ABSTRACT This field trip highlights evidence of late Pliocene–early Pleistocene submarine and subaerial volcanism coeval with marine and marginal-marine sedimentation in the Santa Rosalía Basin in Baja California. The best exposures of these rocks occur at the El Álamo Canyon, which exhibits outcrops of the Tirabuzón and Infierno formations interbedded with submarine and subaerial volcanic and volcaniclastic deposits that are covered by the subaerial ignimbrites of Reforma and Aguajito calderas. Extensive field mapping and stratigraphy carried out in this canyon, aided with 40 Ar/ 39 Ar, and U-Pb geochronology, allowed us to divide the stratigraphy into three main sequences that, from base to top, are: (1) Santa Rosalía succession, (2) the Reforma caldera complex, and (3) El Aguajito caldera. This refined stratigraphy indicates that eight episodes of volcanism occurred between 2.5 and 1.36 Ma, during marine sedimentation in an internal continental shelf and in estuaries, coastal lagoons, or protected bays as supported by the fossil record. This sedimentary and volcanic interbedding suggests transgressions and regressions of the sea level, as well as tectonic uplifting. After the inception of volcanism in the Reforma caldera complex (1.29 Ma), the area emerged from these shallow seas followed by the formation of the Aguajito caldera (1.1 Ma), and then later on by the Tres Vírgenes volcanic complex (0.3 Ma). The last complex erupted a lava flow ca. 22 ka that so far stands as the youngest activity in the region. The magmatic evolution in the region is characterized by post-subduction calc-alkaline magmatism. Such magmatism is expressed as pure calc-alkaline rocks from El Aguajito–Reforma calderas, and as hybrid transitional magmas formed by adakitic rocks from the Tres Vírgenes volcanic complex.

Abstract The temperature of the deposits ( T dep ) emplaced by the pyroclastic density current (PDC) generated by the seven major explosive eruptions from Somma–Vesuvius during the last 22 kyr were investigated using the thermal remanent magnetization (TRM) of lithic clasts embedded within the deposits. New data are presented for the Pomici di Base, Greenish Pumice, Mercato and 1631 AD deposits and compared to the literature data from the Avellino, 79 AD-Pompeii and 472 AD-Pollena eruptions. The T dep mainly fall in the range 270–370 °C and no significant correlation is evidenced between sedimentological features, eruptive and depositional processes and the final T dep . The admixture of ambient air during the run-out appears the most effective process to cool the temperature of the ash and gases of the PDC, and is therefore the main factor affecting the deposit temperature.

Abstract New data on the pyroclastic density current (PDC) deposit temperature ( T dep ) are provided for two prominent eruptions of Mexican volcanoes of the twentieth century: the 1982 eruption of El Chichón and the 1913 eruption of Colima. In spite of similar lithofacies, magma composition and pre-eruptive conditions, the T dep of the PDCs from the 1982 (El Chichón) and 1913 (Colima) eruptions differ significantly, with intervals of T dep of 360–420 °C and 250–330 °C, respectively. These new data emphasize that a full understanding of the physical mechanisms responsible for equilibrium temperature attainment within a pyroclastic deposit has not yet been realized. The T dep measured for El Chichón PDC deposits confirm the preliminary data published elsewhere, while Colima magnetic temperatures provide different values to those published previously. Supplementary material: T dep measurements for the different sites at El Chichon volcano and Colima volcano are available at: http://www.geolsoc.org.uk/SUP18695 .

Volcaniclastic debris flows generated in drainage basins of the Apennine mountains of southern Campania in response to pyroclastic fall deposition from four Holocene eruptions of Somma-Vesuvius: Avellino (3.8 ka), A.D. 79, A.D. 472, and A.D. 1631. These syneruptive debris flows are lithologically homogeneous and contain more than 90% of material from the parental eruption. They differ from inter-eruptive debris flows recognized in the area, which contain mixed lithologies of juvenile material (i.e., volcanic material from different eruptions). Diffuse rill erosion generated fines-rich volcaniclastic flows (mudflows), whereas partial saturation of coarse ash and lapilli generated coarser-grained debris flows. Lithofacies analysis shows that debris flows predominate versus hyperconcentrated flows and normal stream-flow deposits. Debris-flow deposits are massive, matrix supported, and have a gravelly-sandy texture. Large blocks are scarce due to their absence in the pyroclastic source material. Lithofacies association indicates that volcaniclastic debris-flow deposits aggraded rapidly by superimposition of different surges that spontaneously developed within the flow. Bulk-flow density ranges from 1840 to 2260 kg/m 3 (mean 2035 ± 207 kg/m 3 ). Geological data supported some considerations of hazard assessment in the study area and indicate that the syneruptive volcaniclastic flows stopped distally on active alluvial fans.

Abstract During the Bronze Age, Vesuvius had a Plinian eruption whose deposits are known as the Avellino Pumice. The eruption spread a blanket of white and grey pumice across southern Italy, and there was a severe impact on proximal areas. Assessment of volcanological factors for the Plinian phase gives intensities of 5.7 × 10 7 kg s -1 for the white pumice phase and 1.7 × 10 8 kg s -1 for the grey pumice phase, corresponding to column heights of 23 and 31 km, respectively. Volume (magnitude) calculations using the crystal concentration method (CCM) give respectively 0.32 and 1.25 km 3 of deposit, in a total minimum period of about 3 h. Archaeometric studies on Bronze Age domestic pottery from several settlements in Apulia (SE Italy) reveal the presence of pumice fragments mixed with the clay, and petrological and chemical criteria suggest that these pumices are from the Avellino eruption. This relationship allows us to fix precise correlations between different archaeological facies of the Italian Bronze Age. To explore the possibility of an extensive use of pumices in these distal regions (about 140 km from Vesuvius), we calculated the possible thickness of the tephra blanket. We propose a method to extrapolate proximal data on the deposit to calculate its minimum distal thickness. Such a method could also be used in volcanic hazard studies to assess the distal impact of large past eruptions.