A volcanic block is a fragment of
rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wale ...
that measures more than in diameter and is erupted in a solid condition.
Blocks are formed from material from previous eruptions or from
country rock
Country rock is a music genre that fuses rock and country. It was developed by rock musicians who began to record country-flavored records in the late 1960s and early 1970s. These musicians recorded rock records using country themes, vocal sty ...
and are therefore mostly accessory or accidental in origin. Blocks also occur due to the impact and breakage of
volcanic bombs
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 viscosity, viscous fragments of lava during an eruption. Because volcanic bombs cool a ...
(a bomb is a block with streamlined appearance, often expelled in a molten state). Blocks can also occur due to the disruption of the crust of a lava dome that has formed up or over a vent during an eruption.
Features
Blocks are nearly always angular to sub-angular and roughly equidimensional. If the parent rock is flow-foliated lava, sedimentary material or
schistose
Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...
metamorphic rocks, the blocks may have a plate-like or slab-like form. In other cases, blocks derived from great depths may resemble polished water-worn pebbles and are cobbled due to fluidisation and upwards transport.
Blocks can be enormous and may be transported great distances from the
volcanic vent
A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often fo ...
. The 1924 eruption of
Kīlauea
Kīlauea ( , ) is an active shield volcano in the Hawaiian Islands. It is located along the southeastern shore of Hawaii (island), Hawaii Island. The volcano is between 210,000 and 280,000 years old and grew above sea level about 100,000 years ...
,
Hawaii
Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
, expelled rocks weighing up to 14 tons;
and Mount
Vesuvius
Mount Vesuvius ( ) is a Somma volcano, somma–stratovolcano located on the Gulf of Naples in Campania, Italy, about east of Naples and a short distance from the shore. It is one of several volcanoes forming the Campanian volcanic arc. Vesuv ...
in
Italy
Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
discharged blocks weighing 2-3 tons over distances of 100-200m.
See also
*
*
References
Volcanology
Volcanic rocks
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