(WORKING DRAFT) VEI: Suggestions for Improving Clarity in Eruption Reporting
Introduction
The Volcanic Explosivity Index (VEI) has long served as a widely recognized numerical framework for describing volcanic eruptions, providing a standard reference across scientific literature, hazard assessments, media reporting, and public discourse (Newhall and Self, 1982). Its original strength lay in its simplicity: a logarithmic scale from 0 to 8 that enabled broad comparison of eruptive events across many orders of magnitude. VEI was designed as a pragmatic, semi-quantitative estimate of explosive eruption magnitude, drawing on Walker’s concepts of magnitude and intensity (Walker, 1973), anchored where possible in erupted volume and eruption column height, and supplemented by qualitative criteria when those parameters were uncertain or unavailable.
Over time, however, the scope of interpretation applied to VEI has expanded beyond its intended role. VEI values are now frequently treated as proxies not only for eruption magnitude, but also for eruption style, fragmentation efficiency, sulfur dioxide emissions, climatic relevance, and hazard severity. This semantic broadening emerged gradually through usage rather than formal definition, resulting in a single numerical value being asked to represent multiple aspects of eruptive behavior that are not uniquely linked and do not scale together consistently.
As a result, eruptions assigned similar VEI values may differ substantially in eruption rate, fragmentation behavior, volatile release, and post-eruptive consequences. In contrast, eruptions with markedly different VEI values may produce comparable atmospheric or environmental effects. These ambiguities do not reflect deficiencies in the VEI framework itself, but rather the consequences of using a magnitude-oriented index as shorthand for distinct physical, temporal, and ecological dimensions.
Rather than replacing or redefining VEI, this work introduces an additive and explicitly decoupled revision, informally referred to as VEI 2.0, that preserves the original VEI magnitude number while providing optional parallel descriptors for parameters VEI cannot uniquely encode. VEI 2.0 separates eruptive description into three complementary components: the legacy VEI numerical magnitude classification (0–8), an alphabetical long-term impact classification describing post-eruptive Earth-system response when such effects are constrained, and an eruption type designation describing the dominant eruptive mechanism. Each component is defined independently and may be reported alone or in combination, depending on data availability.
Additionally, this work adopts the term Volcanic Eruptive Index rather than Volcanic Explosivity Index while retaining the established acronym VEI. This change is not intended to redefine the original framework, but to reduce semantic ambiguity introduced by the term explosivity, which is commonly interpreted as a proxy for eruption style, hazard severity, or fragmentation efficiency. The term “eruptive” more accurately reflects how VEI is used in practice: as a comparative descriptor of eruptive events across a broad spectrum of mechanisms, including both explosive and effusive activity.
By restoring clear conceptual boundaries between magnitude, impact, and eruptive mechanism, VEI 2.0 retains the communicative strengths of the original framework while improving interpretive clarity and flexibility. The goal is not to increase complexity, but to allow each descriptor to convey precisely what it is designed to measure—no more and no less—while accommodating uncertainty, incomplete records, and the diversity of volcanic behavior observed across Earth history.
What VEI Measures
The Volcanic Explosivity Index (VEI) was conceived as a comparative framework for ranking explosive eruptions across many orders of magnitude, using a logarithmic scale that allows events of vastly different size to be discussed within a single reference system (Newhall and Self, 1982). VEI was designed as a pragmatic, semi-quantitative estimate of explosive eruption magnitude, drawing on Walker’s concepts of magnitude and intensity, and anchored where possible in erupted volume and eruption column height. Where those parameters are poorly constrained, VEI permits the use of supplementary qualitative criteria as proxies for eruptive scale.
Because of this design, VEI is most robust when interpreted as a magnitude-oriented index rather than as a comprehensive descriptor of eruptive behavior. Although VEI may reflect intensity or destructiveness in a composite sense when the observational record allows, it cannot uniquely encode eruption rate, fragmentation efficiency, volatile release, sulfur dioxide output, or downstream effects such as climate forcing or hazard severity. While some of these factors may correlate with eruption magnitude in specific contexts, they do not do so consistently or uniquely. Eruptions assigned similar VEI values may differ substantially in magma composition, conduit dynamics, degassing behavior, and atmospheric interaction, producing markedly different physical expressions and environmental consequences despite sharing the same VEI classification.
The historical reliance on erupted volume and column height reflects a practical constraint. These are among the few parameters that can be estimated for both historical and prehistoric eruptions, enabling VEI to function across deep time as well as within modern observational records. This utility, however, comes with an inherent limitation: magnitude proxies alone cannot capture the diversity of eruptive processes that govern fragmentation behavior, eruption rate, volatile release, or the persistence of post-eruptive effects.
Over time, the use of shorthand has blurred these distinctions. VEI values are frequently described using eruption-style terminology, for example, treating certain VEI ranges as implicitly “Plinian” or “effusive,” even though the eruptive mechanism is neither uniquely determined by erupted volume nor formally defined by the VEI number. Although Newhall and Self (1982) included qualitative style descriptors as supporting criteria, eruption type cannot be reliably inferred from VEI alone, and such practices introduce ambiguity by attributing mechanistic meaning to a parameter that was never designed to encode it uniquely.
Recognizing these limitations does not diminish the value of the original VEI framework. Instead, it clarifies its proper role. VEI provides a standardized, semi-quantitative measure of eruption magnitude, not a complete description of how an eruption unfolded, what mechanism dominated, or what long-term effects followed. When used within these bounds, VEI remains a robust comparative tool. Difficulties arise only when those bounds are implicitly expanded.
Establishing this distinction is a prerequisite for developing VEI 2.0. Rather than redefining eruption magnitude or replacing the existing VEI scale, VEI 2.0 preserves the original VEI number and introduces optional, explicitly decoupled descriptors that may be appended when additional information is available. Long-term Earth-system impact and eruption type are treated as independent dimensions, each defined by the phenomena they describe. By separating these parameters rather than forcing them into a single metric, VEI 2.0 preserves the original index’s communicative strengths while restoring conceptual clarity and flexibility. The goal is not to complicate eruption classification, but to ensure that each descriptor conveys precisely what it measures—no more and no less.
The Problem of Conflation and the Limits of a Single Axis
A persistent source of confusion in the use of VEI arises from the implicit assumption that eruption magnitude, intensity, and consequences are interchangeable or can be adequately represented on a single dimension. In practice, these parameters overlap only partially. Eruption magnitude, as indicated by erupted volume and column height proxies, captures the overall scale of material output, but it does not uniquely characterize fragmentation efficiency, eruption rate, volatile release, or the duration and persistence of atmospheric and environmental effects.
This limitation becomes increasingly apparent at both ends of the eruptive spectrum. Low-volume eruptions may exhibit extreme short-lived explosivity, while high-volume eruptions may unfold gradually, distributing mass and energy over extended durations with comparatively muted instantaneous discharge. Similarly, long-term climatic and environmental impacts depend not only on erupted volume, but also on factors such as sulfur dioxide emissions, injection height relative to the tropopause, eruption duration, and the interaction between eruptive products and atmospheric circulation.
The widespread tendency to associate specific eruption styles or impact expectations with VEI values reflects an attempt to extract information that the index cannot uniquely supply. In effect, eruption style, intensity, and consequence have been informally folded into the VEI, producing a hybrid interpretation that varies across disciplines and contexts. This practice obscures meaningful differences between eruptions that share similar magnitudes but differ fundamentally in physical behavior and long-term influence.
Further subdividing eruption styles does not resolve these challenges within the numerical scale, nor does it redefine existing VEI categories. Instead, they point to a structural limitation: a single axis cannot simultaneously encode eruptive magnitude, energetic intensity, and long-term impact without sacrificing clarity or consistency.
VEI 2.0 addresses this limitation not by redefining the VEI numerical scale, but by preserving the established VEI number for continuity while explicitly separating the additional dimensions that have historically been embedded within it. Newhall and Self (1982) defined VEI as a pragmatic composite estimate that incorporates magnitude proxies and qualitative descriptors to accommodate incomplete observational records. While this approach enabled broad applicability, it also introduced an inherent ambiguity: the VEI number can be interpreted as reflecting multiple partially overlapping properties without clearly specifying which dimension is being emphasized.
This work retains the familiar VEI number as a magnitude-oriented reference for backward compatibility but relocates eruptive mechanism and long-term Earth-system response into independent, optional descriptors. Eruption type is treated as a standardized archetype designation describing the dominant eruptive mechanism, while long-term impact is expressed as a separate classification describing persistence and system response when such effects are constrained. Together, these components convey more information than any single axis can supply, without altering the meaning or usability of the original VEI scale.
Conceptual Structure of VEI 2.0
VEI 2.0 describes volcanic eruptions using a set of independent but complementary descriptors, each corresponding to a distinct aspect of eruptive behavior. Rather than relying on a single metric to encode multiple phenomena, the framework separates eruptive description into eruption magnitude (as expressed by the legacy VEI), long-term Earth-system impact, and eruption type.
VEI 2.0 retains the legacy VEI number for continuity but interprets it explicitly as an intensity-class label rather than a pure magnitude metric, reflecting the composite nature of VEI as originally defined by Newhall and Self, 1982. VEI 2.0 preserves this established usage while avoiding the assumption that the number uniquely encodes eruption rate, fragmentation efficiency, volatile release, or long-term consequences.
The alphabetical component represents long-term impact, describing the persistence and Earth-system response following an eruption when such effects are constrained. Impact classes are based on recovery behavior and system feedback rather than fixed durations and may be assigned independently of the VEI number when sufficient evidence exists. Higher classes reflect regime-level perturbations, with the highest class reserved for chronic boundary-condition changes arising from prolonged or cumulative forcing.
The eruption type designation provides a mechanistic description of the dominant eruptive archetype, based on eruption processes, vent architecture, and magma–conduit interaction. Type designations are descriptive rather than ordinal and do not imply magnitude, intensity, or impact.
Each component of VEI 2.0 may be reported alone or in combination, depending on data availability and analytical context. This structure allows eruptions to be compared along specific dimensions without conflating magnitude, mechanism, and consequence within a single index.
Eruption-Type Designator Expansion
The eruption-type designators used in VEI 2.0 are intended to function as descriptive archetypes rather than exhaustive mechanistic categories. All widely used eruption styles are included for continuity (e.g., Hawaiian, Strombolian, Vulcanian, Plinian), but additional types are introduced to address eruptive mechanisms that are poorly represented or absent in common VEI shorthand usage. These include compositionally or structurally distinct endmembers such as carbonatite volcanism (Doinyan) and pipe-forming ultramafic systems (Kimberlian), as well as large-scale fissure-fed effusive provinces such as flood basalts and large igneous provinces (Deccan).
In addition, the informal term “Ultra-Plinian” is replaced with the archetype name “Tamboran” to avoid intensity-coded language and to anchor the largest sustained column-forming explosive endmember to a widely recognized historical example. Tamboran is not intended as a distinct mechanistic category from Plinian, but rather as an archetypal label for the upper-end sustained-column endmember, which is frequently treated as distinct in legacy VEI charts. This naming convention preserves interpretive clarity while keeping the type index extensible as additional mechanisms warrant formal inclusion.
Large igneous province volcanism is represented in the type index using the archetype name “Deccan,” reflecting both its broad recognizability and its historical role as a reference example of province-scale fissure-fed effusive emplacement. The Siberian Traps represent an equally important endmember and are strongly linked to the Permian–Triassic mass extinction; however, “Siberian” carries additional geographic and historical connotations that may complicate its use as a neutral archetype label in general reporting contexts. “Deccan” is therefore adopted as the representative name for large igneous province-style volcanism in VEI 2.0, while the type designation is intended to encompass the full range of LIP systems, including the Siberian Traps and other provinces.
The “Helenean” designator is introduced to represent collapse-driven explosive eruptions in which edifice failure and rapid decompression produce a directed lateral blast that strongly governs the initial eruptive expression. Although such events may transition into sustained vertical explosive activity, the opening collapse-and-blast phase represents a distinct eruptive mechanism with eruptive dynamics and deposit architecture that differ fundamentally from column-dominated Plinian behavior. Mount St. Helens (1980) is used as the archetype because it is the best documented and most widely recognized example in the modern observational record.
Type designators describe eruptive mechanism and vent architecture, not magnitude, intensity, or long-term impact. Morphologic outcomes, such as caldera collapse, are treated as consequences of eruptive withdrawal and are not classified as eruption types in VEI 2.0.
Reporting and Usage Conventions
VEI 2.0 is designed to be reported in plain-language form, prioritizing clarity, memorability, and ease of communication across scientific, educational, and public-facing contexts. Rather than relying on dense symbolic notation or specialized shorthand, VEI 2.0 classifications are expressed as a concise verbal sequence combining the VEI number, long-term impact (when known), and eruption type.
The recommended reporting format is:
VEI [Intensity][Impact] [Type]
For example:
- VEI 1A Surtseyan
- VEI 4 Plinian
- VEI 5D Helenean
In this format, the numerical value is the original VEI classification (0–8), retained for continuity with existing literature and datasets. The optional alphabetical character represents long-term impact when constrained, and the eruption type is stated explicitly using standardized archetype terminology. When long-term impacts are unknown or unconstrained, the alphabetical component is omitted rather than inferred.
This reporting style is intentionally plain-language and non-cryptic. By using natural word order and familiar terminology, VEI 2.0 avoids the need for memorization of notation rules and reduces the likelihood of misinterpretation by nonspecialists. The format is equally suitable for formal publications, monitoring reports, classroom instruction, and media communication.
Optional components and partial reporting
Not all components of VEI 2.0 must be reported in every case. The framework is explicitly designed to accommodate incomplete or evolving information:
- Intensity (numerical value) may be reported independently when eruptive vigor is constrained.
- Impact (alphabetical class) is reported only when post-eruptive Earth-system effects are sufficiently documented.
- Eruption type is reported when the dominant eruptive mechanism is identifiable.
Absence of an impact classification does not imply minimal or negligible effects; it reflects uncertainty or insufficient evidence at the time of reporting.
Complex and multi-phase eruptions
Many eruptions exhibit multiple eruptive styles or evolve over time. In such cases, the reported eruption type reflects the dominant mechanism associated with the described phase or interval. Where appropriate, different phases of a single eruption may be described separately using the same reporting format.
VEI 2.0 classifications are descriptive and subject to revision as new observational, geochemical, or proxy data become available. Updates to intensity, impact, or type should be viewed as refinements rather than corrections, reflecting improved constraint rather than reinterpretation of the underlying framework.
Worked Examples
The following examples illustrate how VEI 2.0 describes eruptive behavior using independent descriptors for intensity, long-term impact, and eruption type. Each case highlights a scenario in which traditional VEI classifications are ambiguous or incomplete and demonstrates how decoupling improves clarity without increasing complexity.
Example 1: Surtsey, Iceland (1963–1967)
The eruption of Surtsey began as a submarine event driven by intense magma–water interaction, producing explosive activity dominated by phreatomagmatic processes. Early phases were characterized by repeated ash-rich explosions and rapid island construction, followed by later effusive activity as the vent emerged above sea level (Thorarinsson et al., 1964; Moore, 1985).
Eruptive output during the explosive phase was modest, with low erupted volume and limited column development. Long-term environmental effects were primarily local, despite the eruption’s outsized scientific importance for studies of island formation and ecological succession.
Using VEI 2.0, this eruption can be described as:
VEI 1A Surtseyan
This classification captures the low VEI magnitude and transient impact while explicitly identifying magma–water interaction as the dominant mechanism, without implying greater explosivity or long-term consequence than the event produced.
Example 2: Mount St. Helens, United States (1980)
The 1980 eruption of Mount St. Helens was initiated by catastrophic edifice failure, leading to rapid decompression and a laterally directed blast, followed by sustained explosive activity and prolonged dome growth. Eruptive behavior evolved, but the opening phase was dominated by collapse-driven processes rather than sustained vertical column development (Lipman and Mullineaux, 1981).
The eruption exhibited high VEI magnitude during its opening stages, with substantial fragmentation and high eruption columns. Long-term impacts included multi-year environmental disturbance and measurable ecological and geomorphic effects at regional scales, though global climatic forcing was limited.
Within the VEI 2.0 framework, the dominant eruptive phase may be described as:
VEI 5C Helenean
This description distinguishes the collapse-driven eruptive mechanism from the VEI number and the impact class, avoiding the assumption that the eruption conforms neatly to sustained-column Plinian behavior while still conveying both eruption magnitude and persistence. It explicitly identifies directed blast as the dominant mechanism, without implying greater explosivity or long-term consequences than those produced by the event.
Example 3: Tambora, Indonesia (1815)
The 1815 eruption of Tambora represents an end-member explosive event, characterized by sustained eruption columns, widespread tephra dispersal, and profound atmospheric effects. The eruption produced extreme mass discharge and vigorous fragmentation, and it generated a multi-year perturbation to global climate systems.
VEI magnitude was exceptionally high, and eruption columns reached the stratosphere. Post-eruptive impacts persisted for multiple years and included hemispheric-to-global climatic anomalies, most notably the “Year Without a Summer” (Self et al., 1984; Stothers, 1984).
Under VEI 2.0, this eruption is expressed succinctly as:
VEI 7E Tamboran
This classification, in plain language, conveys the extreme VEI magnitude, high-impact persistence, and sustained column-forming eruptive mechanism, without relying on the VEI number alone to imply climatic consequences.
Conclusions
The Volcanic Explosivity Index has long provided a shared vocabulary for discussing volcanic eruptions, but its widespread use has increasingly blurred the distinction between eruption magnitude, eruptive mechanism, and long-term consequences. VEI 2.0 addresses this limitation not by replacing the original index, but by reorganizing eruptive description into explicitly decoupled components that reflect how eruptions differ in practice.
By preserving the original VEI numerical classification while separating long-term Earth-system impact and eruption type into independent descriptors, VEI 2.0 restores conceptual clarity without sacrificing the communicative strengths that led to VEI’s widespread adoption. Each component is defined by the phenomenon it describes, allowing eruptions to be compared along specific dimensions without implying equivalence across others. Optional reporting of long-term impact further accommodates uncertainty, incomplete records, and evolving interpretations without forcing premature classification.
The introduction of distinct regime-level impact classes enables VEI 2.0 to differentiate between abrupt climatic shocks and chronic Earth-system restructuring, a distinction that is particularly important when comparing explosive eruptions with large igneous province volcanism. Plain-language reporting conventions further enhance accessibility, enabling clear communication of VEI 2.0 classifications across scientific, educational, and public contexts.
VEI 2.0 is intended as a descriptive framework, not a predictive tool or hazard metric. Its strength lies in its flexibility, transparency, and resistance to semantic overload. By allowing each descriptor to convey exactly what it is designed to represent, VEI 2.0 provides a durable and adaptable language for describing volcanic eruptions across Earth’s history, while remaining open to refinement as new data and perspectives emerge.
References
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Feedback and discussion are welcome; this draft is intended to evolve prior to formal submission.
Last Updated on 7 February 2026 by Angel Doran