Magmatic eruptions produce
juvenile clasts during
explosive decompression from gas release. They range in intensity from the relatively small
lava fountains on
Hawaii to catastrophic
Ultra-Plinian eruption columns more than high, bigger than the
eruption of Mount Vesuvius in 79 AD that buried
Pompeii. Hawaiian eruptions often begin as a line of vent eruptions along a
fissure vent, a so-called "curtain of fire." These die down as the lava begins to concentrate at a few of the vents. Central-vent eruptions, meanwhile, often take the form of large
lava fountains (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in the air before hitting the ground, resulting in the accumulation of cindery
scoria fragments; when the air is especially thick with
clasts, they cannot cool off fast enough due to the surrounding heat, and hit the ground still hot, the accumulation of which forms
spatter cones. If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long lived;
Puʻu ʻŌʻō, a volcanic cone on
Kilauea, erupted continuously for over 35 years. Another Hawaiian volcanic feature is the formation of active
lava lakes, self-maintaining pools of raw lava with a thin crust of semi-cooled rock.
A'a lava flows are denser and more viscous than pahoehoe, and tend to move slower. Flows can measure thick. A'a flows are so thick that the outside layers cools into a rubble-like mass, insulating the still-hot interior and preventing it from cooling. A'a lava moves in a peculiar way—the front of the flow steepens due to pressure from behind until it breaks off, after which the general mass behind it moves forward. Pahoehoe lava can sometimes become A'a lava due to increasing
viscosity or increasing rate of
shear, but A'a lava never turns into pahoehoe flow. Hawaiian eruptions are responsible for several unique volcanological objects. Small volcanic particles are carried and formed by the wind, chilling quickly into teardrop-shaped
glassy fragments known as
Pele's tears (after
Pele, the Hawaiian volcano deity). During especially high winds these chunks may even take the form of long drawn-out strands, known as
Pele's hair. Sometimes basalt aerates into
reticulite, the lowest density rock type on earth. Volcanoes known to have Hawaiian activity include: • Puʻu ʻŌʻō, a
parasitic cinder cone located on
Kilauea on the
island of Hawaii which erupted continuously from 1983 to 2018. The eruptions began with a -long
fissure-based "curtain of fire" on 3 January 1983. These gave way to centralized eruptions on the site of Kilauea's east rift, eventually building up the cone. Upon reaching the surface, the difference in
air pressure causes the bubble to burst with a loud pop, The relative passivity of Strombolian eruptions, and its non-damaging nature to its source vent allow Strombolian eruptions to continue unabated for thousands of years, and also makes it one of the least dangerous eruptive types. The steady accumulation of small fragments builds
cinder cones composed completely of basaltic
pyroclasts. This form of accumulation tends to result in well-ordered rings of
tephra. Volcanoes known to have Strombolian activity include: •
Parícutin,
Mexico, which erupted from a fissure in a cornfield in 1943. Two years into its life, pyroclastic activity began to wane, and the outpouring of lava from its base became its primary mode of activity. Eruptions ceased in 1952, and the final height was . This was the first time that scientists are able to observe the complete life cycle of a volcano. 2002–2003, and 2009. •
Mount Erebus in
Antarctica, the southernmost active volcano in the world, having been observed erupting since 1972. Eruptive activity at Erebus consists of frequent Strombolian activity. •
Mount Batutara,
Indonesia, exhibited continuous Strombolian eruption since 2014. •
Stromboli itself. The namesake of the mild explosive activity that it possesses has been active throughout historical time; essentially continuous Strombolian eruptions, occasionally accompanied by lava flows, have been recorded at Stromboli for more than a millennium.
Vulcanian . (key: 1.
Ash plume 2.
Lapilli 3.
Lava fountain 4.
Volcanic ash rain 5.
Volcanic bomb 6.
Lava flow 7. Layers of
lava and
ash 8.
Stratum 9.
Sill 10. Magma conduit 11.
Magma chamber 12.
Dike)
Click for larger version. Vulcanian eruptions are a type of volcanic eruption named after the volcano
Vulcano. In Vulcanian eruptions, intermediate
viscous magma within the volcano make it difficult for
vesiculate gases to escape. Similar to Strombolian eruptions, this leads to the buildup of high
gas pressure, eventually popping the cap holding the magma down and resulting in an explosive eruption. Unlike Strombolian eruptions, ejected lava fragments are not aerodynamic; this is due to the higher viscosity of Vulcanian magma and the greater incorporation of
crystalline material broken off from the former cap. They are also more explosive than their Strombolian counterparts, with
eruptive columns often reaching between high. Lastly, Vulcanian deposits are
andesitic to
dacitic rather than
basaltic. Initial Vulcanian activity is characterized by a series of short-lived explosions, lasting a few minutes to a few hours and typified by the ejection of
volcanic bombs and
blocks. These eruptions wear down the
lava dome holding the magma down, and it disintegrates, leading to much more quiet and continuous eruptions. Thus an early sign of future Vulcanian activity is lava dome growth, and its collapse generates an outpouring of
pyroclastic material down the volcano's slope. •
Tavurvur,
Papua New Guinea, one of several volcanoes in the
Rabaul Caldera. •
Anak Krakatoa, Indonesia, repeated vulcanian activities since its rise in 1930 until the present time. Vulcanian eruptions are estimated to make up at least half of all known
Holocene eruptions.
Peléan . (key: 1.
Ash plume 2.
Volcanic ash rain 3.
Lava dome 4.
Volcanic bomb 5.
Pyroclastic flow 6. Layers of
lava and
ash 7.
Stratum 8.
Magma conduit 9.
Magma chamber 10.
Dike)
Click for larger version. Peléan eruptions (or
nuée ardente) are a type of volcanic eruption named after the volcano
Mount Pelée in
Martinique, the site of a Peléan eruption in 1902 that is one of the worst natural disasters in history. In Peléan eruptions, a large amount of gas, dust, ash, and lava fragments are blown out the volcano's central crater, The material collapses upon itself, forming a fast-moving
pyroclastic flow that moves down the side of the mountain at tremendous speeds, often over per hour. These
landslides make Peléan eruptions one of the most dangerous in the world, capable of tearing through populated areas and causing serious loss of life. The
1902 eruption of Mount Pelée caused tremendous destruction, killing more than 30,000 people and completely destroying
St. Pierre, the
worst volcanic event in the 20th century. Peléan eruptions are characterized most prominently by the
incandescent pyroclastic flows that they drive. The mechanics of a Peléan eruption are very similar to that of a Vulcanian eruption, except that in Peléan eruptions the volcano's structure is able to withstand more pressure, hence the eruption occurs as one large explosion rather than several smaller ones. Volcanoes known to have Peléan activity include: •
Mount Pelée,
Martinique. The 1902 eruption of Mount Pelée completely devastated the island, destroying
St. Pierre and leaving only 3 survivors. The eruption was directly preceded by lava dome growth. • The
1951 eruption of Mount Lamington. Prior to this eruption the peak had not even been recognized as a volcano. Over 3,000 people were killed, and it has become a benchmark for studying large Peléan eruptions. •
Mount Sinabung, Indonesia. History of its eruptions since 2013 are showing the volcano emits pyroclastic flows with frequent collapses of its lava domes. File:Pyroclastic flows at Mayon Volcano.jpg|Pyroclastic flows at
Mayon Volcano,
Philippines, 1984 File:Pelee 1902 6.jpg|The
lava spine that developed after the 1902 eruption of
Mount Pelée File:Mount Lamington 1951.jpg|
Mount Lamington following the devastating 1951 eruption File:Mount Sinabung, Indonesia (Unsplash).jpg|2016 eruption of
Mount Sinabung Plinian . (key: 1.
Ash plume 2.
Magma conduit 3.
Volcanic ash rain 4. Layers of
lava and
ash 5.
Stratum 6.
Magma chamber)
Click for larger version. Plinian eruptions (or Vesuvian eruptions) are a type of volcanic eruption named for the historical
eruption of Mount Vesuvius in 79 AD that buried the
Roman towns of
Pompeii and
Herculaneum and, specifically, for its chronicler
Pliny the Younger. The process powering Plinian eruptions starts in the
magma chamber, where
dissolved volatile gases are stored in the magma. The gases
vesiculate and accumulate as they rise through the
magma conduit. These bubbles agglutinate and once they reach a certain size (about 75% of the total volume of the magma conduit) they explode. The narrow confines of the conduit force the gases and associated magma up, forming an
eruptive column. Eruption velocity is controlled by the gas contents of the column, and low-strength surface rocks commonly crack under the pressure of the eruption, forming a flared outgoing structure that pushes the gases even faster. These massive eruptive columns are the distinctive feature of a Plinian eruption, and reach up into the
atmosphere. The densest part of the plume, directly above the volcano, is driven internally by
gas expansion. As it reaches higher into the air the plume expands and becomes less dense,
convection and
thermal expansion of
volcanic ash drive it even further up into the
stratosphere. At the top of the plume, powerful winds may drive the plume away from the
volcano. Plinian eruptions are similar to both Vulcanian and Strombolian eruptions, except that rather than creating discrete explosive events, Plinian eruptions form sustained eruptive columns. They are also similar to Hawaiian
lava fountains in that both eruptive types produce sustained eruption columns maintained by the growth of bubbles that move up at about the same speed as the magma surrounding them. from the 1985 eruption of
Nevado del Ruiz, which totally
destroyed Armero in Colombia The most dangerous eruptive feature are the
pyroclastic flows generated by material collapse, which move down the side of the mountain at extreme speeds It is the model Plinian eruption. Mount Vesuvius has erupted several times since then. Its last eruption was in 1944 and caused problems for the allied armies as they advanced through Italy. • The strongest types of eruptions, with a VEI of 8, are so-called "Ultra-Plinian" eruptions, such as the one at
Lake Toba 74 thousand years ago, which put out 2800 times the material erupted by Mount St. Helens in 1980. •
Hekla in
Iceland, an example of
basaltic Plinian volcanism being its 1947–48 eruption. The past 800 years have been a pattern of violent initial eruptions of
pumice followed by prolonged
extrusion of basaltic lava from the lower part of the volcano. •
Kelud, Indonesia erupted in 2014 and ejected around volcanic ashes which caused economic disruptions across
Java. ==Phreatomagmatic==