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This one day symposium was made possible by the substantial assistance given by the U.S. Army, Research and Development Group (Europe) and arranged by Dr. Hoyt Lemons, Chief Scientist. This is here gratefully acknowledged. Part of the grant has been used to subsidise this number of the Quarterly Journal of Engineering Geology devoted to the proceedings of the symposium. The symposium was organized by Dr. D. Brunsden, Mr. R. J. G. Edwards, Dr. J. N. Hutchinson and Mr. G. Walton.

Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 323-325. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.01

A wide variety of phenomena have been described as mudflows. In this paper these are reviewed and an attempt is made at a classification. It is hoped that in this way some clarification of the terminology can be achieved.

Aspects of mudflows discussed include their morphology, fabric and structures, their speeds, distribution and mechanisms of movement, their relation to climate and lithology and their importance in both the present and past environment. Methods of observing and instrumenting their behaviour, and techniques of forecasting and control are also dealt with. Finally, typical case records are given of the main types of mudflow identified.

Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 326. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.02
Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 329-338. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.03
Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 339-349. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.04

Mudflows or lahars are a common accompaniment of volcanism. Sometimes they are a direct consequence of an eruption, as when the contents of a crater lake are suddenly released, or when an explosive eruption generates a torrential rainstorm. At other times they are an indirect consequence, as when the disposition of a mantle of relatively impermeable ash increases run-off. The first kinds of mudflow can be very destructive, and rank a close second to the nuée ardente for the damage and loss of life they can cause.

Mudflows constitute 10 to 30% of the bulk of many volcanoes, particularly andesitic ones, and examples are known of mudflows which have travelled 100 km or more from their source. They are characterised by their poor sorting and lack of internal stratification, and they commonly contain very large lithic blocks and show a form of reverse grading. They have probably often been misidentified as agglomerates, but criteria are available to distinguish them from most other kinds of volcanic deposits (they lack the jig-saw structure of rock avalanche deposits, for instance); their closest affinities are with ignimbrites.

Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 351. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.05

Deposits ascribed to slope-dependent mass-transport mechanisms are not uncommon in the geological record. In terms of relative abundance, deposits of this type formed in subaerial environments are subordinate to those originating in subaqueous (and especially submarine) conditions. This difference results partly from the lower preservation potential of subaerial deposits but there is evidence that mechanisms of this type are both common and more effective in subaqueous environments.

Described fossil examples of subaerial mass-movement include mud and gravel flows associated with alluvial fans and the deposits of volcanic/pyroclastic origin known as lahars. Sediments of deformed or chaotic aspect, attributed to mass-movement under glacial or periglacial conditions, are widespread in the Pleistocene and early Holocene but are rarely recorded from older glacial episodes.

The lithified products of subaqueous mass-transport encompass a wide range of sedimentary environments, from fluvial through lacustrine and deltaic to the deep ocean floor. Such sediments also span the entire spectrum of behavioural categories, from elastic through plastic to viscous or fluid conditions. A new classification of subaqueous mass-transport deposits which is essentially descriptive but carries important genetic implications will be discussed, with examples.

Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 353. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.06
Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 355-362. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.07
Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 363-376. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.08
Quarterly Journal of Engineering Geology and Hydrogeology November 01, 1974, Vol.7, 377-384. doi:https://doi.org/10.1144/GSL.QJEG.1974.007.04.09
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