Volcanic Eruptions Types

Volcanic eruptions occur when gas-rich magma rises through Earth’s crust and the internal pressure exceeds the strength of overlying rock. This causes the release of magma, volcanic gases, ash, and fragmented rock through a vent or fissure.

Eruptions can range from small, localized events to massive explosions with global impacts. Their style and intensity depend on factors such as magma composition, viscosity, gas content, depth of the magma chamber, and the presence of water. As a core process in Earth’s geologic cycle, volcanic eruptions build landforms, form igneous rocks, and can influence climate patterns.

Volcanic eruption types: Hawaiian (fluid lava), Strombolian (explosive bursts), Vulcanian (ash-heavy), Plinian (cataclysmic column), Pelean (pyroclastic flows), and Icelandic (fissure-fed).

Eruption Mechanisms

Volcanic eruptions can be categorized based on the mechanisms that drive them. These mechanisms are primarily influenced by the behavior of magma, the presence of volatiles (gases), and interactions with external water sources. The three main types of eruption mechanisms are magmatic, phreatic, and phreatomagmatic.

Magmatic eruptions

Magmatic eruptions are driven by the exsolution, or release, of dissolved gases such as water vapor (H₂O), carbon dioxide (CO₂), and sulfur dioxide (SO₂) from ascending magma. As the magma rises through the crust, the surrounding pressure decreases, allowing these volatiles to come out of solution and expand. This gas expansion propels magma toward the surface, resulting in either effusive lava flows or explosive eruptions, depending on the magma’s viscosity and gas content. Low-viscosity basaltic magmas tend to produce gentle lava flows, while high-viscosity andesitic or rhyolitic magmas are more prone to explosive fragmentation.

Phreatic (steam-driven) eruptions

Phreatic eruptions, also known as steam-driven eruptions, occur when hot magma or even just heated rock comes into contact with groundwater or surface water. The sudden temperature increase causes the water to flash into steam, leading to a violent expansion that blasts apart the surrounding rock. These eruptions are typically non-magmatic, meaning they do not involve fresh magma reaching the surface. Instead, they fragment pre-existing rock and often produce ash, steam, and volcanic gases. Because they do not involve magma directly, phreatic eruptions can be sudden and difficult to predict.

Phreatomagmatic eruptions

Phreatomagmatic eruptions represent a hybrid mechanism, involving direct interaction between rising magma and external water sources such as lakes, groundwater, or seawater. This interaction leads to intense fragmentation of the magma and explosive release of steam and gases. Phreatomagmatic eruptions are highly explosive and produce fine volcanic ash, base surges, and tuff rings. A well-known example is the Surtseyan eruption, named after the island of Surtsey, which emerged from the sea during a 1963 eruption off the coast of Iceland.

Factors Affecting the Type of Eruption

The type of volcanic eruption that occurs depends on a number of factors, including the composition of the magma, the depth of the magma chamber, and the presence of water.

Magma composition: The composition of the magma, specifically the gas content, is one of the most important factors that determines the type of eruption. Magma that is high in gas content is more likely to produce an explosive eruption.
Depth of the magma chamber: The depth of the magma chamber also plays a role in determining the type of eruption. Magma that is deep underground is also more likely to produce an explosive eruption, as the pressure builds up as the magma rises.
Presence of water: The presence of water can also trigger an explosive eruption, as the water vaporizes and expands when it comes into contact with hot magma.

There are two main types of volcanic eruptions: effusive and explosive. Effusive eruptions are characterized by the outpouring of lava without significant explosive activity. Explosive eruptions, on the other hand, are characterized by the gas-driven explosions of magma and tephra.

Types of Volcanic Eruptions

Volcanic eruptions are a natural and powerful force of nature. They can range in size from small, localized events to massive explosions that can have global consequences. The type of volcanic eruption that occurs depends on a number of factors, including the composition of the magma, the depth of the magma chamber, and the presence of water.

Effusive Eruption

Effusive eruptions are the most common type of volcanic eruption. They are typically characterized by the outpouring of lava that flows down the sides of the volcano. Lava flows can be very fluid or very viscous, depending on the composition of the magma.

Some of the most famous effusive volcanoes include Kilauea in Hawaii and Etna in Italy. These volcanoes are known for their long-term eruptions that produce large amounts of lava.

Explosive Eruption

Explosive eruptions are less common than effusive eruptions, but they can be much more violent. They are characterized by the gas-driven explosions of magma and tephra. The tephra can be carried high into the atmosphere, where it can fall as ash or pumice.

Some of the most famous explosive volcanoes include Mount Vesuvius in Italy and Krakatoa in Indonesia. These volcanoes have been responsible for some of the most destructive volcanic eruptions in history.

Types of Volcanic Eruptions

Types of Explosive Eruptions

There are several different types of explosive eruptions, each with its own characteristic features. These include:

Plinian Eruption

Plinian eruptions are a type of highly explosive eruption that generates an immense vertical eruption column.

Plinian eruptions, also sometimes called Vesuvian eruptions, are some of the most violent and awe-inspiring volcanic events. They are named after Pliny the Younger, a Roman historian who witnessed and documented the infamous eruption of Mount Vesuvius in 79 AD, which is considered a classic example of a Plinian eruption.

Plinian eruptions are characterized by their extreme explosiveness. They are driven by the forceful ejection of a huge amount of gas-rich, viscous magma into the atmosphere. This magma is often felsic or andesitic, meaning it has a high silica content, making it thicker and more prone to trapping gas bubbles.

The trapped gases violently expand as the magma fragments and rises through the vent. This propels a massive column of ash and hot gas, reaching tens of kilometers (up to 45 km) into the stratosphere, the Earth's second atmospheric layer.

The fallout from these eruptions can have devastating consequences for the surrounding environment and communities.

Strombolian Eruption

Strombolian eruptions are characterized by frequent and moderate explosions that propel lava fragments and volcanic gases into the air. These eruptions often create incandescent lava fountains and are named after the volcanic island of Stromboli in Italy, known for its regular and mesmerizing explosions. Although Strombolian eruptions are not as destructive as Plinian eruptions, they can still pose risks to nearby populations and infrastructure.

Icelandic Eruption

Icelandic eruptions are the least explosive type of eruption. They are characterized by the emission of low-viscosity lava that flows easily. Icelandic eruptions are often accompanied by lava fountains, which are tall jets of lava that shoot into the air.

Surtseyan Eruption

These rare eruptions occur underwater or in shallow coastal areas, creating explosive steam-driven events that can build new islands.

Surtseyan eruptions are a dramatic type of volcanic eruption that occurs when hot, rising magma meets shallow seawater or lakes. The sudden contact between the intensely hot magma (often exceeding 1,170°C or 2,138°F) and the water creates a violent explosion of steam, ash, and rock fragments. These eruptions are named after Surtsey, an island near Iceland that was created by a Surtseyan eruption in 1963.

Vulcanian Eruption

Vulcanian eruptions are intermediate in explosivity between Strombolian and Plinian eruptions. They involve the ejection of dense ash clouds, pyroclastic flows, and relatively small but powerful explosions. Vulcanian eruptions can be highly hazardous, as they generate fast-moving, superheated flows of gas, ash, and rocks, known as pyroclastic flows. The 1883 eruption of Krakatoa in Indonesia is a well-known example of a Vulcanian eruption.

Pelean eruptions

These are the most explosive type of eruption. They are characterized by the emission of large amounts of ash, pumice, and gas. The explosions can be very violent, and they can produce pyroclastic flows, which are hot, fast-moving currents of gas and ash that can travel great distances.

Hawaiian eruption

Hawaiian eruptions are a type of volcanic eruption characterized by relatively gentle, low-level outflows of lava. These eruptions are fueled by basaltic magmas, which are low in gas viscosity and high in temperature. This combination allows the lava to flow easily, creating vast, broad volcanoes known as shield volcanoes. The Hawaiian Islands are a prime example of a volcanic chain formed by Hawaiian eruptions.

Phreatomagmatic eruptions

Phreatomagmatic eruptions occur when magma comes into contact with water, either from a lake, ocean, or groundwater. The sudden vaporization of the water leads to explosive fragmentation of the magma, creating a mixture of volcanic ash, steam, and gases. These eruptions can be particularly dangerous as they can produce tall eruption columns and trigger devastating tsunamis. The 1963 eruption of Mount Agung in Bali, Indonesia, is an example of a phreatomagmatic eruption. The interaction between water and magma makes these eruptions highly dangerous and can produce volcanic ash clouds and lahars (mudflows).

Submarine Eruption

Submarine eruptions take place beneath the ocean's surface and are often associated with tectonic plate boundaries and volcanic hotspots. These eruptions can be effusive or explosive, and they are responsible for creating new seafloor formations and even underwater volcanoes.

Hydrothermal Eruption

Hydrothermal eruptions are caused by the circulation of hot water and steam through the Earth's crust.

Hydrothermal eruptions are a forceful event caused by superheated water flashing rapidly into steam beneath the Earth's surface. Unlike volcanic eruptions, hydrothermal eruptions don't directly involve magma interacting with the surface.

The Cause:

Superheated Water: Deep underground, water becomes heated by hot rock or magma chambers. This water can reach temperatures exceeding 250°C (482°F).
Pressure Keeps it Liquid: Normally, water boils at 100°C (212°F) at sea level. However, increased pressure raises the boiling point.
Sudden Pressure Release: When the pressure on the superheated water is released, it rapidly boils and transforms into steam, causing a violent explosion.

Illustration of the basic process of magma formation, movement to the surface, and eruption through a volcanic vent. USGS illustration.

The Effects of Volcanic Eruptions

Volcanic eruptions can have a significant impact on the surrounding environment. They can cause widespread damage to property and infrastructure, and they can also pollute the air and water. In some cases, volcanic eruptions can even cause death.

The effects of volcanic eruptions can vary depending on the type of eruption, the location of the volcano, and the prevailing weather conditions. However, some of the most common effects of volcanic eruptions include:

Lava flows: Lava flows can destroy property and infrastructure, and they can also block roads and railways.
Ashfall: Ashfall can pollute the air and water, and it can also damage crops and livestock.
Pyroclastic flows: Pyroclastic flows can travel at high speeds and can cause widespread damage.
Tsunamis: Volcanic eruptions can sometimes trigger tsunamis, which can cause widespread damage along coastal areas.

Mitigation of Volcanic Eruptions

Volcanic eruptions are a natural hazard, but they can be mitigated by careful monitoring and planning. Volcanologists can monitor volcanoes for signs of activity, and they can issue warnings to people who live in the area. Governments can also develop plans for evacuating people and responding to volcanic eruptions.

By understanding the different types of volcanic eruptions and the factors that can trigger them, we can better prepare for and mitigate the impacts of volcanic eruptions.