The quaternary stratigraphy of mount Etna,sicily: the effects of differing palaeoenvironments on styles of volcanism

Using recently published radiometric dates of important horizons within the Etna succession, correlations are proposed with the Late Quaternary biostratigraphies of the Italian mainland and the Mediterranean sea floor. This enables palaeoclimatic, palaeohydrological and palaeogeographical conditions on Etna to be established at stages in the volcano's evolution. It is argued that several major volcaniclastic suites were formed through the operation of processes that were under complex environmental, rather than simple volcanological control alone. In particular it is suggested that certain episodes of phreatomagmatic and laharic activity cannot be related to episodes of more evolved magma production, but rather to times during which the environment, height and configuration of Etna favoured the eruption and emplacement of these deposits. The authors reiterate their explanation of the formation of the Valle del Bove through processes of massive slope failure and indicate that conditions favouring this occurred at an appropriate stage in the history of the volcano. It is concluded that on active basaltic volcanoes, especially those like Etna which are also high mountains, the explanation of more violent phases requires the consideration of both internal volcanological and external environmental and morphological variables and that this is particularly important when its development has been set within the context of Late Quaternary environmental change. Finally the implications of these findings for the assessment of hazard are considered.

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Resumé Utilisant récemment des publications sur les datations radiométriques de couches importantes à l'intérieur de la succession de l'Etna, nous proposons d'établir des corrélations entre les biostratigraphies du Quaternaire Récent de la Péninsule Italienne et due fond marin Méditerranéen. Par ce procédé, nous pouvons établir les conditions paléoclimatiques, paléohydrologiques et paléogéographiques par stades selon l'évolution du volcan, capendant il faut tenir compte du fait que plusieurs suites volcaniclastiques majeures se sont formées à partir d'opérations de processus qui etaient eux-mêmes sous une complexe influence écologique plutôt que volcanologique seulement. Il est suggéré, en particulier, que certains épisodes d'activités phreatomagmatiquer et laharique ne puissent être reliés à des épisodes de production de magma plus elaborée, mais plutôt à des périodes pendant lesquelles le milieu, la hauteur et la configuration de l'Etna ont favorisé l'éruption et la localisation de ces dépôts. Les auteurs réitèrant leur explication sur la formation de la Vallée del Bove selon un processus de rupture radicale de pente et indiquent que les conditions favorables à ce dernier sont survenues à un stade opportun dans l'histoire du volcan. Ceci amènè à conclure que, sur des volcans basaltiques actifs comme l'Etna en particulier qui sont egalement des montagnes élevées, l'explication de phases plus violentes demande la consideration de facteurs volcanologiques internes d'une part, et morphologiques et écologiques externes d'autre part et que ceci est essential lorsque son développement a été fixé dans le contexte du changement de milieu au Quaternaire Recent. Enfin, il faut tenir compte de l'implication de ces résultats face aux incidences de risques.

     

Atrazine Used as a Tracer of Induced Recharge

The city of Lincoln draws water from a well field along the banks of the Platte River in east-central Nebraska. We have been able to follow the infusion of atrazine into this well field under induced recharge. Samples of water from the river, several monitoring wells and a production well were analyzed by GC/MS and solid phase extraction and found to change in concentration over the range 0.1 and 5.0 ppb of atrazine through the spring, summer, and fall 1989. Increases in the concentration of atrazine relating to precipitation events in the Platte River Basin were observable in the well water samples and ultimately in Lincoln municipal tap water. Atrazine from the river was seen to move via induced recharge and into well field ground water and away from the river at an observable rate. The concentration of atrazine in the river is dependent upon time of year and precipitation in the river basin.     

Glacial–interglacial sediment transport to the Meiji Drift,northwest Pacific Ocean: Evidence for timing of Beringian outwashing

A large sediment deposit known as the Meiji Drift, located in the northwestern Pacific Ocean, is thought to have formed from deep water exiting the Bering Sea, although no notable deep water forms there presently. We determine the terrigenous sources since 140 ka to the drift using bulk sediment ⁴⁰Ar–³⁹Ar and Nd isotopic analyses on the silt-sized (20–63 μm) terrigenous fraction from Ocean Drilling Program (ODP) Site 884 to reconstruct paleo-circulation patterns. There are large changes in both isotopic tracers, varying on glacial–interglacial cycles. During glacial intervals, bulk sediment ⁴⁰Ar–³⁹Ar ages range between 40 and 80 Ma, while Nd isotopic values range from ε_Nd = ? 1 to + 2. During interglacial intervals, sediments become much younger and more radiogenic, with bulk sediment ages falling to 2–15 Ma and Nd isotopic values ranging between ε_Nd = + 5 and + 9. These data and quantitative comparison to potential source rocks indicate that the young Kamchatkan and Aleutian Arcs, lying NW and NE of the Meiji Drift, contribute the majority of sediment during interglacials. Conversely, older source rocks, such as those drained by the Yukon River and northeast Russia are the dominant origin of sediments during glacials. Mixing model calculations suggest that as much as 35–45% of the sediment deposited in the Meiji Drift during glacials is from the Bering Sea. It remains unclear whether thermohaline-type circulation or focussing of Bering Sea flow lead to the glacial–interglacial sediment source changes observed here.     

Post-collapse volcanic history of calderas on a composite volcano: an example from Roccamonfina,southern Italy

Roccamonfina, part of the Roman Potassic Volcanic Province, is an example of a composite volcano with a complex history of caldera development. The main caldera truncates a cone constructed predominantly of this caldera may have been associated with one of the ignimbritic eruptions of the Brown Leucitic Tuff (BLT) around 385 000 yr BP. The Campagnola Tuff, the youngest ignimbrite of the BLT, however, drapes the caldera margin and must postdate at least the initial stages of collapse. During the subsequent history of the caldera there were several major explosive eruptions. The largest of these was that of the Galluccio Tuff at about 300 000 yr BP. It is likely that there was further collapse within the main caldera associated with these eruptions. It is of note that despite these subsequent major explosive eruptions later collapse occurred within the confines of the main caldera. Between eruptions caldera lakes developed producing numerous lacustrine beds within the caldera fill. Extensive phases of phreatomagmatic activity generated thick sequences of pyroclastic surge and fall deposits. Activity within the main caldera ended with the growth of a large complex of basaltic trachyandestite lava domes around 150 000 yr BP. Early in the history of Roccamonfina sector collapse on the northern flank of the volcano formed the northern caldera. One of the youngest major events on Roccamonfina occurred at the head of this northern caldera with explosive activity producing the Conca Ignimbrite and associated caldera. There is no evidence that there was any linkage in the plumbing systems that fed eruptions in the main and northern calderas.     

Mascali,Mount Etna Region Sicily: An Example of Fascist Planning During the 1928 Eruption and Its Continuing Legacy

The 1928 eruption of Etna, Sicily, although the largest such event this century, has not been studied in detail. In this paper the nature of the eruption, the destruction it caused – including the complete devastation of the town of Mascali (pre-eruption population 2,000) – and emergency responses of the authorities to it are reviewed in the context of fascist politics and planning priorities. It is contended that, although at one level the response to the 1928 eruption was successful, at another fascism merely continued and enhanced a reactive, propitiatory approach to hazard mitigation. We argue that this legacy was not successfully overcome until the middle of the nineteen eighties. Finally contemporary Italian moves towards a more proactive approach to disaster planning, both generally and in the context of Etna, are discussed.     

Caldera morphology in the western Galápagos and implications for volcano eruptive behavior and mechanisms of caldera formation

Caldera morphology on the six historically active shield volcanoes that comprise Isabela and Fernandina islands, the two westernmost islands in the Galapagos archipelago, is linked to the dynamics of magma supply to, and withdrawal from, the magma chamber beneath each volcano. Caldera size (e.g., volumes 2–9 times that of the caldera of Kilauea, Hawai'i), the absence of well-developed rift zones and the inability to sustain prolonged low-volumetric-flow-rate flank eruptions suggest that magma storage occurs predominantly within centrally located chambers (at the expense of storage within the flanks). The calderas play an important role in the formation of distinctive arcuate fissures in the central part of the volcano: repeated inward collapse of the caldera walls along with floor subsidence provide mechanisms for sustaining radially oriented least-compressive stresses that favor the formation of arcuate fissures within 1–2 km outboard of the caldera rim. Variations in caldera shape, depth-to-diameter ratio, intra-caldera bench location and the extent of talus slope development provide insight into the most recent events of caldera modification, which may be modulated by the episodic supply of magma to each volcano. A lack of correlation between the volume of the single historical collapse event and its associated volume of erupted lava precludes a model of caldera formation linked directly to magma withdrawal. Rather, caldera collapse is probably the result of accumulated loss from the central storage system without sufficient recharge and (as has been suggested for Kilauea) may be aided by the downward drag of dense cumulates and intrusives.