Quaternary debris flows derived from ophiolite melange in northern Southland, New Zealand, are locally cemented and veined by cross-fiber and fine-grained chrysotile. Chrysotile was identified by optical, X-ray powder diffraction, electron microprobe, differential thermal (DTA), and infrared analysis methods. Microprobe and DTA also suggested the presence of as much as 6% of sub-microscopic, noncrystalline alumina, probably in the form of pseudoboehmite. Cavity fillings and irregular veins containing chrysotile are as thick as 40 cm and commonly contain lizardite clasts. Calcite commonly accompanies chrysotile as a vein mineral. Magnetite and pyrite are found near and adjacent to chrysotile veins. These accessory minerals imply that the chrysotile formed under alkaline, reducing conditions. Surface water seepages have pH = 9. Remnant debris-flow topography, Holocene radiocarbon dates, and the absence of hot spring activity confirms that chrysotile can form under near-surface, low-temperature conditions. Growth of chrysotile fibers on a lizardite substrate suggests that the chrysotile formed by solution of detrital lizardite and subsequent precipitation in cavities within the debris flow.

During Lateglacial cold periods, permafrost developed throughout Scotland, sediment-mantled slopes were extensively modified by solifluction and other forms of periglacial mass movement, large-scale sorted patterned ground formed on plateaux, and enhanced rockfall resulted in talus accumulation below cliffs. Most rock-slope failures occurred within five millennia following ice-sheet deglaciation, with many probably triggered by uplift-induced earthquakes; numerous debris-free scarps represent sites where Lateglacial rockslide debris was excavated by glaciers during the Younger Dryas Stade (∼12.9–11.7 ka). Sandar and outwash fans deposited by glacial rivers during ice-sheet retreat were incised to form high-level terraces. Under the cool temperate but relatively stable climate of the Holocene, solifluction and patterned ground formation continued to operate on high ground, though accumulation of high-level aeolian deposits on most mountains was terminated by erosion during the Little Ice Age. Drift-mantled slopes and talus slopes have been extensively eroded by translational failures and debris flows, the latter depositing debris cones on upland valley floors. The incidence of Holocene rockslides has been much lower than during the Lateglacial period. Dating of alluvial deposits and low Holocene terraces suggests no consistent pattern of Holocene floodplain evolution: incision has apparently dominated in the Highlands, aggradation in the lowlands, and floodplains in the Southern Uplands have asynchronous histories of incision and aggradation. Studies of floodplain behaviour over the past 200–300 years suggest that though major floods rework the floodplains of braided and piedmont rivers, there is no tendency towards net floodplain aggradation or incision. Most valley-side alluvial fans accumulated episodically in the last 4000 years, many in response to lowering of hillslope stability by woodland clearance. For many postglacial landsystems, disentangling the effects of declining paraglacial sediment supply, climate change and local influences (extreme rainstorm events or anthropogenic impacts) remains challenging.

Carbonate boulders transported down steep tributary channels by debris flow came to rest on Holocene debris fans beside the Colorado River in Grand Canyon National Park. Weakly acidic rainfall and the metabolic activity of blue-green algae have produced roughly hemispheric dissolution pits as much as 2-cm deep on the initially smooth surfaces of the boulders. The average depth of dissolution pits increases with relative age of fan surfaces. The deepening rate averages 2.4 mm/1000 yr (standard error = 0.2 mm/1000 yr), as calculated from several radiometrically dated surfaces and an archeological structure. This linear rate, which appears constant over at least the past 3000 yr, is consistent with field relations limiting the maximum age of the fans and with the physical chemistry of limestone dissolution. Dissolution-pit measurements ( n= 6973) were made on 617 boulders on 71 fan surfaces at the 26 largest debris fans in Grand Canyon. Among these fan surfaces, the average pit depth ranges from 1.2 to 17.4 mm, and the resulting pit dissolution ages range from 500 to 7300 cal yr B.P. Most (75%) surfaces are younger than 3000 yr, probably because of removal of older debris fans by the Colorado River. Many of the ages are close to 800, 1600, 2300, 3100, or 4300 cal yr B.P. If not the result of differential preservation of fan surfaces, this clustering implies periods of heightened debris-flow activity and increased precipitation.

Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat (Neotoma) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~ 10,700–9500, 7200–6700, 2400–2000, 850–700, and 550–400 cal yr BP, whereas ~ 9500–7200, 6700–4700 and ~ 1500–1000 cal yr BP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800 cal yr BP, respectively, though pinyon did not expand broadly until ~ 700 cal yr BP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~ 850–700 and 550–400 cal yr BP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon–juniper densification and cheatgrass invasion.

A Late Jurassic sauropod bone-bed comprising thousands of individual skeletal elements in the Morrison Formation of Montana, USA, is re-analysed to further elucidate its taphonomic history. New data gained from detailed contextual sampling is assembled and presented to test the hypothesis of a drought-induced, mass-mortality assemblage, and its subsequent depositional emplacement by a debris flow. Large dinosaur bone-beds are well-known in the Morrison, yet the Mother's Day Quarry site is unique for the formation in depicting an apparent debris flow deposit. Use of a computer program tailored to the data allows three-dimensional reconstruction of the bone-bed and recreates the palaeoslope of the deposit, adding support to the debris flow hypothesis. Such digital manipulation of field data may allow a deeper understanding of other bone-bed origination events.

Research on the British Paleocene Igneous Province (BPIP) has historically focused on the emplacement, chemistry and chronology of its elaborate central intrusive complexes and lava fields. However, the BPIP has also been dramatically shaped by numerous erosion, sedimentation and volcano-tectonic events, the significance of which becomes ever clearer as localities in the BPIP are re-investigated and our understanding of volcano-sedimentary processes advances. The resultant deposits provide important palaeo-environmental, palaeo-geographical and stratigraphical information, and highlight the wide range of processes and events that occur in ancient volcanic settings such as the BPIP. In this paper we review the sedimentary and volcano-tectonic processes that can be distinguished in the BPIP, and conceptualize them within a generalized framework model. We identify, and describe, the sedimentary responses to four broadly chronological stages in the history of the BPIP volcanoes: (1) the development of the lava fields, (2) early intrusion-induced uplift, (3) caldera collapse and (4) post-volcano denudation and exhumation of central complexes. We highlight and illustrate the range of sedimentary processes that were active in the BPIP. These operated on and helped shape a dynamic landscape of uplands and lowlands, of alluvial fans, braided rivers, lakes and swamps, and of volcanoes torn apart by catastrophic mass wasting events and/or caldera collapse.

The Southern Mountains Zone of the Rum Central Complex lies inside a major ring fault and comprises an intricate association of country-rock outcrops, breccias and rhyodacite. The breccias and rhyodacite were long thought to be products of subterranean explosion and intrusion, respectively. Here, we report new observations that support re-interpretation of these units as mass movement deposits and ignimbrites. The most abundant breccias (Coire Dubh-type) consist mainly of country-rock clasts <1 m in diameter in a sand or silt matrix. Internally bedded and graded, and interlayered with sandstones and lithic tuffs, these breccias are interpreted as debris flow and stream flow deposits. Rhyodacite sheets show gradational or sharp, concordant contacts with Coire Dubh-type breccias, and display graded basal lithic tuffs and graded fiamme swarms. These sheets are interpreted as moderately to densely welded rhyodacite ignimbrites (25–100 m thick). A steep body of fragmented (fiamme-bearing) rhyodacite with intrusive non-fragmented contacts is interpreted as an ignimbrite vent system. The rhyodacite and breccia succession is over 200 m thick and unconformably overlies a structurally uplifted Precambrian basement, within which there is also evidence of later subsidence. Outcrops of potential caldera-collapse ‘megabreccia’ are more structurally consistent than previously thought, and are re-interpreted here as coherent segments of Precambrian country rock (caldera floor). The Southern Mountains Zone breccias and rhyodacites respectively reflect sedimentary and pyroclastic processes acting in response to a complex tectonic interplay of intrusion-related uplift and caldera subsidence.