Stratovolcanoes and shield volcanoes are two distinct types of volcanoes with unique shapes and behaviors. Stratovolcanoes are steep and cone-shaped, prone to explosive eruptions. Shield volcanoes are flatter and wider, known for their gentle lava flows.
The differences stem from their and eruptive styles. Stratovolcanoes have silica-rich, viscous magma that builds . Shield volcanoes have fluid, basaltic lava that spreads out, creating broad, .
Stratovolcanoes vs Shield Volcanoes
Morphology and Composition
Stratovolcanoes, also known as composite volcanoes, are characterized by their steep-sided, conical shape resulting from the buildup of viscous lava flows, ash, and tephra during eruptions
Example: in Japan, known for its nearly perfect conical shape
Shield volcanoes have a broad, gently sloping morphology resembling a warrior's shield, formed by the accumulation of fluid, low-viscosity basaltic lava flows
Example: in Hawaii, which has a diameter of about 120 km and a height of 4,169 m above sea level
The magma in stratovolcanoes is often andesitic to rhyolitic in composition, containing higher silica content and dissolved gases
Higher silica content makes the magma more viscous and prone to explosive eruptions
The magma in shield volcanoes is typically basaltic, with lower silica content and lower gas content compared to stratovolcanoes
Lower silica content results in more fluid lava that can flow easily and create the gentle slopes of shield volcanoes
Eruptive Characteristics
Stratovolcanoes typically produce explosive eruptions due to the high viscosity and gas content of their magma, which can result in pyroclastic flows, ash clouds, and lahars
Example: The 1980 eruption of in the United States, which produced a massive ash cloud and devastating pyroclastic flows
Shield volcanoes are associated with effusive eruptions, producing relatively gentle outpourings of fluid, low-viscosity basaltic lava that can travel long distances before solidifying
Example: The ongoing eruptions at in Hawaii, which have been continuously producing lava flows since 1983
The eruptive behavior of stratovolcanoes is often episodic, with periods of dormancy punctuated by violent, explosive eruptions, while shield volcanoes tend to have more continuous, steady eruptive activity
Stratovolcanoes may have centuries or even millennia between major eruptions, while shield volcanoes can have nearly continuous activity
Volcano Development Factors
Magma Properties and Tectonic Setting
Magma composition plays a crucial role in determining the type of volcano formed, with stratovolcanoes associated with more silica-rich, viscous magmas and shield volcanoes with less silica-rich, fluid magmas
Silica content affects the viscosity and gas content of the magma, influencing the eruptive style and morphology of the volcano
Tectonic setting influences volcano formation, with stratovolcanoes commonly found in zones where oceanic crust is subducted beneath continental crust, while shield volcanoes are often associated with hot spots or mid-ocean ridges
Example: The Cascade Range in the western United States, which includes several stratovolcanoes like Mount Rainier and Mount Shasta, is located along a subduction zone
Example: The Hawaiian Islands, which are home to numerous shield volcanoes, are situated over a hot spot in the middle of the Pacific Plate
Magma Supply and Volcanic System Evolution
Magma supply rate affects volcano morphology, with shield volcanoes typically having a higher and more consistent magma supply compared to stratovolcanoes
Higher magma supply rates contribute to the formation of the broad, gently sloping shield shape
Magma chamber depth and size can influence the eruptive style and frequency of volcanic activity, with shallower and smaller magma chambers often associated with more explosive eruptions in stratovolcanoes
Larger, deeper magma chambers in shield volcanoes allow for the storage and steady supply of magma to the surface
The presence of groundwater or surface water can contribute to the explosive nature of eruptions through phreatomagmatic interactions
Water coming into contact with hot magma can cause steam explosions and contribute to the formation of ash and pyroclastic material
The age and evolution of the volcanic system can impact the morphology and eruptive characteristics, with older, more mature volcanoes often exhibiting more complex structures and eruptive histories
Example: Mount Etna in Italy, which has been active for over 500,000 years, displays characteristics of both stratovolcanoes and shield volcanoes due to its complex evolution
Volcano Hazards
Stratovolcano Hazards
Stratovolcanoes pose significant hazards due to their explosive eruptions, which can generate pyroclastic flows, ash falls, and volcanic bombs that can cause destruction, burial, and incineration of surrounding areas
Example: The 79 AD eruption of in Italy buried the cities of Pompeii and Herculaneum under ash and pyroclastic flows
Pyroclastic flows are fast-moving, ground-hugging avalanches of hot ash, pumice, and volcanic gases that can travel at speeds up to 700 km/h and reach temperatures of 1,000°C
These flows can cause complete destruction and loss of life in their path
Lahars, or volcanic mudflows, are another major hazard associated with stratovolcanoes, formed by the mixing of volcanic ash, debris, and water from melting snow or heavy rainfall
Example: The 1985 eruption of Nevado del Ruiz in Colombia triggered lahars that killed over 23,000 people in the town of Armero
Shield Volcano and Other Hazards
Shield volcanoes, while generally less hazardous than stratovolcanoes, can still pose risks such as lava flows that can destroy infrastructure and vegetation, as well as the emission of volcanic gases that can affect air quality
Example: The 2018 eruption of Kilauea in Hawaii destroyed over 700 homes and covered large areas with lava flows
Both types of volcanoes can cause volcanic earthquakes and ground deformation, which can damage buildings and infrastructure in nearby areas
Volcanic earthquakes are caused by the movement of magma and volcanic gases within the volcano
The collapse of volcanic edifices, particularly in the case of stratovolcanoes with unstable slopes, can trigger massive landslides and debris avalanches
Example: The collapse of the northern flank of Mount St. Helens in 1980 triggered a massive debris avalanche that traveled up to 25 km from the volcano
Secondary hazards, such as the formation of acid rain from volcanic gases and the contamination of water sources by volcanic ash, can have long-term environmental and health impacts in the affected regions
Volcanic gases such as sulfur dioxide can react with water vapor in the atmosphere to form acid rain, which can harm vegetation and aquatic life
Notable Volcano Examples
Stratovolcanoes
Mount Fuji in Japan: An iconic stratovolcano known for its nearly perfect conical shape and cultural significance
Mount Vesuvius in Italy: Famous for its eruption in 79 AD that buried the cities of Pompeii and Herculaneum
Mount St. Helens in the United States: Experienced a catastrophic eruption in 1980 that removed the upper 400 m of the volcano and triggered a massive debris avalanche
in Mexico: An active stratovolcano located near Mexico City, with frequent small-scale eruptions and ash emissions
in Indonesia: Its 1883 eruption was one of the most violent in recorded history, generating massive tsunamis and affecting global climate
Shield Volcanoes
Mauna Loa and Kilauea in Hawaii, United States: Two of the world's most active volcanoes, known for their frequent lava flow eruptions and ongoing volcanic activity
on Mars: The largest known in the solar system, with a height of nearly 22 km and a diameter of over 600 km
in the Galapagos Islands, Ecuador: A young, active shield volcano that has experienced frequent eruptions since its discovery in the 16th century
in Iceland: A classic example of a shield volcano, with a broad, flat summit area and gently sloping flanks formed by numerous basaltic lava flows
Some volcanoes, such as Mount Etna in Italy, exhibit characteristics of both stratovolcanoes and shield volcanoes, showcasing the complexity and diversity of volcanic systems. Mount Etna has a complex morphology resulting from its long eruptive history and the interplay between explosive and effusive eruptions.
Key Terms to Review (27)
Basalt: Basalt is a dark, fine-grained volcanic rock that forms from the rapid cooling of low-viscosity lava. It is the most abundant volcanic rock on Earth and primarily constitutes the oceanic crust, playing a crucial role in the formation of various landforms and features associated with different tectonic settings.
Caldera: A caldera is a large, depression formed when a volcano erupts and collapses, typically resulting from the emptying of a magma chamber beneath the volcano. These features can vary in size and shape, often forming lakes or new volcanic landforms over time, and are key indicators of the volcanic processes that create explosive eruptions and diverse volcanic products.
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.
Fernandina: Fernandina is one of the youngest and most active volcanoes in the Galápagos Islands, characterized as a shield volcano. It showcases broad, gently sloping sides formed by low-viscosity basaltic lava flows, which allows it to cover a large area while maintaining a relatively low profile compared to stratovolcanoes.
Gentle slopes: Gentle slopes refer to the gradual incline of a volcano's surface, typically associated with certain types of volcanic structures. These slopes are often characteristic of shield volcanoes, which form from the accumulation of low-viscosity lava that flows over long distances. This feature allows for a broad, dome-like shape that distinguishes shield volcanoes from other types of volcanoes, such as stratovolcanoes, which have steeper profiles due to their composition and eruption styles.
Kilauea: Kilauea is one of the most active shield volcanoes in the world, located on the Big Island of Hawaii. Known for its frequent eruptions and low-viscosity lava flows, Kilauea exemplifies the characteristics of shield volcanoes, which typically have broad, gently sloping sides formed by the eruption of fluid basalt lava. Its activity not only shapes the Hawaiian landscape but also provides insight into volcanic processes and hazards.
Krakatoa: Krakatoa is a volcanic island located in the Sunda Strait between Java and Sumatra in Indonesia, known for its catastrophic eruption in 1883 that is considered one of the deadliest volcanic events in recorded history. This eruption had a significant impact on global climate, atmospheric conditions, and volcanic science, influencing our understanding of stratovolcanoes, pyroclastic deposits, and caldera formation.
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 dome: A lava dome is a steep-sided, mound-like volcanic structure formed by the slow extrusion of viscous lava, typically andesitic, dacitic, or rhyolitic in composition. These formations are created when the lava is too thick to flow far from the eruption site, leading to the accumulation of lava near the vent. Lava domes can be associated with explosive eruptions, and they often exhibit unique growth patterns and collapse features, making them significant in understanding volcanic processes.
Lava flow: A lava flow is the movement of molten rock (lava) that erupts from a volcano and flows down its slopes or spreads out across the ground. This geological phenomenon is crucial for understanding the various volcanic hazards, the formation of different landforms, and the impact on surrounding environments.
Magma composition: Magma composition refers to the chemical makeup of magma, which is a molten rock found beneath the Earth's surface. This composition plays a crucial role in determining the behavior of volcanic eruptions, including the type of volcano formed and the nature of volcanic activity. Various factors, such as temperature, pressure, and the presence of water and gases, influence magma composition, which in turn impacts eruption style, lava flow characteristics, and even the potential for explosive events.
Mauna Loa: Mauna Loa is one of the largest shield volcanoes on Earth, located on the Big Island of Hawaii. This volcano is characterized by its broad, gentle slopes formed by the eruption of low-viscosity basalt lava, which allows it to cover large areas with relatively few steep sections. As an active volcano, Mauna Loa plays a crucial role in understanding volcanic activity and magma dynamics.
Mount Fuji: Mount Fuji is an iconic stratovolcano located on Honshu Island in Japan, standing at 3,776 meters (12,389 feet), making it the tallest mountain in the country. Known for its symmetrical cone shape and cultural significance, Mount Fuji is a prime example of a stratovolcano formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate, which connects it to various geological processes and volcanic activity in Japan.
Mount St. Helens: Mount St. Helens is an active stratovolcano located in the state of Washington, known for its catastrophic eruption on May 18, 1980, which significantly altered the surrounding landscape. This volcano is a classic example of stratovolcanic activity and provides insights into volcanic behavior, pyroclastic flows, and tephra dispersal patterns associated with eruptions.
Mount Vesuvius: Mount Vesuvius is an active stratovolcano located on the west coast of Italy, best known for its catastrophic eruption in 79 AD that buried the cities of Pompeii and Herculaneum. This volcano is part of the Campanian volcanic arc and is characterized by its steep profile and explosive eruptions, distinguishing it from shield volcanoes that typically have more fluid lava flows.
Olympus Mons: Olympus Mons is the tallest volcano and the largest shield volcano in the solar system, located on the planet Mars. It stands approximately 22 kilometers (13.6 miles) high, which is nearly three times taller than Mount Everest, and features a diameter of about 600 kilometers (373 miles). This massive structure provides critical insights into volcanic activity and geological processes on Mars compared to terrestrial volcanoes.
Popocatépetl: Popocatépetl is an active stratovolcano located in central Mexico, known for being the second-highest peak in the country. Its name means 'Smoking Mountain' in the Nahuatl language, which reflects its frequent eruptions and the plume of smoke and ash that it emits. As a stratovolcano, Popocatépetl is characterized by its steep, conical shape and is primarily composed of layers of hardened lava, volcanic ash, and tephra.
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.
Quiet eruption: A quiet eruption is a type of volcanic activity characterized by the relatively gentle release of lava, typically low in viscosity, allowing it to flow easily from the volcano. This type of eruption is often associated with shield volcanoes and results in broad, gentle slopes rather than explosive formations. Quiet eruptions can produce extensive lava flows and create large lava plateaus, contributing to the landscape in significant ways.
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.
Skjaldbreiður: Skjaldbreiður is a type of shield volcano characterized by its broad, dome-like shape and gentle slopes formed by the eruption of low-viscosity basaltic lava. This volcanic structure is notable for its extensive lava flows that spread out over large areas, making it distinct from other volcanic forms. The term translates to 'broad shield' in Icelandic, reflecting its physical appearance and the way it builds up over time through repeated eruptions.
Steep slopes: Steep slopes refer to the sharply inclined surfaces of volcanic landforms, which are characterized by their angle of inclination being significantly greater than that of gentler slopes. These slopes play a crucial role in determining the overall structure and eruption style of different types of volcanoes, as they influence the flow dynamics of lava and the potential for volcanic hazards such as landslides and pyroclastic flows.
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.
Subduction: Subduction is the geological process in which one tectonic plate moves under another and sinks into the mantle, typically occurring at convergent plate boundaries. This process is crucial for understanding the recycling of Earth's materials, driving volcanic activity, and forming mountain ranges. It leads to various geological phenomena, including earthquakes and the creation of deep ocean trenches, making it a key element in the study of Earth's internal processes and plate tectonics.
Tefra: Tefra refers to the solid volcanic materials that are ejected into the atmosphere during a volcanic eruption. This term encompasses a range of materials, including ash, pumice, and volcanic rock fragments, which can be dispersed over large areas depending on the eruption's intensity and wind conditions. Tefra plays a significant role in shaping the landscape around stratovolcanoes and shield volcanoes, influencing both geological processes and ecological dynamics in affected regions.
Volcanic ash fallout: Volcanic ash fallout refers to the accumulation of fine volcanic ash particles that are ejected during explosive volcanic eruptions and settle back to the ground as a result of gravity. This phenomenon is significant as it can have widespread impacts on the environment, air quality, and human health, while also playing a role in shaping various volcanic landforms and influencing geological processes.