8.1 Types of volcanoes: shield, stratovolcanoes, and cinder cones
5 min read•august 16, 2024
Volcanoes come in various shapes and sizes, each with unique characteristics. Shield volcanoes, stratovolcanoes, and cinder cones differ in their formation, structure, and eruption patterns. These differences stem from the type of magma that forms them.
Understanding volcano types is crucial for predicting eruptions and assessing hazards. Shield volcanoes produce fluid lava flows, while stratovolcanoes can unleash explosive eruptions. Cinder cones, though smaller, can form quickly and disrupt local areas.
Volcano Types: Characteristics and Formation
Morphological Features and Size
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- Shield volcanoes have broad, gently sloping profiles resembling a warrior's shield with slopes typically less than 10 degrees
- Stratovolcanoes (composite volcanoes) feature steep, conical shapes with slopes often exceeding 30 degrees
- Cinder cones are small, steep-sided volcanic structures typically less than 300 meters tall
- Shield volcanoes cover hundreds of square kilometers while cinder cones are the smallest and most common type
- Stratovolcanoes compose of alternating layers of lava, ash, and other volcanic debris
- Cinder cones consist primarily of loose pyroclastic fragments (cinders or scoria)
Internal Structure and Eruption Patterns
- Shield volcanoes contain extensive systems facilitating distribution
- Stratovolcanoes possess complex networks of dikes and sills within their structure
- Cinder cones lack significant internal structures due to their simple formation process
- Shield volcanoes often experience long-lived, less explosive eruptions
- Stratovolcanoes exhibit both effusive and explosive eruptions
- Cinder cones typically form in single, short-lived eruption events
- Parasitic cones and flank eruptions commonly occur on larger shield volcanoes and stratovolcanoes
Post-Formation Processes and Features
- Erosional processes affect each volcano type differently
- Stratovolcanoes often develop deep gullies and canyons due to their composition
- Shield volcanoes resist erosion more effectively because of their basaltic composition
- size and shape vary among volcano types
- Shield volcanoes often have large, shallow calderas
- Stratovolcanoes potentially develop smaller, deeper calderas
- Cinder cones typically feature a bowl-shaped crater at the summit
Magma Composition and Volcano Type
Silica Content and Viscosity
- Magma composition, particularly silica content and , primarily determines volcano type and eruptive style
- Shield volcanoes associate with low-viscosity, low-silica basaltic magmas (45-52% silica)
- Stratovolcanoes form from intermediate to felsic magmas
- Andesitic magmas: 52-65% silica
- Rhyolitic magmas: over 65% silica
- Cinder cones typically associate with basaltic to basaltic-andesitic magmas (45-57% silica)
- Low-silica magmas allow for fluid lava flows and gentle slopes (shield volcanoes)
- High-silica magmas result in more viscous lavas and explosive eruptions (stratovolcanoes)
Gas Content and Temperature
- in magma influences eruption explosivity
- Higher gas content in silica-rich magmas contributes to explosive eruptions
- Magma temperature correlates with composition, affecting viscosity and eruptive behavior
- Basaltic magmas: 1000-1200°C
- Rhyolitic magmas: 700-850°C
- Hotter magmas generally have lower viscosity, promoting more fluid lava flows
Magma Evolution and Differentiation
- Magma evolution and differentiation processes can alter composition over time
- Changes in magma composition potentially modify eruptive style and volcano morphology
- Fractional crystallization and assimilation of crustal rocks contribute to magma evolution
- Magma mixing in volcanic plumbing systems can result in hybrid compositions
Volcano Morphology and Eruptive Behavior
Shield Volcano Characteristics
- Shield volcanoes exhibit effusive eruptions characterized by lava fountains and extensive lava flows
- Form features such as lava tubes, rift zones, and summit calderas
- Lava tubes efficiently transport lava over long distances, contributing to the volcano's broad shape
- Rift zones represent areas of weakness where fissure eruptions commonly occur
- Summit calderas form through repeated collapse events or sustained lava lake activity
Stratovolcano Dynamics
- Stratovolcanoes display complex eruptive behavior, alternating between effusive and explosive eruptions
- Create layered deposits from varied eruption styles
- Form features like lava domes, pyroclastic flows, and lahars
- Lava domes result from viscous lava accumulating over the
- Pyroclastic flows consist of hot gas, ash, and rock fragments traveling at high speeds
- Lahars are volcanic mudflows that can occur during eruptions or from rainfall on loose volcanic deposits
Cinder Cone Formation
- Cinder cones form through Strombolian eruptions
- Eject tephra that accumulates around a central vent
- Often feature a bowl-shaped crater at the summit
- Occasional lava flows may emerge from the base of the cone
- Tephra accumulation creates steep slopes near the angle of repose
Slope Angles and Lava Viscosity
- Slope angle of each volcano type directly relates to the viscosity of its typical lava flows
- Shield volcanoes have the lowest slopes due to low-viscosity basaltic lavas
- Stratovolcanoes have the steepest slopes resulting from more viscous intermediate to felsic lavas
- Cinder cones have steep slopes due to the accumulation of loose pyroclastic material
Volcano Hazards: A Comparative Analysis
Shield Volcano Hazards
- Shield volcanoes primarily pose hazards through lava flows
- Can cover large areas but generally move slowly enough for evacuation
- Potential ground deformation affecting infrastructure
- Gas emissions may cause localized air quality issues
- Lava deltas formed at coastlines can collapse, creating localized tsunami hazards
Stratovolcano Hazards
- Stratovolcanoes present the widest range of hazards
- Pyroclastic flows: fast-moving currents of hot gas, ash, and rock fragments
- Lahars: volcanic mudflows that can travel long distances along river valleys
- Ash falls: can affect large areas, damaging crops and infrastructure
- Lateral blasts: directed explosions that can devastate areas in a specific direction
- Sector collapse: large-scale landslides that can trigger debris avalanches
- Volcanic earthquakes and ground deformation more pronounced than in other volcano types
Cinder Cone Hazards
- Cinder cones typically pose localized hazards
- : rocks and cinders thrown from the vent
- Small-scale lava flows: generally limited in extent
- Ash falls: usually affect only the immediate vicinity of the cone
- Impacts generally limited to the immediate vicinity of the cone
Common Hazards Across Volcano Types
- Gas emissions pose risks to human and animal health
- Potential pollution of water sources from volcanic activity
- Long-term environmental and climatic impacts differ among volcano types
- Large stratovolcanic eruptions potentially cause global climate effects through stratospheric aerosol injection
- Volcanic smog (vog) can affect air quality over large areas, particularly for shield volcanoes with persistent degassing
Key Terms to Review (28)
Andesitic magma: Andesitic magma is a type of intermediate volcanic rock that has a higher silica content than basaltic magma but lower than rhyolitic magma. It typically forms at convergent plate boundaries, where oceanic plates subduct beneath continental plates, leading to the melting of mantle materials and the formation of this specific magma type. The characteristics of andesitic magma result in explosive eruptions, primarily associated with stratovolcanoes.
Ash fall: Ash fall refers to the deposition of volcanic ash, a fine particulate material ejected during explosive volcanic eruptions, onto the Earth's surface. This phenomenon can significantly impact both the environment and human activities, as the accumulation of ash can blanket large areas, affecting air quality, agriculture, and infrastructure. Ash fall is commonly associated with stratovolcanoes but can occur from various types of volcanic eruptions, making it crucial to understand its relationship with different volcano forms and tectonic settings.
Ballistic ejecta: Ballistic ejecta refers to volcanic materials that are expelled from a volcano during an explosive eruption, often traveling through the air in a ballistic trajectory. This ejected material can include a variety of particles such as ash, volcanic rocks, and pyroclastic fragments, which are propelled outward due to the force of the eruption. The nature and size of ballistic ejecta can vary greatly, depending on the type of volcano and the characteristics of the eruption itself.
Basaltic magma: Basaltic magma is a type of molten rock that is low in viscosity and contains a high proportion of iron and magnesium, resulting in its dark color and high temperature. This type of magma is primarily associated with divergent plate boundaries and hotspots, playing a crucial role in forming specific types of volcanoes characterized by their shape and eruption style.
Caldera: A caldera is a large depression formed when a volcano erupts and collapses after the magma chamber is emptied. This geological feature can be several kilometers in diameter and may contain a lake or be filled with volcanic debris. Calderas often represent the end stage of volcanic activity and can be associated with different types of volcanoes, as well as with hotspot activity.
Cinder Cone: A cinder cone is a type of volcano characterized by its steep, conical shape formed from the accumulation of volcanic debris, primarily small fragments of lava called cinders. These volcanoes are typically built from explosive eruptions that eject ash and rock fragments high into the air, which then fall back around the vent, creating the cone-like structure. Cinder cones are generally the smallest and simplest type of volcano, often found on the flanks of larger volcanoes or in volcanic fields.
Effusive Eruption: An effusive eruption is a volcanic event characterized by the relatively gentle flow of lava onto the Earth's surface, resulting in the formation of features such as lava plateaus and shield volcanoes. This type of eruption occurs when magma is low in viscosity, allowing it to flow easily and spread over large areas. In contrast to explosive eruptions, effusive eruptions produce less ash and gas, leading to a different set of volcanic products and landforms.
Evacuation Plans: Evacuation plans are organized strategies designed to guide individuals in safely leaving a potentially dangerous area, particularly in response to natural disasters like volcanic eruptions. These plans detail routes, shelters, communication protocols, and responsibilities, ensuring that people can efficiently and effectively respond to emergencies. Understanding these plans is crucial when dealing with geological hazards, as they help mitigate risks associated with volcanic activity and other environmental threats.
Explosive eruption: An explosive eruption is a volcanic event characterized by the violent expulsion of magma, gas, and ash into the atmosphere, resulting in a significant release of energy. This type of eruption often occurs in stratovolcanoes, where the viscosity of the magma traps gases until pressure builds up to critical levels. Explosive eruptions can produce various volcanic products, including pyroclastic flows, ash falls, and volcanic gases, which have a profound impact on the surrounding environment and climate.
Gas content: Gas content refers to the amount and types of gases dissolved in magma before it erupts. The gas content is a crucial factor that influences the explosiveness of a volcanic eruption, determining how magma behaves as it rises to the surface. High gas content can lead to more explosive eruptions, while low gas content typically results in more gentle outpourings of lava.
Hotspot: A hotspot is a location on the Earth's surface that has experienced volcanic activity due to a mantle plume, which is a rising column of hot magma from deep within the mantle. Hotspots can occur far from tectonic plate boundaries and lead to the formation of unique types of volcanoes, including shield volcanoes, stratovolcanoes, and cinder cones. These volcanic features are formed by the consistent upwelling of magma that breaks through the crust over time, creating distinct geological formations.
Lahar: A lahar is a type of destructive mudflow or debris flow that originates from volcanic activity, often triggered by heavy rainfall or the melting of snow and ice on a volcano. These flows can carry volcanic ash, rock fragments, and water, resulting in a fast-moving and highly destructive force. Lahars are especially associated with stratovolcanoes due to their steep slopes and the potential for explosive eruptions that can destabilize surrounding material.
Lava dome: A lava dome is a steep, dome-shaped mound formed by the slow extrusion of viscous lava from a volcano. These structures are typically created by the accumulation of lava that piles up near the vent, leading to a characteristic bulbous appearance. Lava domes can vary in size and shape and are often associated with explosive eruptions due to the buildup of pressure beneath the surface.
Lava flow: A lava flow is a stream of molten rock that erupts from a volcano and moves down its slopes or across the ground. The characteristics of lava flows, such as their speed, temperature, and composition, are influenced by the type of volcano they originate from, which can determine whether they form broad, gentle slopes or steep, conical shapes.
Lava tube: A lava tube is a natural conduit formed by flowing lava that moves beneath the surface of a lava flow. These tubes can transport molten rock over considerable distances and often remain intact after the lava has drained away, resulting in hollow tunnels. Lava tubes are significant because they can provide insights into volcanic activity and contribute to the formation of various types of volcanoes, including shield volcanoes, stratovolcanoes, and cinder cones, as well as influencing the products of volcanic eruptions.
Magma formation: Magma formation refers to the process by which molten rock is generated beneath the Earth's surface, primarily through the melting of rocks in the mantle or crust. This process is influenced by temperature, pressure, and the composition of the rocks involved, resulting in different types of magma that can lead to various volcanic eruptions and landforms. Understanding magma formation is essential for connecting the characteristics of different volcanoes and how they relate to tectonic plate boundaries.
Plate Boundary: A plate boundary is the region where two tectonic plates meet, and it plays a critical role in shaping the Earth's surface through various geological processes. These boundaries are classified into three main types: divergent, convergent, and transform, each associated with distinct geological features and activities, such as earthquakes and volcanic activity. The interaction at these boundaries can lead to the formation of different types of volcanoes, fault systems, and the dynamic nature of Earth’s internal structure.
Plinian eruption: A Plinian eruption is a type of explosive volcanic eruption characterized by the violent expulsion of ash, pumice, and gases high into the atmosphere. These eruptions are named after Pliny the Younger, who documented the eruption of Mount Vesuvius in 79 AD. The immense columns of volcanic material can reach altitudes of 30 kilometers or more, significantly impacting the environment and climate. Plinian eruptions primarily occur at stratovolcanoes, where thick, viscous magma traps gas until it is released violently, leading to the formation of expansive ash deposits and pyroclastic flows.
Pyroclastic flow: A pyroclastic flow is a fast-moving current of hot gas, ash, and volcanic rock that erupts from a volcano during explosive eruptions. These flows can travel at incredible speeds, often exceeding 100 km/h (62 mph), and can reach temperatures of about 1,000°C (1,832°F). Due to their high density and speed, pyroclastic flows pose a significant hazard to life and property in the vicinity of active volcanoes, particularly in relation to different types of volcanoes and their eruptive styles as well as the tectonic processes that create these volcanic systems.
Rhyolitic magma: Rhyolitic magma is a type of molten rock that is high in silica content and is typically associated with explosive volcanic eruptions. This magma is characterized by its thick, viscous nature, which prevents gases from escaping easily, leading to pressure buildup and powerful eruptions. The composition and behavior of rhyolitic magma significantly influence the formation and eruption styles of different volcano types.
Rift zone: A rift zone is a region of the Earth's crust where tectonic plates are diverging, leading to the formation of new oceanic or continental crust. This geological feature is often characterized by volcanic activity and the creation of fissures and valleys, which can result in various types of volcanoes, including shield, stratovolcanoes, and cinder cones, due to the magma that rises to the surface as the plates separate.
Shield Volcano: A shield volcano is a type of volcano characterized by its broad, gently sloping sides, resembling a warrior's shield. These volcanoes primarily erupt low-viscosity basaltic lava that can flow over great distances, which contributes to their wide, dome-like shape. Shield volcanoes are often formed by hot spot volcanic activity, where magma from the mantle rises to the surface, creating extensive lava flows that build up the structure over time.
Stratovolcano: A stratovolcano, also known as a composite volcano, is a steep, conical volcano characterized by its layered structure formed from alternating eruptions of lava and tephra. These volcanoes are typically associated with explosive eruptions due to the viscosity of their magma, which often contains high levels of silica. Stratovolcanoes are commonly found at convergent plate boundaries, where oceanic plates subduct beneath continental plates, leading to the formation of volcanic arcs.
Subduction: Subduction is the geological process where one tectonic plate moves under another and sinks into the mantle as the plates converge. This process is crucial in shaping Earth’s features, influencing everything from the formation of oceanic trenches to the creation of mountain ranges and volcanic activity.
Tepra: Tepra refers to the volcanic ash and fragmental material that is ejected during explosive volcanic eruptions. This material can vary in size from fine dust to large blocks, and it plays a crucial role in shaping the landscape around volcanoes. The characteristics of tepra are influenced by the type of volcano it originates from, which can help determine the nature of the eruption and the potential hazards associated with it.
Vent: A vent is an opening in the Earth's surface through which magma, gases, and other volcanic materials are expelled during a volcanic eruption. Vents can vary in size and shape, and they play a crucial role in the type of volcano that forms, influencing whether it becomes a shield volcano, stratovolcano, or cinder cone based on the nature of the eruptions and the materials emitted.
Viscosity: Viscosity is a measure of a fluid's resistance to flow, which is influenced by the fluid's temperature and composition. In geological contexts, viscosity plays a critical role in determining how magma behaves during volcanic eruptions and how heat is transferred through the mantle. The differences in viscosity among various types of magma can lead to distinct volcanic formations and eruption styles.
Volcanic Monitoring: Volcanic monitoring is the systematic observation and analysis of volcanic activity to predict eruptions and mitigate hazards associated with volcanic eruptions. This process involves utilizing various techniques such as seismology, gas measurements, satellite imagery, and ground deformation studies to gather data on the behavior of different types of volcanoes, including shield volcanoes, stratovolcanoes, and cinder cones. By closely monitoring these activities, scientists can provide timely warnings to nearby communities, enhancing public safety and preparedness.