Base surge deposits in pleistocene volcanic ash near Rome

Mattson, Peter H.; Álvarez, Walter

doi:10.1007/bf02596891

Cited by 25 publications

(15 citation statements)

References 14 publications

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“…9-25). Most range from about 0.3 m to 7 m across and are a few centimeters to 3 m deep, but unusually large channels (30 m broad, 20 m deep) are reported by Losacco and Parea (1969), Mattson and Alvarez (1973) and Heiken (1971) and occur at Laacher See, Eifel, Germany ( Fig. 9-25).…”

Section: U-shaped Channelsmentioning

confidence: 75%

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Pyroclastic Rocks

Fisher¹,

Schmincke²

1984

1,223

590

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Section: U-shaped Channelsmentioning

confidence: 75%

“…U-shaped channels in base surge deposits, described by several authors (Losacc<,> and Parea, 1969;Fisher and Waters, 1970;Mattson and Alvarez, 1973;Heiken, 1971;Schmincke, 1977b;Fisher, 1977;Nairn, 1979), are symmetrical in cross section, with curving bottoms that clearly cut underlying layers ( Fig. 9-25).…”

Section: U-shaped Channelsmentioning

confidence: 85%

Pyroclastic Rocks

Fisher¹,

Schmincke²

1984

1,223

590

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“…Schmincke et al ., ; Cole, ; Douillet et al ., , and references therein). Early authors have suggested that these characteristics could link to the interpretation as Froude‐supercritical bedforms (Fisher & Waters, , ; Waters & Fisher, ; Crowe & Fisher, ; Mattson & Alvarez, ; Schmincke et al ., ). Subsequently, this stoss‐aggrading characteristic of the deposits has largely been taken as a straightforward argument for parental Froude‐supercritical flows without further debate (Fisher, ; Yokoyama & Tokunaga, ; Wohletz & Sheridan, ; Walker et al ., ; Fisher et al ., ; Suthren, ; Charland & Lajoie, ; Sohn & Chough, ; Giannetti & Luongo, ; Brand & White, ; Gençalioğlu‐Kuşcu et al ., ; Brand & Clarke, , ; Brand et al ., ; Kelfoun et al ., ).…”

Section: Introductionmentioning

confidence: 99%

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

et al. 2018

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Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid-turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss-face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive-based backset beds are evidenced. Recurrent trains of subvertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse-grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow-perpendicular and flow-parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope-influenced saltation; (iii) truncative bursts; and (iv) granular-based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude-supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and 'chute and pools' can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible 1531 role of coherent flow structures such as G€ ortler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre-existing morphology. Quantification of near-bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0Á30 m.s À1 (equivalent to pure wind velocity of 6 to 8 m.s À1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s À1 .

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“…Moore, 1967;Waters & Fisher, 1971;Kienle et al, 1980; and studies of well-exposed Cainozoic base-surge successions (e.g. Fisher & Waters, 1970;Crowe & Fisher, 1973;Mattson & Alvarez, 1973;Schmincke et al, 1973;Yokoyama & Tokunaga, 1978;Wohletz & Sheridan, 1983;Sohn & Chough, 1989, 1992, indicate that base-surge deposits are almost entirely restricted to constructional ramparts of phreatomagmatic ejecta, termed maars, tuff rings or tuff cones, which¯ank the source volcanic vent. Although most studied examples are from basaltic volcanic centres, base-surge deposits have also been Sedimentology (2000) 47, 87±98 Ó 2000 International Association of Sedimentologists described from intermediate and silicic volcanic centres (e.g.…”

Section: Introductionmentioning

confidence: 99%

Distinguishing base‐surge deposits and volcaniclastic fluviatile sediments: an ancient example from the Lower Devonian Snowy River Volcanics, south‐eastern Australia

Bull

2000

Sedimentology

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A 500‐m‐long road cutting in the Lower Devonian Snowy River Volcanics (SRV), eastern Victoria, Australia, exposes phreatomagmatic units and volcaniclastic sediments. Based on bed geometry, sorting and sedimentary structures, it was possible to distinguish base‐surge deposits from ephemeral fluvial deposits in this relatively well‐exposed ancient succession. Where the base‐surge deposits infill irregular topography, bed sets mantle the pre‐existing surface but thicken into topographic lows. In contrast, where the fluvial deposits infill topographic depressions, beds onlap laterally against channel walls. In addition, curvi‐planar slide surfaces within the base‐surge deposits generated by inter‐eruptive slumping indicate rapid emplacement as a constructional tuff rampart (? maar). The base‐surge deposits are always poorly sorted and commonly contain accretionary lapilli, reflecting their deposition from turbulent, low‐particle‐concentration, steam‐rich pyroclastic currents. In contrast, the fluvial deposits are relatively well‐sorted, reflecting hydraulic sorting and winnowing during tractional transport and deposition. There are significant differences in the types of sedimentary structures present. (1) Bedding in the base‐surge deposits is entirely tabular, and beds can be traced laterally to the limits of the outcrop. In contrast, the fluvial deposits have abundant internal scour surfaces that result in beds/bedding intervals lensing out laterally over intervals of the order of 5–10 m. (2) Cross‐beds with relatively high‐angle foresets are restricted to the fluvial deposits. (3) Laterally persistent tabular beds that contain abundant, densely packed accretionary lapilli are restricted to the base‐surge deposits. In summary, although base‐surge deposits and ephemeral fluvial deposits can appear superficially similar, it is possible to apply facies models carefully to distinguish between them, even in ancient successions.

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Base surge deposits in pleistocene volcanic ash near Rome

Cited by 25 publications

References 14 publications

Pyroclastic Rocks

Pyroclastic Rocks

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Distinguishing base‐surge deposits and volcaniclastic fluviatile sediments: an ancient example from the Lower Devonian Snowy River Volcanics, south‐eastern Australia

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