Abstract Central Skåne (Scania) in southern Sweden hosts evidence of extensive Jurassic volcanism in the form of mafic volcanic plugs and associated volcaniclastic deposits that entomb well-preserved macro-plant and spore–pollen assemblages. Palynological assemblages recovered from the Höör Sandstone are of Hettangian–Pliensbachian age and those from the overlying lahar deposits are dated as Pliensbachian–early Toarcian (?). Palynomorph assemblages from these units reveal significantly different ecosystems, particularly with respect to the gymnospermous components that represented the main canopy plants. Both palynofloras are dominated by osmundacean, marattiacean and cyatheacean fern spore taxa but, whereas the Höör Sandstone hosts abundant Chasmatosporites spp. pollen produced by plants related to cycadophytes, the volcanogenic deposits are dominated by cypress family pollen ( Perinopollenites ) with an understorey component rich in putative Erdtmanithecales (or possibly Gnetales), and collectively representing vegetation of disturbed habitats. Permineralized conifer wood attributed to Protophyllocladoxylon sp., belonging to plants that probably produced the abundant Perinopollenites grains, is abundant in the volcanigenic strata, and shows sporadic intraseasonal and multi-year episodes of growth disruption. Together with the relatively narrow but marked annual growth rings, and the annual and mean sensitivity values that span the complacent–sensitive domains, these features suggest growth within Mediterranean-type biomes subject to episodic disturbance.

Abstract The Middle Fork Nooksack River drains the southwestern slopes of the active Mount Baker stratovolcano in northwest Washington State. The river enters Bellingham Bay at a growing delta 98 km to the west. Various types of debris flows have descended the river, generated by volcano collapse or eruption (lahars), glacial outburst floods, and moraine landslides. Initial deposition of sediment during debris flows occurs on the order of minutes to a few hours. Long-lasting, down-valley transport of sediment, all the way to the delta, occurs over a period of decades, and affects fish habitat, flood risk, gravel mining, and drinking water. Holocene lahars and large debris flows (>10 6 m 3 ) have left recognizable deposits in the Middle Fork Nooksack valley. A debris flow in 2013 resulting from a landslide in a Little Ice Age moraine had an estimated volume of 100,000 m 3 , yet affected turbidity for the entire length of the river, and produced a slug of sediment that is currently being reworked and remobilized in the river system. Deposits of smaller-volume debris flows, deposited as terraces in the upper valley, may be entirely eroded within a few years. Consequently, the geologic record of small debris flows such as those that occurred in 2013 is probably very fragmentary. Small debris flows may still have significant impacts on hydrology, biology, and human uses of rivers downstream. Impacts include the addition of waves of fine sediment to stream loads, scouring or burying salmon-spawning gravels, forcing unplanned and sudden closure of municipal water intakes, damaging or destroying trail crossings, extending river deltas into estuaries, and adding to silting of harbors near river mouths.

Concepción is currently the most active composite volcano in Nicaragua. Ash explosions of small to moderate size (volcano explosivity index 1–2) have occurred on a regular basis. Gravity data collected on and around the volcano between 2007 and 2010 confirm that a younger cone is built atop an older truncated edifice of denser material, predominantly lavas. The bulk density of the volcanic cone is 1764 kg m −3 (with an uncertainty of at least ±111 kg m −3 ), derived from gravity data. This estimated bulk density is significantly lower than densities (e.g., 2500 kg m −3 ) used in previous models of gravitational spreading of this volcano and suggests that the gravitational load of the edifice may be much lower than previously thought. The gravity data also revealed the existence of a possible northwest-southeast–oriented normal fault (parallel to the subduction zone). Episodic geodetic data gathered with dual-frequency global positioning system (GPS) instruments at five sites located around the volcano's base show no significant change in baseline length during 8 yr and 2 yr of observations along separate baselines. Structures deformed after the Tierra Blanca Plinian eruption ca. 19 ka, which significantly altered the form and bulk density of the volcano, may be due to the spreading of the volcano, but may also be related to volcano loading, magmatic intrusions and their subsequent evolution, and other volcano-tectonic processes, or a combination of any of these factors. A joint interpretation of our gravity and geodetic GPS data of Concepción suggests that this volcano is not spreading in a continuous fashion; if it is episodically spreading, it is driven by magma intrusion rather than gravity. These results have important implications for volcanic hazards associated with Concepción Volcano. Although during the last 15 yr tephra fallout and volcanic debris flows (lahars) have been the pervasive hazards at this volcano, earthquakes from an eventual slip of the fault on the east-northeast side of the volcano (delineated from our gravity measurements) should be considered as another important hazard, which may severely damage the infrastructures in the island, and conceivably trigger a volcano flank collapse.

Hudson Volcano is one of the most active volcanoes in the southernmost Southern Andean volcanic zone, characterized by an ice-filled caldera 10 km in diameter. Tephrochronological studies indicate records of explosive activity from the late Pleistocene to historical times. In fact, the last large eruption occurred in August 1991 and is considered to be one of the largest eruptions of the twentieth century. The volcano is located in a remote and roadless region of the Patagonian Andes, which means that numerical models play an important role in assessing volcanic hazards at Hudson. In particular, these models are used to identify areas susceptible to be impacted by lahar flows and tephra fallout. In addition, a proximal-hazard zone was built using the energy cone model, which is useful when little or no prior geologic data are available. Lahar-inundation hazard zones were delineated using the LAHARZ model, based on empirical relationships. Several volumes were considered because of the range of potential lahar-initiating events, such as ice melting or mobilization of loose pyroclasts. Simulations indicate that valleys located west of the volcano are likely to be inundated by lahars, even small-volume lahars triggered by small eruptions, as have been recorded during historical episodes. In contrast, only large events would likely affect main populated settlements located farther west from the volcano. Tephra-fall deposits were simulated with an advection-diffusion model, Tephra2, employing wind data derived from atmospheric global data sets. Both spatial distribution of deposits and thickness derived from the August 1991 eruption were satisfactorily validated. Three eruptive scenarios were selected according to the geological record of the volcano. Results of simulations are outlined as probabilistic maps of mass accumulation on the surface and also as exceedance probability curves for selected localities. This analysis shows that regions east of the volcano are more vulnerable to tephra fallout throughout the year, and therefore no major interseasonal variability is recognized. However, the arrival of weather fronts, common during autumn and winter, could trigger tropospheric wind shifts, which may increase the chance of meridional (north-south) transport of pyroclasts. Finally, according to available tephrochronological data, the occurrence of a large eruption was estimated, indicating 10%–20% likelihood of an eruption ≥VEI 4 (where VEI is volcanic explosivity index) during the next 100 yr.

The field of volcanology has greatly changed during the last half century. The profession is now much more diverse and interdisciplinary, even including collaborating researchers from the social and medical sciences. This new mode of cooperation and working has been more successful in mitigating volcanic hazards and risks. There are fewer of the strong-willed lone rangers of the past and more of those who work with teams to more effectively understand how volcanoes work to protect those living on or near active or potentially active volcanoes. Moreover, there are more university departments with volcanology in their curricula and more international symposia and workshops focusing on mitigation of risk posed by volcano-related hazards. We all have respected colleagues and volcano observatories in many countries. The importance of understanding explosive volcanic eruptions and tracking of eruption plumes involves volcanologists, atmospheric physicists, and air-traffic controllers and is of great interest to the aviation industry. We now have the links in place between great science and practical applications.

Misti volcano in southern Peru has a record of explosive eruptions and a nearby population of over 810,000, making it a hazardous volcano. The city center of Arequipa, Peru's second most populous city, is 15 km from the summit of Misti, and many neighborhoods are closer. As the population increases yearly, the urban boundary continues to move up the south side of the volcano. Many parts of the city are built upon the deposits from Misti's most recent Plinian eruption at ca. 2 ka. The 2 ka Plinian eruption (Volcanic Explosivity Index [VEI] 5) produced a 1.4 km 3 tephra-fall deposit and 0.01 km 3 of pyroclastic-flow deposits in ~2–5 h. Column height varied during the eruption but ascended up to 29 km. Pyroclastic flows descended only the south side of the volcano. The tephra fall spread southwest, resulting in ~20 cm of tephra accumulation in the area now occupied by the city center. The flowage deposits were previously identified as pyroclastic-flow deposits, but new sedimentologic and textural evidence suggests that ~80% (by volume) of the deposits were emplaced wet and relatively cold. As such, they are lahar deposits. A Neoglacial advance concurrent with the eruption supports evidence for voluminous snow and ice on the edifice. Pyroclastic flows melted between 0.01 km 3 and 0.04 km 3 of ice and snow on the volcano, triggering lahars that descended the volcano and inundated channels and some interfluves on the south flank. The lahars evolved downstream from proximal debris flows to distal hyperconcentrated flows, emplacing ~0.04 km 3 of deposits. Four facies of lahar deposits are present in the channels and another facies occurs on the interfluves. Such a comprehensive understanding of the 2 ka eruption will help to inform future volcanic hazards assessments. Pyroclastic-flow and tephra-fall deposits of the same magnitude could occur again and are useful in hazards assessment. The 2 ka lahars required voluminous water, which is no longer available on the volcano, and, within modern climate conditions, these deposits are not representative of possible future events. Estimations of water available from modern rain and snow suggest that lahars with volumes between 1 × 10 5 m 3 and 3 × 10 6 m 3 are possible. Lahars are more likely if an eruption occurs during a period of high snow accumulation or during subsequent heavy rainfall. Lahars up to 1 × 10 7 m 3 are possible if the Río Chili is dammed during an eruption. Lahar hazard zones generated using these volumes suggest the largest lahars could enter Arequipa.