Lava Flows, Pyroclastic Flows)

Strombolian Fire Fountain

Explosive Plinian Eruption

Lava Flows

 

Pyroclastic Flow Eruption

 

Volcano - (b) More Volcanoes

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1979 Re-Classification of Volcanic Activity - PLEASE NOTE!

In the past volcanoes were classified as being either Active,Dormant or Extinct.

This classification however, did not take into account those supposedly 'extinct', or even 'unknown' volcanoes which "come-to-life" every so often; sometimes killing hundreds and causing widespread destruction to property.

This term 'Active' was originally based on whether a volcano had erupted within 'historic times', or whether it had ongoing solfataric and fumarolic activity.

Yet 'historic times' varies from a few hundred years in the Pacific Area to over three thousand years in the Mediterranean, and whether or not a volcanic region is able to sustain fumaroles may depend on the residual heat in underground bodies of rock, the flow of the water table and the prevailing climate. It is difficult to sustain fumarolic activity in an arid desert region.

Finally the term 'Active' took no account of whether the volcano was actually erupting or not.

In 1979, following a UNESCO meeting of World Volcanic Experts in Indonesia, it was proposed that a more useful and meaningful classification should be adopted, to replace the outdated and unscientific classification that has perpetuated itself in the scientific literature for far too long.

 

VOLCANOES SHOULD NOW BE CLASSIFIED AS BEING EITHER LIVE OR DEAD!

 

LIVE VOLCANOES have a high probability of erupting at some time in the future: such as the familiar POLYGENETIC VOLCANOES [which erupt many times] of Mt.Vesuvius, Mt.Etna, Mt.St.Helens and Fujiyama [Huzi San].

 

DEAD VOLCANOES have a very low probability of ever erupting again: Examples are those POLYGENETIC VOLCANOES which have long since ceased to function and are so old that their Roots are now exposed through erosion, MONOGENETIC VOLCANOES [which erupt only once] - such as the parasitic cinder cones that occur on the sides of larger POLYGENETIC volcanoes, and the basaltic cinder cones that erupt only once in highly active areas; here, on cessation of activity the cinder cone volcano is DEAD but the underlying volcanic field which gave rise to it is LIVE and may spawn many more MONOGENETIC eruptions in the future. eg:- The Auckland and Central Mexican LIVE VOLCANIC FIELDS.

 

Volcanoes are now classified as being either LIVE or DEAD; with one subdivision:-

LIVE volcanoes that are not erupting are DORMANT LIVE VOLCANOES

LIVE volcanoes that are erupting are ACTIVE LIVE VOLCANOES

Volcanoes that will never erupt again are DEAD VOLCANOES

 

The outdated term "EXTINCT" has little or no use in Modern Volcanology and is best discarded.

Refs:-

Booth,B.; 1979. Assessing Volcanic Risk. Journal of the Geological Society of London, Vol. 136, pp331-40.

Booth,B.; Croasdale,R.; Walker,G.P.L. 1978. A Quantitative Study of Five Thousand Years of Volcanism on San Miguel, Azores. Philosophical Transactions of the Royal Society (London), Part A, Vol. 288, pp. 271-319.

Crandell,D.R.; Booth,B.; Kusumadinata,K.; Shimozuru,D.; Walker,G.P.L.; & Westercamp,D. 1984. Source-book for volcanic-hazards zonation. Natural Hazards 4. Unesco.

Lirer,L.; Pescatore,T.; Booth,B.; Walker,G.P.L. 1973. Two Plinian Pumice-fall Deposits from Somma-Vesuvius, Italy. Geological Society of America Bulletin, Vol. 84, pp. 759-72.

Walker,G.P.L.; 1974. Volcanic Hazards and the Prediction of Volcanic Eruptions, pp23-41. Geological Society of London. (Misc. Paper, 3.)


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