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What are the Types of Volcanic Eruptions?

Updated on August 9, 2012

What Types of Eruptions are There?

Volcanic eruptions are not associated with just one type of eruption, but to different types of eruptions, each produced by a distinct mechanism and varying in strength and intensity. Some volcanoes may exhibit only one eruptive characteristic, whereas others may exhibit a variety of eruptive types throughout the course of an eruption. The varied types of volcanic eruptions that are produced are often named after notable volcanologists or well-known volcanoes where a given eruptive characteristic was observed.

Eruptions are classified into three distinct eruptive types, including magmatic eruptions, involving the explosive eruptions due to gas release; phreatomagmatic eruptions driven by the compression of gases contained in magma; and phreatic eruptions caused by superheated steam as it comes in contact with magma. Within these eruptive distinctions, there are a number of subtypes, each of which gets its name from the volcano in which they occurred or the famous character which witnessed its eruption.

Highly Liquid Lava

Hawaiian Eruption
Hawaiian Eruption | Source

Hawaiian Eruptions

Hawaiian eruptions are the weakest of all types of eruptions, and are characterized by effusive ejection of highly liquid basalt lava with a minimum of gas contents. Hawaiian eruptions are not limited to a central vent, but can occur along fissure vents that spread out from the central vent. When a Hawaiian eruption starts at a fissure vent, it forms a line of eruptions known as a curtain of fire; however, the curtain tends to die down when lava begins to concentrate at a few vents. Central eruptions, on the other part, usually create lava fountains. Hawaiian eruptions are characteristic of Hawaii, hence their name.

Hawaiian eruption types often extend for long periods of time. Kilauea volcano has been outpouring lava continuously since 1983, making it the longest eruption in the last two centuries. Hawaiian eruptions are often accompanied by two types of lava. Pahoehoe lava forms fluid lava flows that look like long and thick strands of rope, and move as one single sheet of lava or as a twisting lava column. A’a lava is more viscous, and moves slower. Its outer surface forms a thick hard layer, preventing the interior lava from cooling, and as it moves, it breaks into large pieces or blocks. Hawaiian eruptions are not confined to Hawaii. They also occur in other parts of the world.

Explosive Eruptions

Strombolian Eruption
Strombolian Eruption | Source

Strombolian Eruptions

The term “Strombolian” refers to a type of volcanic eruptions characterized by brief, episodic and explosive eruptions accompanied by distinctive strenuous blasts of intermediate viscosity lava often ejected high into the air. Strombolian eruptions can be particularly impressive during dark, as lava tends to glow brightly. The term strombolian has been utilized to describe various eruption types, varying from minor and volcanic explosions to huge volcanic columns. This type of eruption is named after the volcano Stromboli, which is an island laying off the north coast of Sicily, Italy.

The lavas involved in strombolian eruptions are composed of intermediate viscosity basaltic lava. Stromboli eruptions are driven by the decompression of gases occurring within the magma. Gas bubbles accumulate and combine into larger bubbles. Once in the surface, these gas bubbles are driven out of the magma, and at the contact with surface air, they explode, reaching heights of hundreds of meters. The explosions occur at intervals of a few minutes within one another, and are accompanied by distinct loud detonations. The exploded fragments (tephra) follow parabolic paths before being deposited around their source vent. A classic example of this type of eruption is the one observed in Paricutin, Mexico.

Small Columns of Ash, Gas and pyroclastic flows

Vulcanian Eruption
Vulcanian Eruption | Source

Vulcanian Eruptions

Vulcanian eruptions are small, although, violent explosions of high content viscous lava (andesitic, dacitic) which can produce columns of gas, ash and pyroclastic flows that can reach speeds of up to 350 meters/s (984 feet/s) and rise from between 5-10 km (3-6 miles) up in the sky. In this type of eruptions, magma with high viscosity content traps gases within, causing the buildup of gas pressure. When the pressure has built up enough, it explodes, rupturing the plug of lava which is obstructing the volcanic conduit. As the lava dome wears down, eruptions become more constant and noiseless.

Vulcanian activity comprises brief series of volcanic explosions, varying from minutes to hours and characterized by the ejection of solid volcanic artifacts known as bombs and blocks. These explosions eventually erode the lava dome which results in less noisy, although, continuous eruptions. The collapse of the dome produces an outburst of pyroclastic matter down the slope of the volcano. Vulcanian eruptions owe their name to Vulcano, a small island in the north of Sicily in Italy where this type of eruption was first observed by Giuseppe Mercalli, an Italian volcanologist.

Mt. Pelée

Mt. Pelee july 16, 1902
Mt. Pelee july 16, 1902 | Source

Peléan Eruptions

Peléan eruptions are large eruptive columns of gas, dust and ash ejected out from a volcano’s crater, creating eruption columns of up to 40 km (25 miles) high. Eruption columns form when high concentration of gases in magma causes it to decompress into fine volcanic ash, which is driven high into the sky by convection currents at speeds of several hundred meters per second. A lava spine, which is a vertical monolith of viscous lava bulging out of the volcano’s top, usually precedes the onset of a Peléan eruption. When the dome of the volcano collapses, a fast moving pyroclastic flow is formed, displacing itself by the slopes and valleys of the volcano at speeds of up to 150 km/h (93 miles/h).

Before the onset of a Pelé an eruption, the structure of a volcano is able to resist stored pressure, resulting in a larger rather than small explosion. The collapse of the dome produces huge columns of volcanic ash. The dense column of ash is too dense to travel by convection high into the sky, and descends down the side of the volcano, giving rise to a pyroclastic flow. Pelean eruptions take their name after a volcano known as Mt. Pelé in the island of Martinique whose eruption in 1992 is considered as one of the worst natural disasters ever.

Volcanic Column of Ash and Gas

Plinian Eruption Mt. Redoubted
Plinian Eruption Mt. Redoubted | Source

Plinian Eruptions

Plinian eruptions, which are the most powerful type of eruption, are highly explosive eruptions caused by the decompression of very highly viscous magma, creating volcanic columns of gas and ash which can rise high up in the sky more than 50 km (35 miles) at speeds of 100 m/s (328 ft./s). As magma rises through the magma conduit, gases expand, and when they reach a size three quarters that of the magma conduit, they explode out and up through the narrow borders of the central vent. Once out, an eruptive column of hot volcanic ash and thicker tephra is formed. The eruptive column can reach heights of up to 45 km (28 miles) into the sky. The flared conduit formed from the eruption allows the gases to reach tremendous speeds.

The densest part of the column lies directly above the volcano, and as it expands higher above in the sky, it becomes denser; however, by convection and thermal expansion, ash is driven even further above. At the very top of the column, existing winds carry the plume away from the volcano. The ejected material eventually lands down on the landscape, covering it with a thick layer of ash. Pyroclastic flows created move down the slopes, reaching speeds of more than 700 km/h (435 miles/h), and ice deposits are melted by the heat, creating fast moving mudslides and lahars. Plinian eruptions, also known as Vesuvian eruptions, derive their name from Pliny the Younger, the person who chronicled the eruption of Mt Vesuvius.

Rising Magma Turns Water into Steam

Surtseyan Eruption
Surtseyan Eruption | Source

Surtseyan Eruptions

Surtseyan eruptions are highly explosive volcanic events, occurring most commonly in shallow waters of oceanic islands; however, they can also occur on land when the rising magma encounters an aquifer on its way. Most commonly, Surtseyan eruptions occur when an undersea volcano has accrued enough volcanic matter to reach the water surface. During a Surtseyan eruption, erupting lava turns water into steam which expands violently, and as it does, magma is fragmented into fine-grained ash. A turbulent mass of rock fragments and gas usually develops radially along with the eruption column.

Surtseyan eruptions, also known as hydrovolcanic eruptions, occur when lava interacts explosively with water. When lava and water come into contact, steam is produced, and as it does, it expands explosively, creating plumes of ash and scoria, which produce a cone. Eventually, this cone will grow big enough to create an island. Once the island is formed, Surtseyan eruptions become less explosive, resembling those of strombolian nature. Lavas created by Surtseyan eruptions produce basaltic lava like that of most oceanic volcanoes. Surtseyan eruptions got their name after the eruption that formed the island of Surtsey which erupted off the coast of Iceland in 1963.

Submarine Lava Flows

Submarine Eruption
Submarine Eruption | Source

Submarine Eruptions

Submarine lava flows are characterized by incremental extrusion of portions of mantle rock that are rapidly cooled when coming in contact with cold ocean water, forming pillow lava. Most pillows vary in size from 20-100 cm (8-40 inches) in diameter. Basaltic lavas form thick outer layers as soon as they’re cooled; however, the inside of pillow lavas forms a coarser crystalline structure. Submarine eruptions are natural events that occur underwater and produce seamounts which may reach the ocean’s surface to create volcanic islands

An estimated 75% of volcanic eruptions occur in the ocean floor near mid-ocean ridges and hotspots; however, they have remained undetected due to difficulty they pose at monitoring submarine eruptions. It was not until the 1990s that modern advances in technology made it possible to study them. It is believed that an approximate number of 100,000 marine volcanoes exist around the world, although most of them have surpassed the active stage of their eruptive activity. This type of volcanoes owe their name to the nature of their occurrence.

Steep-sided Volcano Known as "Tuya"

Subglacial Eruption
Subglacial Eruption | Source

Subglacial Eruptions

Subglacial eruptions are produced by the interaction between lava and ice. Subglacial volcanoes most commonly affect their ice caps by geothermal heating, producing melted water. In this way, water and heat interaction often produce dangerous glacial outpouring floods and lahars. Subglacial eruptions usually create a mountain with a flat top which consists of layers of basaltic lava covered by hyaloclastite breccia, tuff, and capped off by lava flow.

Subglacial eruptions produce a subglacial volcano referred to as tuya, also known as Table Mountain which is characterized by a flat top developed at its summit. A tuya is formed when lava finds its way through an ice sheet or glacier, and usually forms horizontal layers of basaltic lava flows that rise in isolation above a surrounding plateau. Normally subglacial eruptions produce hyaloclastite and pillow lava. Tuyas are rare around the world, and are only found, where glaciers once covered active volcanic regions, most commonly at high latitude locations of the world.

Major Volcanic Eruptions of the Last Decade

Papua New Guinea
Sangihe Islands, Indonesia
Papua New Guinea
Papua New Guinea
Mt. Okmok
Aleutian Islands of Alaska, U.S.
Aleutian Islands of Alaska, U.S.
Marine eruption at Tonga
Sarychev Peak
Mt. Merapi
Puyehue-Cordón Caulle
Mt. Etna

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