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 30 km (19 mi) high, bigger than the eruption of Mount Vesuvius in 79 that buried Pompeii.[1]
Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of very fluid basalt-type lavas with low gaseous content.
The volume of ejected material from Hawaiian eruptions is less than
half of that found in other eruptive types. Steady production of small
amounts of lava builds up the large, broad form of a shield volcano.
Eruptions are not centralized at the main summit as with other volcanic
types, and often occur at vents around the summit and from fissure vents radiating out of the center.[4]
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; however, 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 cinder cone of Kilauea, has been erupting continuously since 1983. 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; there are currently only 5 such lakes in the world, and the one at Kīlauea's Kupaianaha vent is one of them.[4]
Flows from Hawaiian eruptions are basaltic, and can be divided into two types by their structural characteristics. Pahoehoe
lava is a relatively smooth lava flow that can be billowy or ropey.
They can move as one sheet, by the advancement of "toes," or as a
snaking lava column. A'a
lava flows are denser and more viscous then pahoehoe, and tend to move
slower. Flows can measure 2 to 20 m (7 to 66 ft) 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.[10]
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.[4]
Although Hawaiian eruptions are named after the volcanoes of Hawaii, they are not necessarily restricted to them; the largest lava fountain ever recorded formed on the island of Izu Ōshima (on Mount Mihara) in 1986, a 1,600 m (5,249 ft) gusher that was more than twice as high as the mountain itself (which stands at 764 m (2,507 ft)).[4][11]
Volcanoes known to have Hawaiian activity include:
Strombolian eruptions are a type of volcanic eruption, named after the volcano Stromboli, which has been erupting continuously for centuries.[12] Strombolian eruptions are driven by the bursting of gas bubbles within the magma. These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slugs. These grow large enough to rise through the lava column.[13] Upon reaching the surface, the difference in air pressure causes the bubble to burst with a loud pop,[12] throwing magma in the air in a way similar to a soap bubble. Because of the high gas pressures associated with the lavas, continued activity is generally in the form of episodic explosive eruptions accompanied by the distinctive loud blasts.[12] During eruptions, these blasts occur as often as every few minutes.[14]
The term "Strombolian" has been used indiscriminately to describe a wide variety of volcanic eruptions, varying from small volcanic blasts to large eruptive columns. In reality, true Strombolian eruptions are characterized by short-lived and explosive eruptions of lavas with intermediate viscosity, often ejected high into the air. Columns can measure hundreds of meters in height. The lavas formed by Strombolian eruptions are a form of relatively viscous basaltic lava, and its end product is mostly scoria.[12] 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.[14]
Strombolian eruptions eject volcanic bombs and lapilli
fragments that travel in parabolic paths before landing around their
source vent. 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.[12]
Strombolian eruptions are similar to Hawaiian eruptions, but there are differences. Strombolian eruptions are noisier, produce no sustained eruptive columns, do not produce some volcanic products associated with Hawaiian volcanism (specifically Pele's tears and Pele's hair), and produce fewer molten lava flows (although the eruptive material does tend to form small rivulets).[12][14]
Volcanoes known to have Strombolian activity include:
Vulcanian eruptions are a type of volcanic eruption, named after the volcano Vulcano.[20] It was named so following Giuseppe Mercalli's observations of its 1888-1890 eruptions.[21] In Vulcanian eruptions, highly 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. However, unlike Strombolian eruptions, ejected lava
fragments are not aerodynamic; this is due to the higher viscosity of
Vulcanian magma and the greate
Hawaiian
Main article: Hawaiian eruption
Diagram of a Hawaiian eruption. (key: 1. Ash plume 2. Lava fountain 3. Crater 4. Lava lake 5. Fumaroles 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.
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; however, 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 cinder cone of Kilauea, has been erupting continuously since 1983. 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; there are currently only 5 such lakes in the world, and the one at Kīlauea's Kupaianaha vent is one of them.[4]
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.[4]
Although Hawaiian eruptions are named after the volcanoes of Hawaii, they are not necessarily restricted to them; the largest lava fountain ever recorded formed on the island of Izu Ōshima (on Mount Mihara) in 1986, a 1,600 m (5,249 ft) gusher that was more than twice as high as the mountain itself (which stands at 764 m (2,507 ft)).[4][11]
Volcanoes known to have Hawaiian activity include:
- Puʻu ʻŌʻō, a parasitic cinder cone located on Kilauea on the island of Hawaiʻi which has been erupting continuously since 1983. The eruptions began with a 6 km (4 mi)-long fissure-based "curtain of fire" on 3 January. These gave way to centralized eruptions on the site of Kilauea's east rift, eventually building up the still active cone.[4]
- For a list of all of the volcanoes of Hawaii, see List of volcanoes in the Hawaiian - Emperor seamount chain.
- Mount Etna, Italy.[4]
- Mount Mihara in 1986 (see above paragraph)[4]
Strombolian
Main article: Strombolian eruption
Diagram of a Strombolian eruption. (key: 1. Ash plume 2. Lapilli 3. Volcanic ash rain 4. Lava fountain 5. Volcanic bomb 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Dike 10. Magma conduit 11. Magma chamber 12. Sill) Click for larger version.
The term "Strombolian" has been used indiscriminately to describe a wide variety of volcanic eruptions, varying from small volcanic blasts to large eruptive columns. In reality, true Strombolian eruptions are characterized by short-lived and explosive eruptions of lavas with intermediate viscosity, often ejected high into the air. Columns can measure hundreds of meters in height. The lavas formed by Strombolian eruptions are a form of relatively viscous basaltic lava, and its end product is mostly scoria.[12] 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.[14]
An example of the lava arcs formed during Strombolian activity. This image is of Stromboli itself.
Strombolian eruptions are similar to Hawaiian eruptions, but there are differences. Strombolian eruptions are noisier, produce no sustained eruptive columns, do not produce some volcanic products associated with Hawaiian volcanism (specifically Pele's tears and Pele's hair), and produce fewer molten lava flows (although the eruptive material does tend to form small rivulets).[12][14]
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 424 m (1,391 ft). This was the first time that scientists are able to observe the complete life cycle of a volcano.[12]
- Mount Etna, Italy, which has displayed Strombolian activity in recent eruptions, for example in 1981, 1999,[15] 2002-2003, and 2009.[16]
- Mount Erebus in Antarctica, the southernmost active volcano in the world, having been observed erupting since 1972.[17] Eruptive activity at Erebus consists of frequent Strombolian activity.[18]
- 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.[19]
Vulcanian
Main article: Vulcanian eruption
Diagram of a Vulcanian eruption. (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.
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