earth science

Volcanic explosivity index

Volcanic explosivity index is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Volcanic explosivity index rather than just read about it. In short: The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G.

Key takeaways

Volcanic explosivity index belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Volcanic explosivity index to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Volcanic explosivity index from memory before moving on to harder problems.

Reference excerpt

The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G. Newhall of the United States Geological Survey and Stephen Self in 1982. Volume of products, eruption cloud height, and qualitative observations (using terms ranging from "gentle" to "mega-colossal") are used to determine the explosivity value. The scale is open-ended with the largest eruptions in history given a magnitude of 8. A value of 0 is given for non-explosive eruptions, defined as less than 10,000 m3 (350,000 cu ft) of tephra ejected; and 8 representing a supervolcanic eruption that can eject 1.0×1012 m3 (240 cubic miles) of tephra and have a cloud column height of over 20 km (66,000 ft). The scale is logarithmic, with each interval on the scale representing a tenfold increase in observed ejecta criteria, with the exception of between VEI-0, VEI-1 and VEI-2.

Classification With indices running from 0 to 8, the VEI associated with an eruption is dependent on how much volcanic material is thrown out, to what height, and how long the eruption lasts. The scale is logarithmic from VEI-2 and up; an increase of 1 index indicates an eruption that is 10 times as powerful. As such, there is a discontinuity in the definition of the VEI between indices 1 and 2. The lower border of the volume of ejecta jumps by a factor of one hundred, from 10,000 to 1,000,000 m3 (350,000 to 35,310,000 cu ft), while the factor is ten between all higher indices. For ejecta volumes above 0.001 km3, the VEI may be calculated as

V E I = ⌊ l o g 10 ( v ) ⌋ + 5 {\displaystyle VEI=\lfloor log_{10}(v)\rfloor +5}

where v {\displaystyle v} is the volume of ejecta in km3. In the following table, the frequency of each VEI indicates the approximate frequency of new eruptions of that VEI or higher.

About 40 eruptions of VEI-8 magnitude within the last 132 million years (Mya) have been identified, of which 30 occurred in the past 36 million years. Considering the estimated frequency is on the order of once in 50,000 years, there are likely many such eruptions in the last 132 Mya that are not yet known. Based on incomplete statistics, other authors assume that at least 60 VEI-8 eruptions have been identified. The most recent is Lake Taupō's Oruanui eruption, more than 27,000 years ago, which means that there have not been any Holocene eruptions with a VEI of 8. There have been at least 10 eruptions of VEI-7 in the last 11,700 years. There are also 58 Plinian eruptions, and 13 caldera-forming eruptions, of large, but unknown magnitudes. By 2010, the Global Volcanism Program of the Smithsonian Institution had cataloged the assignment of a VEI for 7,742 volcanic eruptions that occurred during the Holocene (the last 11,700 years) which account for about 75% of the total known eruptions during the Holocene. Of these 7,742 eruptions, about 49% have a VEI of 2 or lower, and 90% have a VEI of 3 or lower.

Limitations Under the VEI, ash, lava, lava bombs, and ignimbrite are all treated alike. Density and vesicularity (gas bubbling) of the volcanic products in question is not taken into account. In contrast, the DRE (dense-rock equivalent) is sometimes calculated to give the actual amount of magma erupted. Another weakness of the VEI is that it does not take into account the power output of an eruption, which makes the VEI extremely difficult to determine with prehistoric or unobserved eruptions. Although VEI is quite suitable for classifying the explosive magnitude of eruptions, the index is not as significant as sulfur dioxide emissions in quantifying their atmospheric and climatic impact.

Lists of notable eruptions

Timeline of volcanism on Earth (mostly VEI-6, within 2 kya) List of volcanic eruptions 1500–2000 List of volcanic eruptions in the 21st century List of volcanic eruptions by death toll List of large Holocene volcanic eruptions (VEI-5–7) List of large volcanic eruptions (VEI-5–8, within 450+ Mya) List of largest volcanic eruptions (VEI-7–8, mostly within 500 Mya)

See also Supervolcano – Volcano that has erupted with a volcanic explosivity index of 8 Decade Volcanoes – Set of volcanoes considered especially dangerous Dispersal index – Indicator of spread of volcanic ejecta Lists of volcanoes List of natural disasters by death toll

References

External links VEI glossary entry from a USGS website How to measure the size of a volcanic eruption, from The Guardian The size and frequency of the largest explosive eruptions on Earth, a 2004 article from the Bulletin of Volcanology List of Large Holocene Eruptions (VEI > 4) from the Smithsonian Global Volcanism Program Archived 2012-01-17 at the Wayback Machine

Illustrations

Worked examples

Example 1 — a first encounter with Volcanic explosivity index

Start with the simplest possible case. Write down what Volcanic explosivity index claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Volcanic explosivity index before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Volcanic explosivity index ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Volcanic explosivity index

In research: Volcanic explosivity index appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Volcanic explosivity index in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Volcanic explosivity index is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1982 introductions, Hazard scales, Volcanology, so understanding it makes those chapters shorter.
In everyday life: Look for Volcanic explosivity index outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Volcanic explosivity index in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Volcanic explosivity index means in your own words.
Compare your version with the excerpt and mark what you missed.
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Frequently asked questions

What is Volcanic explosivity index in simple terms?

The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G.

Why does Volcanic explosivity index matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Volcanic explosivity index?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Volcanic explosivity index.