What is the definition of volcanic bombs?

Answer 1

A volcanic bomb is a globule of molten rock (tephra) larger than 65 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Lava bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight. Bombs can be extremely large; the 1935 eruption of Asama in Japan expelled bombs measuring 5-6 m in diameter up to distances of 600 m from the vent.

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

1. Ribbon or cylindrical bombs

These bombs form from highly to moderately fluid magma, ejected as irregular strings and blebs. The strings break up into small segments which fall to the ground intact and look like ribbons. Hence, the name- ribbon bombs. These bombs are circular or flattened in cross section are fluted along length and have tabular vesicles.

2. Spherical bombs

These bombs also form from high to moderately fluid magma. In the case of spherical bombs, surface tension plays a major role in pulling the ejecta into spheres.

3. Spindle, fusiform, or almond/rotational bombs

These bombs are formed by the same processes as spherical bombs, though the major difference being the partial nature of the spherical shape. Spinning during flight leaves these bombs looking elongated or almond shape, the spinning theory behind these bombs' development has also given them the name 'fusiform bombs'. Spindle bombs are characterised by longitudinal fluting, one side slightly smoother and broader than the other. This smooth side represents the underside of the bomb as it fell through the air.

4. Cow-dung bombs

The crudely named cow-dung bombs are formed when highly fluid magma falls from moderate height (so the bomb does not solidify before impact) which are still liquid when they strike the ground. They consequently flatten or splash and form irregular roundish disks which resemble cow-dung.

5. Bread-crust bombs

If the outside of a lava bomb solidifies during its flight, it may develop a cracked outer surface as the interior continues to expand. This type of lava bomb is known as a bread-crust bomb.


6. Cored bombs

Cored bombs are bombs that 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 or in rare cases bits of lava formed earlier during the same eruption.

Volcanic bombs are a significant volcanic hazard, and can cause severe injuries and death to people in an eruption zone. One such incident occurred at Galeras volcano in Colombia in 1993; six people near the summit were killed and several seriously injured by lava bombs when the volcano erupted unexpectedly.

Answer 2

Volcanic Bombs

Answer 3

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What is the definition of volcanic bombs?

Answer 4

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Just to start, volcanic ash is igneous, not metamorphic. Since ash is erupted and travels as particles, the size of the particles can be measured and considered as "grain size". Ash is a variety of "pyroclastic", but by definition, the term "ash" implies a certain size (just like the term "sand" implies size to a geologist). Ash is any pyroclastic with a diameter below 2mm (1/12 of an inch). Lapilli is the term for pyroclasts between 2 - 64 mm, and above that size material is called "volcanic bombs". Pyroclastic material could be considered as an igneous/sedimentary hybrid. The particles are formed from molten material, but travel as particles so can form what is often considered to be sedimentary structures. In any event, volcanic ash and sedimentary mudstones are both considered to be fine grained. But, in both cases, the particles could be so small that you can't really see the individual particles without special equipment.

Answer 5

I love volcanic bombs because when the lava shoots out of the volcano the lava cools in small crystals in mid-air causing a rock called volcanic bomb!

Answer 6

"Volcanic bombs are lava fragments that were ejected while viscous (partially molten) and larger than 64 mm in diameter. Many acquire rounded aerodynamic shapes during their travel through the air. Volcanic bombs include breadcrust bombs, ribbon bombs, spindle bombs (with twisted ends), spheroidal bombs, and "cow-dung" bombs." from USGS website-no copyright.
Photos at website below.
http://volcanoes.usgs.gov/Products/Pglossary/bomb.html