The volcanological significance of deep-sea ash layers associated with ignimbrites

Sparks, R. S. J.; Huang, T. C.

doi:10.1017/s0016756800028533

Cited by 83 publications

(56 citation statements)

References 22 publications

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“…The bimodal grain size distribution seen in CI deposits is also seen in deep sea deposits from the Minoan eruption of Santorini (Sparks & Huang 1980). Analysis of deep sea tephra from the Toba (75 ka) eruption shows a similar pattern to the very distal tephra seen here.…”

Section: Discussionsupporting

confidence: 74%

“…The tephra elutriated from pyroclastic density currents formed co-ignimbrite plumes rising 37 -40 km ) with grain size distributions much smaller and finer than those from the Plinian phase. At distances of 400-630 km from source, Sparks & Huang (1980) were able to identify Plinian deposits with a sharp upper contact separating them from an overlying co-ignimbrite deposit. At distances greater than 630 km, this contact becomes indistinct as the tephra from the two phases became mixed in the atmosphere.…”

Section: Discussionmentioning

confidence: 99%

“…Previous grain size analysis of deposits from deep sea cores was conducted by Sparks & Huang (1980) and Cornell et al (1983). Both studies sieved the coarse fraction of the deposits.…”

Section: The Campanian Ignimbrite (Ci) Eruptionmentioning

confidence: 99%

“…Both studies sieved the coarse fraction of the deposits. For the fine fraction, Cornell et al (1983) used a Particle Data electro-resistance size analyser, whereas Sparks & Huang (1980) used a Coulter counter. Both methods rely on the electrical resistivity of particles.…”

Section: The Campanian Ignimbrite (Ci) Eruptionmentioning

confidence: 99%

“…These studies noted a distinct bimodal character to deposits less than 800 km from source. Sparks & Huang (1980) commented that deposits at 440 and 630 km can be separated into a coarse lower unit dominated by elongate pumice separated by a sharp boundary from a fine-grained volcanic glass upper unit. Based on these physical differences the coarse pumice layer was attributed to the Plinian phase of the eruption and the fine-grained upper unit to the co-ignimbrite phase.…”

Section: The Campanian Ignimbrite (Ci) Eruptionmentioning

confidence: 99%

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Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption

Engwell

Sparks

Carey

2014

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Tephra deposits in the deep sea can survive undisturbed for long periods of time and, on regional scales, tend to be much better preserved than their subaerial counterparts. In this study, grain size distributions and thicknesses of tephra deposits from the Campanian Ignimbrite (CI) eruption (39 000 yr BP; magnitude c. 7.7) preserved in thirty-three deep sea cores are analysed to infer key eruption parameters. Distal deep sea tephra thickness data show an exponential decrease with distance from source. Such trends are difficult to identify in distal subaerial data owing to reworking and limited exposure. We find that tephra grain size distributions are much less affected by depositional environment than thickness, with trends that are consistent across distal subaerial, lacustrine and deep sea environments. The CI layer exhibits bimodal grain size distributions to distances of c. 1000 km, after which it becomes unimodal. Such trends can be related to different mechanisms of tephra transport in the atmosphere, whereby at proximal to medial distances the Plinian and co-ignimbrite phases produce distinct plumes. Within 150 and 900 km from source, Plinian tephra constitutes 40 + 5% of the deposit volume. Beyond this region where coarse particles are deposited, the plumes merge and fines derived largely from co-ignimbrite elutriation are spread in the atmosphere at velocities greater than the settling velocities of the particles.

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Section: Discussionsupporting

confidence: 74%

Section: Discussionmentioning

confidence: 99%

“…Previous grain size analysis of deposits from deep sea cores was conducted by Sparks & Huang (1980) and Cornell et al (1983). Both studies sieved the coarse fraction of the deposits.…”

Section: The Campanian Ignimbrite (Ci) Eruptionmentioning

confidence: 99%

Section: The Campanian Ignimbrite (Ci) Eruptionmentioning

confidence: 99%

Section: The Campanian Ignimbrite (Ci) Eruptionmentioning

confidence: 99%

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Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption

Engwell

Sparks

Carey

2014

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Impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 May 1980 Mount St. Helens fallout deposit

et al. 2015

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The 18 May 1980 eruption of Mount St. Helens started with a lateral blast that fed a pyroclastic surge, which then uplifted to form a co‐blast plume. Thirty minutes later, Plinian activity started at the vent and fluctuated in intensity for ~9 h. The resulting fallout deposit, documented to > 600 km from vent, presents some striking features: (1) displacement of the overall deposit to the north of the vent, (2) a secondary thickness and mass maximum at ~300 km from vent, (3) a total grain size distribution dominated by fine ash (62 wt % of the deposit < 63 µm), and (4) individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north. Results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of ∼15 µm. Relative proportions of each subpopulation vary asymmetrically in the crosswind directions, with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit, both reach their absolute maxima in mass on the deposit axis. Componentry analyses of selected samples show that blast‐derived material is greatly enriched toward the north of the deposit. These results indicate that the co‐blast plume dispersed fine‐grained material over great distances and dominated the fine subpopulation. Comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the (early) co‐blast plume and the (later) vent‐derived Plinian plumes. The co‐blast plume is displaced to the north; it had a high overshoot height, and eastward dispersion via strong winds low in the stratosphere (~10–15 km). The Plinian plumes were lower and dispersed most of the material to the southeast as the direction of high‐velocity winds shifted just before the late climactic Plinian eruptive phase. Fine ash (fine subpopulation) was deposited continuously throughout the deposit, with an increase of sedimentation rate ~300 km from the vent where there is a secondary maximum in the deposit mass and thickness. Fine ash probably settled by a combination of enhanced sedimentation mechanisms, including not only aggregation but also gravitational convective instabilities of cloud base, hydrometeor formation and destruction, and entrainment of small particles by larger ones. Finally, we show that half of the deposit (by mass) in the medial area was deposited by the co‐blast plume, and that a significant proportion of the Mount St. Helens fallout deposit is nonjuvenile, which has implications for the magmatic budget of this eruption.

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Recognition of the Minoan tephra in the Acigöl Basin, western Turkey: implications for inter‐archive correlations and fine ash dispersal

Sulpizio

Alçiçek

Zanchetta

et al. 2013

J Quaternary Science

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Here we report the recognition of the Minoan tephra layer in the Acigöl Basin (western Turkey), which represents the most eastward occurrence of this tephra on land and the first in continental deposits out of lacustrine sediments in mainland Turkey. The correlation is supported by glass and mineral geochemistry, which includes solution and laser‐ablation ICP‐MS data for trace and rare earth elements. Thickness and grain size data allow the extension of already described occurrences to an area of about 359 000 km2, from the eastern Mediterranean to Black Sea throughout central–western Turkey. Coupling dispersal area and grain‐size data suggests the joint influence of high and low atmosphere dynamics in dispersal of fine ash during volcanic eruptions. The thickness and lateral continuity of the Minoan tephra in the Acigöl Basin testifies to the widespread impact on the Late Bronze Age environment of mainland Turkey of this important ash deposit. Copyright © 2013 John Wiley & Sons, Ltd.

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The volcanological significance of deep-sea ash layers associated with ignimbrites

Cited by 83 publications

References 22 publications

Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption

Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption

Impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 May 1980 Mount St. Helens fallout deposit

Recognition of the Minoan tephra in the Acigöl Basin, western Turkey: implications for inter‐archive correlations and fine ash dispersal

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