A Vulcanian eruption is a type of volcanic eruption characterized by a dense cloud of ash-laden gas exploding from the crater and rising high above the peak. They usually commence with

phreatomagmatic eruption Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions cont ...

s which can be extremely noisy due to the rising magma heating water in the ground. This is usually followed by the explosive clearing of the vent and the

eruption column An eruption column or eruption plume is a cloud of super-heated Volcanic ash, ash and tephra suspended in volcanic gas, gases emitted during an explosive eruption, explosive volcanic eruption. The volcanic materials form a vertical column or Plu ...

is dirty grey to black as old weathered rocks are blasted out of the vent. As the vent clears, further ash clouds become grey-white and creamy in colour, with convolutions of the ash similar to those of

Plinian eruptions Plinian eruptions or Vesuvian eruptions are Volcano, volcanic Types of volcanic eruptions, eruptions characterized by their similarity to the eruption of Mount Vesuvius in 79 AD, which destroyed the ancient Roman cities of Herculaneum and Pompei ...

. The term ''Vulcanian'' was first used by

Giuseppe Mercalli Giuseppe Mercalli (21 May 1850 – 19 March 1914) was an Italian volcanologist and Catholic priest. He is known best for the Mercalli intensity scale for measuring earthquake intensity. Biography Born in Milan, Mercalli was ordained a Roman ...

, witnessing the 1888–1890 eruptions on the island of

Vulcano Vulcano () or Vulcan is a small volcanic island belonging to Italy in the Tyrrhenian Sea, about north of Sicily and located at the southernmost end of the seven Aeolian Islands. The island is known for its volcanic activity and contains severa ...

. His description of the eruption style is now used all over the world. Mercalli described Vulcanian eruptions as "...Explosions like cannon fire at irregular intervals..." Their explosive nature is due to increased

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

content of the magma. Almost all types of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

can be involved, but magma with about 55% or more silica (e.g.

basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Ameri ...

) is most common. Increasing silica levels increase the viscosity of the magma which means increased explosiveness.

Characteristics

Vulcanian eruptions display several common characteristics. The mass of rock ejected during the eruption is usually between 10² and 10⁶ tonnes and contains a high proportion of non-juvenile material (> 50%). During active periods of volcanic activity, intervals between explosions vary from less than 1 minute (e.g.

Anak Krakatoa Anak KrakatauEnglish translation and common name: ''Child of Krakatoa'' is a volcanic island in Indonesia. On 29 December 1927, Anak Krakatau first emerged from the caldera formed in 1883 by the explosive volcanic eruption that destroyed the ...

) to about a day. Pyroclastic flows are also common features of this type of eruption. The gas streaming phase of Vulcanian eruptions are characterised by discrete cannon-like explosions. These expulsions of gas can reach supersonic velocities resulting in shock waves.Nairn, I.A. & Self, S.J., 1978, ''Journal of Volcanology and Geothermal Research'', 3, 39–60 The

tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...

is dispersed over a wider area than that from

Strombolian eruptions In volcanology, a Strombolian eruption is a type of volcanic eruption with relatively mild blasts, typically having a Volcanic Explosivity Index of 1 or 2. Strombolian eruptions consist of ejection of incandescent cinders, lapilli, and volcanic b ...

. The

pyroclastic rock Pyroclastic rocks are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroclasts. Pyroclastic rocks are a type of volcaniclastic deposit, which are deposit ...

and the base surge deposits form an ash

volcanic cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and s ...

, while the ash covers a large surrounding area. The eruption ends with a flow of viscous

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

. Vulcanian eruptions may throw large metre-size blocks several hundred metres, occasionally up to several kilometres. Vulcanian eruptions are dangerous to persons within several hundred metres of the vent.

Volcanic bomb 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 l ...

s are common products of this type of eruption. These are initially molten blobs of lava, which rapidly cool into blocks often 2 to 3 m across. At

Galeras Galeras (Urcunina among the 16th-century indigenous people) is an Andean stratovolcano in the Colombian department of Nariño, near the departmental capital Pasto. Its summit rises above sea level. It has erupted frequently since the Spanish ...

, a Vulcanian eruption ejected bombs which struck several volcanologists who were in the crater, some of whom died or suffered severe injuries. image:Gran Cratere Vulcano.jpg, The Gran Cratere,

. A sense of scale is provided by the tourist visible near the centre of the crater.

1930 eruption of Stromboli

The 11 September 1930 eruption of Stromboli was a Vulcanian eruption. It started at 08:10 hours (local), when ash was vented for about 10 minutes. Then at 09:52 two incredibly powerful explosions occurred which shook the whole

island An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been ...

. Blocks were hurled about 2 km. These fell out of the sky smashing through buildings etc. A

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

2 to 2.5 m high was generated. By 10:40 the explosive phase of the eruption was over. Expulsion of lava followed, this flowed down the Sciara del Fuoco, lasting into the night. At the same time incandescent

scoria Scoria or cinder is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackso ...

flowed down the Vallonazzo Valley and entered the sea near Piscità. It is believed that water entered due to a partial collapse of the conduit. The water flashed into steam and took the easiest "escape route" via the open conduit. Expansion by contact with the molten magma generated the two very large explosions. There were six deaths. Four fishermen died at sea when the avalanches of hot scoria caused the sea to become very disturbed. One person was killed in Stromboli village by falling blocks, and the sixth was killed by the tsunami.

References

External links

Kinds of volcanic eruptions
{{Types of volcanic eruptions he:התפרצות געשית#סוגי התפרצות געשית

Characteristics

1930 eruption of Stromboli

See also

References

Further reading

External links