earth science

Volcanic bomb

Volcanic bomb 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 bomb rather than just read about it. In short: A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks.

Key takeaways

Volcanic bomb 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 bomb to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Volcanic bomb from memory before moving on to harder problems.

Reference excerpt

A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks. Volcanic bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight. Volcanic bombs can be extremely large; the 1935 eruption of Mount Asama in Japan expelled bombs measuring 5–6 m (16-20 ft) in diameter to a distance up to 600 m (2,000 ft) from the vent. Volcanic bombs are a potentially deadly volcanic hazard in an eruption zone. In an incident at Galeras volcano in Colombia in 1993, six people near the summit were killed and several seriously injured by lava bombs when an eruption broke out unexpectedly. On July 16, 2018, 23 people were injured on a tour boat near the Kilauea volcano by a basketball-sized lava bomb from the Puna eruption. Volcanic bombs occasionally explode from internal gas pressure as they cool, but in most cases, the damage is from impact or subsequent fire. Explosions are most often observed in "bread-crust" type bombs.

Bomb types

Bombs are named according to their shape, which is determined by the fluidity of the magma from which they are formed.

Ribbon or cylindrical bombs form from highly to moderately fluid magma, ejected as irregular strings and blobs. The strings break up into small segments which fall to the ground intact and look like ribbons. They are circular or flattened in cross section, are fluted along their length, and have tabular vesicles. Spherical bombs also form from high to moderately fluid magma, when surface tension pulls the ejecta into spheres. Spindle, fusiform, or almond/rotational bombs are formed by the same processes, but with only a partial spherical shape. Spinning during flight leaves these bombs looking elongated or almond shaped; this theory of their formation has also given them the name 'fusiform bombs'. They are characterised by longitudinal fluting, one side slightly smoother and broader than the other. The smooth side forms as the underside of the bomb during flight. Cow pie or cow dung bombs are formed when highly fluid magma falls from moderate height and is still liquid when it strikes the ground. They flatten or splash to form irregular discs resembling cow dung. Bread-crust bombs form when the outside of a lava bomb solidifies during flight. It may develop a cracked outer surface as the interior continues to expand. Cored bombs have rinds of lava enclosing a core of previously consolidated lava. The core consists of accessory fragments of an earlier eruption, accidental fragments of country rock (such as xenoliths) or occasionally bits of previous lava from the same eruption.

References

External links Media related to Volcanic bombs at Wikimedia Commons USGS Volcano Hazards Program

Illustrations

Worked examples

Example 1 — a first encounter with Volcanic bomb

Start with the simplest possible case. Write down what Volcanic bomb 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 bomb 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 bomb 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 bomb

In research: Volcanic bomb 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 bomb 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 bomb is common in secondary-school and first-year university syllabi. It links to neighbouring topics Tephra, Volcanic rocks, so understanding it makes those chapters shorter.
In everyday life: Look for Volcanic bomb 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 bomb in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Volcanic bomb means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Volcanic bomb out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Volcanic bomb in simple terms?

Why does Volcanic bomb 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 bomb?

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 bomb.