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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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34 news items

The Seattle Times

The Seattle Times
Wed, 03 Feb 2016 15:29:43 -0800

“That's a volcanic bomb,” he told us. When the mountain blew, photographs showed the vertical eruption that went five miles in the air, but then that cloud came back down, bringing boulders like this one with it, he said. “I've found them as far as 14 ...


Tue, 31 Mar 2015 16:13:47 -0700

NASA scientists studying volcanic rocks from Mars came to the conclusion that the red planet´s volcano, Mount Olympus, is not dead or dormant but in fact an active volcano whose last eruption might have been as recent as a few years to decades ago.

Twin Falls Times-News

Twin Falls Times-News
Sun, 06 Sep 2015 01:03:45 -0700

Astronaut Edgar Mitchell, left, and Apollo 14 Commander Alan Shepard, center, are guided by a geologist at Craters of the Moon in 1969. Astronauts at Craters of the Moon. COURTESY OF NATIONAL PARK SERVICE. Astronauts Eugene Cernan and Joe ...

Center for Research on Globalization

Center for Research on Globalization
Wed, 19 Aug 2015 06:30:00 -0700

The past year or so has been a time of particularly vigorous volcanic activity in Japan, or at least activity that has intruded into public awareness. Perhaps most dramatic was the deadly eruption of Mt. Ontake on September 27, 2014, whose 57 ...

Mother Nature Network

Mother Nature Network
Thu, 23 Apr 2015 08:45:00 -0700

During that historical eruption, the volcano sent deadly 12-inch volcanic bombs into the air, some of which landed nearly 5 miles away. A volcanic bomb is a mass of lava that leaves the volcano in liquid form but cools and hardens into rock before it ...

The Guardian

The Guardian
Tue, 21 Apr 2015 23:10:20 -0700

Japanese lawyers protest the ruling of the Kagoshima district court on Wednesday. Photograph: Jiji Press/AFP/Getty Images. Justin McCurry in Tokyo. Wednesday 22 April 2015 02.10 EDT Last modified on Wednesday 22 April 2015 02.12 EDT. Share on ...

ZME Science

ZME Science
Mon, 12 Jan 2015 09:37:26 -0800

This happens when a volcano violently erupts, creating pockets of air in the rock. The most common types of igneous rocks are: andesite; basalt; dacite; dolerite (also called diabase); gabbro; diorite; peridotite; nepheline; obsidian; scoria; tuff ...
Sat, 10 Jan 2015 11:54:01 -0800

Photo by Hugo Figure 8: Ken Sims and Chris Reveley on summit of Sangay. (Photo by Hugo Cordova) Figure 7: Ken Sims sampling a young volcanic bomb on the summit of Sangay. Figure 9: Ken Sims sampling a recent (likely a few days old) volcanic bomb ...

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