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Fusiform lava bomb. Capelinhos Volcano, Faial Island, Azores.
Volcanic bomb found in the Cinder Cones region of the Mojave National Preserve.
Volcanic bomb at Vulcania (Puy-de-Dôme)

A volcanic bomb is a mass of molten rock (tephra) larger than 64 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. Because volcanic bombs cool after they leave the volcano, they do not have grains making them extrusive igneous rocks. Volcanic 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 Mount Asama in Japan expelled bombs measuring 5–6 m in diameter up to 600 m from the vent. 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.

Volcanic bombs are known to occasionally explode from internal gas pressure as they cool, but contrary to some claims in popular culture (specifically, the 1997 film Volcano), explosions are rare; in most cases most of the damage they cause is from impact, or subsequent fire damage. Bomb explosions are most often observed in 'bread-crust' type bombs.

Types of bombs[edit]

Various volcanic bombs in the National Museum of Nature and Science, Tokyo, Japan.

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. Hence, the name "ribbon bombs". These bombs 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. In the case of spherical bombs, surface tension plays a major role in pulling the ejecta into spheres.
  • Spindle, fusiform, or almond/rotational 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 shaped; 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.
  • Cow pie bombs are formed when highly fluid magma falls from moderate height, so the bombs do not solidify before impact (they are still liquid when they strike the ground). They consequently flatten or splash and form irregular roundish disks, which resemble cow-dung.
  • Bread-crust bombs are formed if the outside of the lava bombs solidifies during their flights. They may develop cracked outer surfaces as the interiors continue to expand.
  • 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.


External links[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Volcanic_bomb — Please support Wikipedia.
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22 news items


Sat, 10 Jan 2015 11:54:01 -0800

Figure 9: Ken Sims sampling a recent (likely a few days old) volcanic bomb on the summit of Sangay. (Photo by Hugo Cordova) Figure 10: Raul Tenemaza Flores, Chris Reveley, Ken Sims and Hugo Cordova exploring Figure 10: Raul Tenemaza Flores, Chris ...

The Guardian

The Guardian
Tue, 09 Dec 2014 06:18:24 -0800

Winds of up to 80mph causing exceptionally large waves are expected to bring dangerous conditions to the west coast of Britain, the Met Office has warned. The severe weather, which is expected to hit the UK overnight on Tuesday and could disrupt travel ...

Ars Technica

Ars Technica
Mon, 01 Sep 2014 13:17:47 -0700

The destruction was horrific. Most of the fatalities were inflicted by pyroclastic flows, crushed buildings and volcanic bomb impacts. Then, in 1994, after more than half a century of quiet, exactly the same thing happened. Vulcan and Tavurvur erupted ...


Tue, 02 Sep 2014 05:10:04 -0700

The destruction was horrific. Most of the fatalities were inflicted by pyroclastic flows, crushed buildings and volcanic bomb impacts. Then, in 1994, after more than half a century of quiet, exactly the same thing happened. Vulcan and Tavurvur erupted ...

Natural History Museum (blog)

Natural History Museum (blog)
Wed, 28 Jan 2015 07:00:00 -0800

On other occasions, it might not be garbage, but a proper treasure that you dig out: A volcanic bomb! Hard-rock geologists, get your hammers and cameras ready! Pumice.jpg. And this is what you get if you repeat the above steps for a whole week. Now ...


Tue, 21 Oct 2014 22:22:45 -0700

The highest number of buyers online is for zameen chakkars, sparklers and anaars. It is not that the noisy ones are being avoided. The volcanic bomb aka rassi bomb has had a 30 percent fall in demand due to its ear-popping sound but is still sold out ...
Mon, 31 Mar 2014 16:11:04 -0700

... from and larger than any of the currently known types of dinos, but likely related to a subspecies of Diplodocus hallorum, a giant plant-eater with exceptionally strong built skeleton (perhaps able to withstand even moderately large volcanic bomb ...
Auckland stuff.co.nz
Wed, 09 Apr 2014 22:37:30 -0700

University of Canterbury geologists are planning to test the theory that the best way to avoid flying volcanic rocks is to face an eruption, rather than run from it. In an experiment that sounds like something out of the fun science television ...

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