Sediment waves and the gravitational stability of explosive eruption columns and ash clouds : towards a new classification of explosive eruptions
Bibliographic record
Abstract
It is increasingly recognized that the gravitational stability of volcanic jets is governed by complex ash-pumice-gas (multiphase) interactions and the mechanics of turbulent entrainment in the lower momentum-driven (fountain) and upper buoyancy-driven (plume) regions of these flows. We use analogue experiments on relatively dense particle-freshwater and particle- saltwater jets injected into a linearly-stratified saltwater layer to revisit, characterize and under- stand how transitions among Buoyant Plume (BP), Total Collapse (TC) and Partial Collapse (PC) multiphase jet regimes in a traditional source strength ( Ri0) - particle concentration ( phi0) parameter space are modified by particle inertial effects expressed through a Stokes number (St) and particle buoyancy effects expressed through a Sedimentation number (Sigma0). We show that “coarse particles” (0.1 ≤ St0 ≤ 10) modify significantly published conditions favouring BP and TC, causing the transition between these endmember regimes to occur smoothly over a PC regime that represents the majority of the Ri0 - phi0 parameter for eruptions. Large volume annular sedimentation waves excited periodically in PC and TC regimes produce terrace deposits and lead to “phoenix clouds” spreading at multiple altitudes. Consistent with most eruptions having fluctuating source strengths, we carry out additional experiments on “unsteady” jets. We identify an additional key source Pulsation number Pu0 and develop a new Ri0 - phi0 - Pu0 parameter space for jet regimes. Applied to volcanic jets generally, and to data we recover from Doppler radar monitoring of two erupting volcanoes, we develop a new set of conceptual models for steady jets in the BP, TC and PC regimes and for unsteady jets in newly defined “Connected Thermals” and Discrete Thermal” regimes, all of which make readily-tested links among source parameters, column heights, sedimentation processes, cloud structures and deposit architectures. The predictions for cloud structures and deposit architectures agree with field-based and remote-sensing observations made for well-studied historic and pre-historic eruptions and explain the origin of common but enigmatic near-field features of explosive eruption deposits. The predictive power of our new Ri0 - phi 0 - Pu0 classification for explosive eruptions provides exciting new pathways for future observational and modelling studies.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".