3.1 Classification of Eruption Styles
6 min read•july 30, 2024
Volcanic eruptions come in different styles, from gentle lava flows to explosive blasts. The type of eruption depends on the magma's composition and gas content. Understanding these styles helps scientists predict hazards and plan for emergencies.
Effusive eruptions produce flowing lava, while explosive ones shoot out ash and rocks. Each style poses unique risks to people and property nearby. Knowing the differences helps communities prepare for potential dangers and respond effectively when volcanoes erupt.
Volcanic Eruption Styles
Explosivity and Magma Composition
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- The explosivity of a volcanic eruption is determined by the amount of dissolved gases in the magma and how easily they can escape
- Magmas with higher gas content and more viscous compositions tend to erupt more explosively
- Magma composition, particularly silica content, influences eruption style
- Mafic magmas (basaltic) have lower silica content and lower viscosity
- Felsic magmas (rhyolitic) have higher silica content and higher viscosity
- The Volcanic Explosivity Index (VEI) is a scale used to quantify the explosiveness of volcanic eruptions, ranging from 0 (non-explosive) to 8 (highly explosive)
- The VEI is based on the volume of ejected, the height of the eruption column, and the duration of the eruption
- Examples:
- VEI 0: Kilauea, Hawaii (effusive basaltic eruptions)
- VEI 6: Mount Pinatubo, Philippines (1991 explosive rhyolitic eruption)
Magma Properties and Eruption Dynamics
- Magma viscosity plays a crucial role in determining eruption style
- Low-viscosity magmas (basaltic) allow gases to escape more easily, leading to effusive eruptions
- High-viscosity magmas (rhyolitic) trap gases, leading to pressure buildup and explosive eruptions
- Gas content and composition also influence eruption style
- Magmas with higher concentrations of dissolved water and carbon dioxide are more likely to erupt explosively
- Rapid decompression of magma can cause explosive fragmentation and the formation of ash and pumice
- Conduit geometry and magma ascent rate affect eruption dynamics
- Narrow conduits and rapid ascent rates promote explosive eruptions
- Wide conduits and slower ascent rates favor effusive eruptions
Effusive vs Explosive Eruptions
Effusive Eruptions
- Effusive eruptions are characterized by the relatively gentle and steady flow of lava onto the Earth's surface
- These eruptions typically produce lava flows, lava fountains, and lava lakes
- Examples:
- Kilauea, Hawaii: Continuous effusive eruptions with lava flows and lava lakes
- Nyiragongo, Democratic Republic of the Congo: Lava lake and intermittent lava flows
- Effusive eruptions are associated with low-viscosity, mafic magmas (basaltic)
- Low viscosity allows gases to escape easily, preventing pressure buildup
- Basaltic magmas have lower silica content and higher temperatures, promoting fluid lava flows
Explosive Eruptions
- Explosive eruptions are characterized by the violent fragmentation of magma, producing ash, pumice, and other pyroclastic materials
- These eruptions are often associated with the formation of ash plumes, pyroclastic density currents, and volcanic bombs
- Examples:
- Mount St. Helens, USA (1980): with a massive ash plume and pyroclastic density currents
- Krakatoa, Indonesia (1883): Catastrophic with widespread ash fall and tsunamis
- Explosive eruptions are associated with high-viscosity, felsic magmas (rhyolitic)
- High viscosity traps gases, leading to pressure buildup and explosive fragmentation
- Rhyolitic magmas have higher silica content and lower temperatures, promoting explosive behavior
- The transition between effusive and explosive eruption styles can occur within a single eruption or between different eruptions of the same volcano, depending on changes in magma composition, gas content, and conduit dynamics
Eruption Characteristics
Hawaiian Eruptions
- Hawaiian eruptions are effusive, characterized by the emission of fluid, basaltic lava from fissures or central vents
- They produce lava fountains, lava flows, and lava lakes
- Examples:
- Kilauea, Hawaii: Continuous effusive eruptions with lava fountains and lava flows
- Mauna Loa, Hawaii: Intermittent effusive eruptions with extensive lava flows
- Hawaiian eruptions are named after the volcanoes of Hawaii, where this style of eruption is common
- The low viscosity of basaltic magma allows for the gentle, non-explosive emission of lava
- Lava fountains can reach heights of several hundred meters, feeding lava flows and lava lakes
Strombolian Eruptions
- Strombolian eruptions are mildly explosive, characterized by the rhythmic ejection of incandescent lava fragments and ash from a central vent
- They produce short-lived lava fountains, small ash plumes, and scoria cones
- Example: Stromboli, Italy: Continuous mild explosions with ejection of lava bombs and ash
- Strombolian eruptions are named after Stromboli volcano in Italy, known for its persistent, mild explosive activity
- The intermittent bursting of gas bubbles through a semi-molten magma plug causes the ejection of lava fragments
- The explosions occur at regular intervals, ranging from seconds to minutes
Vulcanian Eruptions
- Vulcanian eruptions are moderately explosive, characterized by the periodic ejection of ash, gas, and volcanic bombs from a central vent
- They often produce ash plumes, pyroclastic density currents, and lava domes
- Example: Sakurajima, Japan: Frequent moderate explosions with ash plumes and volcanic bombs
- Vulcanian eruptions are named after Vulcano Island in Italy, where this style of eruption was first described
- The explosions are caused by the sudden release of pressurized gases trapped beneath a solidified magma plug
- The fragmentation of the magma plug produces ash, gas, and volcanic bombs that are ejected from the vent
Plinian Eruptions
- Plinian eruptions are highly explosive, characterized by the sustained emission of a high-altitude ash plume and the widespread dispersal of pumice and ash
- They can produce extensive ash fall, pyroclastic density currents, and caldera collapse
- Example: Mount Vesuvius, Italy (79 AD): Catastrophic Plinian eruption that buried the cities of Pompeii and Herculaneum
- Plinian eruptions are named after Pliny the Younger, who described the 79 AD eruption of Mount Vesuvius
- The high viscosity and gas content of felsic magmas (rhyolitic) lead to the explosive fragmentation of magma
- The sustained, high-velocity emission of ash and pumice forms a towering eruption column that can reach the stratosphere
Eruption Style and Hazards
Effusive Eruption Hazards
- Effusive eruptions primarily pose hazards associated with lava flows
- Damage to infrastructure: Lava flows can destroy buildings, roads, and other structures in their path
- Land cover changes: Lava flows can alter landscapes, burying vegetation and modifying ecosystems
- Secondary fires: The heat from lava flows can ignite vegetation and structures, causing secondary fires
- Lava flows can also interact with water, causing explosive phreatic eruptions
- When lava comes into contact with water (e.g., ocean, lakes, or groundwater), the rapid heating and vaporization of water can cause steam-driven explosions
- These explosions can produce ash plumes, ballistic projectiles, and localized tsunamis
Explosive Eruption Hazards
- Explosive eruptions pose a wide range of hazards, including ash fall, pyroclastic density currents, volcanic bombs, and lahars
- Ash fall:
- Respiratory issues: Inhalation of fine volcanic ash can cause respiratory problems and exacerbate pre-existing conditions
- Damage to infrastructure: Ash accumulation can collapse roofs, clog machinery, and disrupt electrical systems
- Disruption of transportation and communication systems: Ash can reduce visibility, damage vehicles, and interfere with satellite and radio communications
- Pyroclastic density currents:
- Fast-moving, ground-hugging flows of hot ash, pumice, and gas that can cause widespread destruction and loss of life
- Can travel at speeds up to several hundred kilometers per hour and cover vast areas
- Examples: Mount Pelée, Martinique (1902) and Mount St. Helens, USA (1980)
- Volcanic bombs:
- Large, ejected fragments that can cause impact damage and injuries in proximal areas
- Can range in size from centimeters to several meters in diameter
- Example: Galeras, Colombia (1993), where volcanic bombs injured and killed several volcanologists
- Lahars:
- Volcanic mudflows that occur when volcanic debris mixes with water from rainfall, melting snow, or crater lakes
- Can travel long distances downstream, inundating and burying areas in their path
- Example: Nevado del Ruiz, Colombia (1985), where lahars caused the destruction of Armero town and over 23,000 fatalities
- Ash fall:
Hazard Assessment and Risk Management
- The magnitude and extent of volcanic hazards are influenced by the eruption style, duration, and proximity to populated areas
- Understanding eruption styles is crucial for hazard assessment, risk management, and emergency response planning
- Hazard maps: Delineating potential impact zones for different eruption scenarios and hazards
- Risk assessment: Evaluating the likelihood and consequences of volcanic hazards on people, infrastructure, and the environment
- Early warning systems: Monitoring volcanic activity and providing timely alerts to authorities and the public
- Evacuation planning: Developing and implementing evacuation procedures and designating safe zones
- Land-use planning: Regulating development in high-risk areas and promoting sustainable land-use practices around volcanoes
Key Terms to Review (21)
Ash cloud: An ash cloud is a suspended mixture of fine volcanic ash, gas, and other volcanic materials that are ejected into the atmosphere during an explosive volcanic eruption. These clouds can rise high into the atmosphere and travel long distances, affecting air travel and air quality, as well as impacting climate patterns due to their reflective properties.
Degassing: Degassing is the process by which volcanic gases are released from magma as it ascends towards the Earth's surface, reducing the gas content in the magma and affecting eruption dynamics. This release of gas can significantly influence the style and explosiveness of eruptions, as well as impact the types of volcanic products generated during an eruption.
Effusive eruption: An effusive eruption is a volcanic event characterized by the gentle flow of low-viscosity lava, which results in the formation of broad, shield-shaped volcanoes. These eruptions are generally less explosive than other types, allowing lava to spread out over large areas, creating distinct landforms and contributing to the landscape's evolution.
Explosive eruption: An explosive eruption is a volcanic eruption characterized by the violent expulsion of magma, gas, and volcanic ash into the atmosphere. This type of eruption is typically associated with high-viscosity magma that traps gas, leading to intense pressure buildup and a sudden release, resulting in an explosive release of materials.
Gas emissions: Gas emissions are the release of gases into the atmosphere during volcanic activity, which can include water vapor, carbon dioxide, sulfur dioxide, and other volatile compounds. These emissions play a crucial role in understanding volcanic behavior, potential hazards, and their environmental impacts. The types and amounts of gases released can indicate the nature of an eruption and help to assess risks to surrounding communities.
Hawaiian-style eruptions: Hawaiian-style eruptions are characterized by relatively gentle, non-explosive lava flows that primarily emit basaltic magma. This type of eruption often results in the formation of extensive lava fountains and broad, shield-shaped volcanoes, distinguishing them from more explosive eruption styles. The low viscosity of the basaltic lava allows it to flow easily, creating large volumes of lava that can travel great distances, contributing to the gradual build-up of volcanic landforms.
Krakatoa Eruption: The Krakatoa eruption refers to a catastrophic volcanic event that occurred in 1883 on the island of Krakatoa in Indonesia, known for its violent explosion and the massive tsunamis it generated. This eruption is significant in the study of caldera systems, types of volcanic hazards, eruption styles, and has had profound global climatic effects, illustrating the interconnectedness of volcanic activity and climate change.
Lahar: A lahar is a destructive volcanic mudflow composed of a mixture of water, volcanic ash, and debris that flows down the slopes of a volcano. These flows can occur during or after an eruption, especially when heavy rainfall mobilizes volcanic materials, leading to rapid and often devastating movements of sediment.
Lava fountain: A lava fountain is a spectacular eruption phenomenon where molten rock is explosively ejected from a volcano, forming high jets or sprays of lava that can reach impressive heights. These fountains result from gas buildup in the magma that creates pressure, which, when released, propels the lava into the air. The dynamics of lava fountains play a significant role in understanding different eruption styles and assessing potential hazards associated with volcanic activity.
Magma differentiation: Magma differentiation is the process by which a single magma source evolves into different types of magma, resulting in variations in composition and physical properties. This process is influenced by factors such as temperature, pressure, and the presence of crystals that may settle out or react with the liquid magma, leading to diverse volcanic rock types.
Mount St. Helens eruption: The Mount St. Helens eruption refers to the catastrophic volcanic event that occurred on May 18, 1980, when the volcano erupted in Washington State, leading to one of the most significant natural disasters in U.S. history. This eruption resulted in explosive ash plumes, pyroclastic flows, and massive landslides, showcasing various volcanic hazards and providing critical insights into eruption styles and their impacts on society and the economy.
Plinian eruption: A Plinian eruption is a type of volcanic eruption characterized by the explosive ejection of ash, gas, and pumice into the atmosphere, producing a towering vertical column that can reach high altitudes. These eruptions are often associated with highly viscous magma, leading to significant pyroclastic flows and widespread tephra fallout, which can impact vast areas around the volcano.
Pyroclastic flow: A pyroclastic flow is a fast-moving current of hot gas and volcanic matter, such as ash and rock fragments, that flows down the slopes of a volcano during an explosive eruption. This deadly phenomenon is characterized by its high temperatures and speeds, making it one of the most hazardous volcanic phenomena.
Seismic activity: Seismic activity refers to the frequency and intensity of earthquakes and other ground vibrations caused by tectonic processes. This term is crucial in understanding how tectonic plates interact, leading to different eruption styles and volcanic activity, especially in regions with intraplate volcanism and hotspots.
Shield volcano: A shield volcano is a broad, dome-shaped volcano characterized by gentle slopes and built up primarily from the flow of low-viscosity basaltic lava. This type of volcano typically produces effusive eruptions, leading to extensive lava flows that can cover large areas, creating a shield-like profile when viewed from above.
Stratovolcano: A stratovolcano is a steep, conical volcano built up by the accumulation of lava flows, volcanic ash, and other volcanic debris. These volcanoes are characterized by their explosive eruption style and layered structure, making them prominent features in many volcanic landscapes. Their formation and eruption dynamics are crucial to understanding volcanic hazards, eruption styles, and planetary comparisons.
Strombolian eruption: A strombolian eruption is characterized by moderate explosive activity that results in the ejection of volcanic material, typically including small blobs of lava, ash, and gas, into the air at intervals. These eruptions often create a distinct rhythmic pattern and are primarily associated with basaltic magma, which allows for the formation of cinder cones and spatter cones as well as influencing the flow behavior of lava.
Tephra: Tephra refers to all the fragmented volcanic material that is ejected into the air during a volcanic eruption, which can vary in size from fine ash to large volcanic bombs. Understanding tephra is essential, as it relates to the classification of eruption styles, the types of volcanic products produced, and the formation of various volcanic landforms.
VEI Scale: The Volcanic Explosivity Index (VEI) is a logarithmic scale used to measure the explosiveness of volcanic eruptions. Ranging from 0 to 8, it helps classify eruptions based on the volume of erupted material, eruption cloud height, and qualitative observations. The VEI Scale is crucial for understanding the potential impact of eruptions, particularly when classifying different eruption styles and assessing the features associated with specific volcanic structures.
Volcanic winter: Volcanic winter refers to the significant and often prolonged cooling of Earth's climate that can occur following a large volcanic eruption. This phenomenon happens due to the injection of ash and sulfur dioxide into the stratosphere, which can reflect sunlight and reduce temperatures globally. The intensity and duration of a volcanic winter can vary based on the eruption's magnitude and the amount of particulates released into the atmosphere.
Vulcanian eruption: A vulcanian eruption is characterized by a series of explosive bursts of volcanic material, typically involving the ejection of ash, gas, and volcanic rock fragments. These eruptions are often associated with viscous magma that traps gas, leading to pressure build-up and resulting in a sudden release of energy. Vulcanian eruptions represent a significant type of explosive activity, bridging the gap between strombolian and plinian eruption styles.