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The occurrence of pyroclastic flow deposits is not restricted to polygenetic and/or felsic volcanic systems, but can also occur at mafic monogenetic volcanic centres. At the c. 5 ka Mt Gambier Volcanic Complex, Australia, two small-volume pyroclastic flow deposits resulted from phreatomagmatic eruptive phases of the Blue Lake East and the Valley Lake maar craters. The facies descriptions of the two massive, poorly sorted lapilli tuff and tuff breccia deposits are given. Low-grade carbonized wood fragments in the deposits mark low emplacement temperatures (180–270°C) for these deposits with only c. 12–23% of the total thermal energy of the original magma preserved at the time of deposition. The Blue Lake East vent erupted by forming a short-lived vertical eruption column, which could not be sustained and collapsed. The Valley Lake pyroclastic flow deposit has a highly asymmetric dispersal to the west, indicating that this deposit was formed during an eruptive phase with a large westward-directed lateral component. Such massive, poorly sorted deposits outside the maar crater indicate that some similar deposits in diatremes may have originated from surface eruptions and not just from subsurface debris jets.

The Sgurr of Eigg Pitchstone on the Isle of Eigg, NW Scotland, is a crystal-rich, trachydacitic, partially vitrophyric rock, which has previously been interpreted both as a lava and as a sill. We interpret this rock as a chemically zoned, rheomorphic, lava-like ignimbrite that formed during a sustained pyroclastic eruption. The Sgurr of Eigg Pitchstone can be subdivided into discrete emplacement units distinguished by the following features: (1) their present-day weathering characteristics; (2) the orientation, spacing and morphology of the columnar joints; (3) sharp, undulating boundaries with marked topographic breaks. The absence of weathered surfaces, palaeosols, pyroclastic fall deposits or sedimentary rocks at emplacement unit boundaries suggests deposition from a single eruption. The emplacement units, some of which display upper and basal vitrophyres, represent distinct depositional packages that record several rapidly emplaced ignimbrites, which welded, cooled and devitrified as a simple, essentially single, cooling unit, during eruption from a sustained, low pyroclastic column. The Sgurr of Eigg Pitchstone displays a pervasive base-parallel flow banding, which is folded into intrafolial recumbent isoclinal folds. The flow banding and folds indicate that rheomorphism occurred throughout deposition. The Sgurr of Eigg Pitchstone is interpreted as an erosional remnant of an extensive ignimbrite sheet, the first such unit recorded within the North Atlantic Igneous Province.

The ad 79 Plinian eruption of Vesuvius that buried Pompeii and Herculaneum began with pumice falls deposited towards the SE of the volcano followed by pyroclastic currents directed towards the SW. These currents reached Herculaneum and rapidly entered the sea, forming a fan. The interpretation of seismic reflection profiles and gravity cores collected off Herculaneum documents a submarine fan-shaped pyroclastic body at 10–140 m water depth that we interpret as the submarine counterpart of the onshore pyroclastic current deposits. This fan, c . 0.3 km 3 in volume, displays a chaotic seismic facies that changes seaward to parallel reflectors and then to wavy reflectors. Gravity cores reveal a succession consisting of centimetre-thick sand- or silt-sized ash couplets followed by a graded gravelly sand-sized bed up to 180 cm thick, containing shell fragments and beach-derived pebbles, overlain by centimetre-thick graded and laminated sandy ash layers. The depositional textures and sedimentary structures of the submarine pyroclastic fan have been interpreted as the product of the interactions between pyroclasts, water waves and tsunamis induced by the ad 79 pyroclastic density currents into the Bay of Naples.

Primary basaltic pyroclastic deposits compose volumetrically c . 35–50% of the Lower Palaeogene Vandfaldsdalen, Mikis and Haengefjeldet Formations within the lower volcanic series of the East Greenland flood basalt province. The eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break-up and initiation of flood basalt volcanism. We present a revised stratigraphy for the pre-volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the Kangerlussuaq Basin, East Greenland. Primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds, surge deposits and vent sites with cinder cones. Early volcanism was apparently restricted to localized basins and formed shield volcano structures 30–40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites, sediments, pyroclastic deposits and lavas. The lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the NE, paired with continued down-dropping of inactive volcanic centres. The complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting.

We have used a digital model of the topography of Montserrat, a simple mathematical model of gravitational flow and some assumptions of the way in which the next eruption will develop to create a map of the volcanic hazards from Soufriere Hills Volcano. This has been done using an image processing computer to simulate the deposits produced by pyroclastic flows. This technique has the advantages over more traditional cartographic methods of spatial precision, rapid computation of multiple eruption models and the explicit nature of the physical model used. Soufriere Hills Volcano is a small andesitic volcano characterized by a cluster of summit domes and an apron of pyroclastic flow deposits and mudflows upon which several thousand people now live. Most of the flanks were covered by deposits from a series of eruptions from 24000 to 16000 a BP, though there is some evidence that dome growth and small pyroclastic flows have occurred since. The modelling is constrained by field evidence from the deposits of previous eruptions. Although the evidence is not good enough to model individual flow units, the cumulative deposits can be used. From the eruption deposit models we have created a new type of map specifically for emergency planning. This sequential hazard zone map attempts to portray the regions that would be at hazard from pyroclastic flows during successive stages from the start of an eruption whose energy release was increasing with time.

New radiocarbon dates reveal that unlithified pyroclastic deposits erupted from Mt Misery, St. Kitts (principally the Mansion ‘Series’) range from older than 42 000 years to younger than 1750 years B.P. Previously published accounts of Mt. Misery have only described air-fall deposits. However, a newly recognized sequence of pyroclastic flow deposits within the Mansion ‘Series’ is dated as 2000 to 3000 years B.P. The presence of these young deposits indicates that Mt Misery,. like other Lesser Antillean volcanoes, also has a potential pyroclastic flow volcanic hazard.

The Minoan eruption of Santorini produced the following sequence of deposits: a plinian pumice fall deposit, interbedded surtseyan-type ash fall and base surge deposits, mud-flow deposits and ignimbrite interbedded with very coarse, well-sorted flood deposits. The variation of thickness and grain size in the plinian deposit indicates a vent 1 km west of Thera town. The base surges and surtseyan-type activity is interpreted as the result of sea water entering the magma chamber. The poorly sorted mud-flow deposits and ignimbrite are distinguished on their grain size, temperature and morphological characteristics, which indicate substantial rheo-logical contrasts in the mass flows which produced them. Grain size analyses show wide ranges in the lithic contents of the different types of deposit: ignimbrite (35–60%), mud-flows (20–30%) and the pyroclastic fall and base surge deposits (4–15%). The ignimbrite is enriched in crystals, complemented by depletion in fine air-fall ash beds that interstratify with the ignimbrite. The gas velocity of the plinian phase is estimated as 550 m/s, the eruption column height as greater than 20 km and it is shown that only particles of 2 mm could have reached Minoan Crete.

Thick accumulations of pyroclastic deposits have emanated from the Mt Misery volcano on St Kitts, Lesser Antilles, during two major eruptive episodes (2-3000 and 41000 a BP). Systematic logging of coastal sections in the northern part of the island has revealed a variety of deposits, including pyroclastic flows, surges and intermittent air fall. Palaeosols and one laterally persistant surge deposit provide important marker horizons, permitting correlation of the intervening and less persistent flow deposits. Block and ash flows (traditionally termed nuee ardentes) can be subdivided into andesitic Pelean-type and basaltic andesite St Vincent-type deposits, closely corresponding to the products of historic pyroclastic eruptions in the Lesser Antilles. Finer grained ash flows are equally voluminous and comprise scoria, semi-vesicular andesite and mixed magma and ash deposits. A significant pyroclastic surge component has been recognized with characteristic bedforms. Field evidence suggests that there is a continuous gradation between flow and surge deposits. Collectively the pyroclastic flow deposits are all of the small volume type and are commonly stratified, with poor to moderate sorting and coarse tail grading. Where thickly developed they show an internal depositional sequence compatible with the standard ignimbrite flow unit. Well developed bedforms include steeply incised U-shaped gullies eroded by the infilling flows. The depositional characteristics of these pyroclastic flows appears to be a function of the physical properties of the magma on eruption, initial flow magnitude, potential energy and degree of topographic channel formation. In general grain-size and the erosive potential of the flow increases with increasing channel formation, whilst sorting and the degree of stratification decrease. The development of graded bedding is, however, apparently unaffected.

Vulcanian explosions generate some of the most hazardous types of volcanic phenomena, including pyroclastic density currents. Non-vertical directionality of an explosion promotes asymmetrical distribution of proximal hazards around the volcano. Although critical, such behaviour is relatively uncommon and has been seldom documented. Here we present, for the first time, evidence both from geophysical monitoring and field survey data that records the occurrence of such an event. Thermal imagery captures a Vulcanian explosion at Soufriere Hills Volcano, Montserrat, which occurred during a large partial lava dome collapse in February 2010, and was inclined at about 25° from the vertical in a northerly direction. Pyroclastic products were preferentially distributed to the north and included: an unusual pumice boulder deposit that we propose was formed by a dilute pyroclastic density current; pumice flow deposits; and a proximal lapilli and block fallout lobe. The inclined nature of the explosion is attributed to the asymmetric geometry around the vent. The explosion-derived pyroclastic density currents had notably lower velocities than those associated with lateral blasts, which, we suggest, result from a separate and distinct mechanism. These inclined explosions present an additional mechanism that is able to generate directed pyroclastic density currents, with consequent implications for hazard assessment.