4.2 Volcanic processes and types of eruptions
3 min read•august 7, 2024
Volcanoes are Earth's fiery architects, shaping landscapes through explosive and effusive eruptions. They spew magma, gases, and pyroclastic material, creating diverse landforms like towering stratovolcanoes and sprawling shield volcanoes.
Volcanic hazards pose significant risks to human life and infrastructure. From fast-moving lahars and pyroclastic flows to toxic gases and destructive flows, these phenomena demand our respect and careful monitoring.
Volcanic Materials
Magma and Lava
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- Magma molten rock beneath Earth's surface contains dissolved gases and sometimes crystals
- Composition of magma influences its viscosity and behavior
- Felsic magma high silica content, more viscous, often associated with explosive eruptions
- Mafic magma low silica content, less viscous, often associated with effusive eruptions
- Lava magma that has been erupted onto Earth's surface
- As lava cools, it solidifies into various igneous rocks (basalt, obsidian)
Pyroclastic Material and Volcanic Gases
- Pyroclastic material fragments of rock ejected during an explosive volcanic eruption
- Includes ash (particles < 2mm), lapilli (2-64mm), and bombs/blocks (> 64mm)
- Pyroclastic density currents (pyroclastic flows) fast-moving, ground-hugging flows of hot ash, pumice, and gas
- Volcanic gases released during eruptions, primarily water vapor, carbon dioxide, and sulfur dioxide
- Can contribute to air pollution and affect climate (sulfur dioxide can lead to global cooling)
- Acid rain can result from volcanic gases mixing with atmospheric moisture
Volcanic Landforms
Stratovolcanoes and Shield Volcanoes
- (composite volcano) steep-sided, conical volcano built by layers of lava, ash, and pyroclastic material
- Typically associated with subduction zones and explosive eruptions (Mount St. Helens, Mount Fuji)
- Can reach heights of several thousand meters
- broad, gently sloping volcano built primarily from fluid lava flows
- Associated with hotspots and effusive eruptions (Mauna Loa, Olympus Mons on Mars)
- Can cover large areas and reach significant heights (Mauna Loa is over 9 km tall from base to summit)
Calderas
- Caldera large, circular depression formed by the collapse of a volcano's summit or the emptying of its magma chamber
- Can occur during or after large-scale explosive eruptions (Yellowstone, Crater Lake)
- Some calderas can be several kilometers in diameter and hundreds of meters deep
- Over time, calderas may fill with water to form lakes or with new volcanic material during subsequent eruptions
Eruption Types
Effusive and Explosive Eruptions
- characterized by the outpouring of fluid lava with little to no explosive activity
- Often associated with mafic magmas and shield volcanoes (Kilauea, Iceland)
- Lava flows can travel long distances and cover large areas
- characterized by the violent fragmentation and ejection of magma and rock
- Often associated with felsic magmas and stratovolcanoes (Mount Pinatubo, Krakatoa)
- Driven by the rapid expansion of dissolved gases in the magma
- Can produce tall eruption columns, pyroclastic density currents, and extensive ash fall
Volcanic Hazards
Lahars and Pyroclastic Material
- Lahars volcanic mudflows or debris flows, often triggered by the rapid melting of snow and ice during an eruption
- Can travel long distances at high speeds, causing significant damage and loss of life (Nevado del Ruiz, 1985)
- Can also be triggered by heavy rainfall on loose volcanic debris
- Pyroclastic material ejected during explosive eruptions poses a significant hazard
- Pyroclastic density currents can travel at speeds over 100 km/hr, destroying everything in their path (Pompeii, 79 CE)
- Ash fall can cause respiratory issues, damage infrastructure, and disrupt transportation (Eyjafjallajökull, 2010)
Volcanic Gases and Lava Flows
- Volcanic gases can pose health risks and contribute to air pollution
- High concentrations of sulfur dioxide and other gases can cause respiratory issues and acid rain (Kilauea, 2018)
- Carbon dioxide emissions from Lake Nyos (Cameroon) in 1986 led to the asphyxiation of over 1,700 people
- Lava flows can destroy property and infrastructure in their path
- Speed and extent of damage depend on the lava's composition and volume (Eldfell, Iceland, 1973)
- In some cases, lava flows can be diverted or slowed using barriers and water cooling (Etna, Sicily, 1992)
Key Terms to Review (18)
David Pyle: David Pyle is a prominent volcanologist known for his extensive research on volcanic processes and eruption dynamics. His work has significantly contributed to the understanding of how volcanoes behave, including the factors that influence their eruptions and the types of volcanic activity that can occur. Through his studies, Pyle has helped to develop models that predict volcanic behavior, enhancing both scientific knowledge and public safety related to volcanic hazards.
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 lava flows and basaltic landforms. Unlike explosive eruptions, which eject ash and gas violently into the atmosphere, effusive eruptions allow lava to escape steadily from the vent, creating broad, shield-like volcanoes. This type of eruption typically occurs at hotspots or along divergent tectonic plate boundaries where magma is less viscous and can flow more easily.
Explosive eruption: An explosive eruption is a volcanic event characterized by the violent expulsion of gas, ash, and molten rock from a volcano. This type of eruption occurs when magma rises to the surface and encounters high pressure, leading to rapid decompression and the forceful release of volcanic materials. Explosive eruptions are often associated with stratovolcanoes and can have devastating impacts on the surrounding environment and human populations.
GPS Monitoring: GPS monitoring refers to the use of Global Positioning System technology to track the movement and location of geological features, including volcanic activity. This technology allows scientists to gather precise data on ground deformation, which is crucial for understanding volcanic processes and predicting types of eruptions. By providing real-time information about the positioning of the Earth’s surface, GPS monitoring plays a key role in assessing volcanic hazards and implementing safety measures for nearby populations.
John C. H. Wang: John C. H. Wang is a prominent volcanologist known for his extensive research in volcanic processes and the dynamics of eruptions. His work has contributed to a better understanding of magma behavior, eruption prediction, and the environmental impacts of volcanic activity, linking his studies directly to various volcanic processes and types of eruptions.
Lahar: A lahar is a volcanic mudflow or debris flow that occurs when volcanic material mixes with water, often from melted snow, ice, or heavy rainfall. Lahars can be extremely destructive, flowing down the slopes of a volcano and into river valleys, carrying with them a mix of ash, rock, and debris. This process highlights the hazards associated with volcanic activity and the significant impact it can have on surrounding landscapes and communities.
Lava: Lava is molten rock that erupts onto the Earth's surface during a volcanic eruption. Once it flows out of a volcano, lava can vary in composition, temperature, and viscosity, influencing the type of eruption and the landscape it creates. The properties of lava directly affect volcanic processes, such as whether an eruption is explosive or effusive, and how lava solidifies into different landforms like lava tubes or basalt plateaus.
Magma formation: Magma formation is the process by which molten rock material, or magma, is generated beneath the Earth's surface due to the melting of rocks in the mantle and crust. This formation occurs primarily due to factors such as temperature, pressure, and the presence of volatiles, which influence the melting point of rocks. Understanding magma formation is crucial for comprehending volcanic processes and the types of eruptions that can occur when magma rises to the surface.
Monitoring techniques: Monitoring techniques are systematic methods used to observe, measure, and analyze volcanic activity and related phenomena to understand eruptions and their potential impacts. These techniques include a range of tools and approaches, such as remote sensing, seismic monitoring, gas emissions analysis, and ground deformation measurements, which help predict volcanic eruptions and assess risks to surrounding areas.
Pyroclastic flow: A pyroclastic flow is a fast-moving current of hot gas and volcanic matter that flows down the slopes of a volcano during an explosive eruption. These flows can reach speeds of up to 700 km/h (about 435 mph) and are extremely dangerous due to their high temperatures, which can exceed 1,000 °C (1,832 °F). Pyroclastic flows are a critical aspect of volcanic processes, as they are one of the primary hazards associated with certain types of eruptions.
Risk Assessment: Risk assessment is the systematic process of evaluating potential risks that may be involved in a projected activity or undertaking. In the context of volcanic processes and types of eruptions, it involves analyzing the likelihood and consequences of volcanic hazards, such as lava flows, ashfall, and pyroclastic flows, to inform preparedness and response strategies for affected communities. This assessment helps to prioritize resources and develop mitigation plans to minimize the impact of volcanic events on human life and infrastructure.
Seismology: Seismology is the scientific study of earthquakes and the propagation of seismic waves through the Earth. It involves understanding the mechanisms that cause earthquakes, how seismic waves travel, and what these waves reveal about the Earth's internal structure and composition. This field also plays a crucial role in assessing volcanic activity and potential eruptions, as seismic data can indicate movement beneath the surface.
Shield volcano: A shield volcano is a broad, domed volcano characterized by gentle slopes and primarily constructed by the eruption of low-viscosity basalt lava that can flow over great distances. This type of volcano is formed from repeated, non-explosive eruptions that build up layers of lava, leading to its unique shield-like shape. Shield volcanoes are significant because they offer insights into volcanic processes and can produce large amounts of lava with relatively low levels of explosiveness.
Stratovolcano: A stratovolcano, also known as a composite volcano, is a conical volcano characterized by its steep profile and periodic explosive eruptions. These volcanoes are formed from alternating layers of solidified lava flows, volcanic ash, and other volcanic debris, which creates a stratified structure. The composition of the erupted materials is typically more viscous, leading to more explosive eruptions compared to other types of volcanoes.
Tectonic plate boundaries: Tectonic plate boundaries are the edges where two tectonic plates meet, and they are crucial in shaping the Earth's surface. These boundaries can lead to various geological activities, including earthquakes, volcanic eruptions, and the formation of mountain ranges. Understanding these boundaries helps explain the processes behind volcanic activity and the different types of eruptions that can occur depending on the nature of the boundary interaction.
Tephra: Tephra refers to the solid volcanic material that is ejected during an explosive volcanic eruption, which can include ash, pumice, and volcanic rock fragments. This material can vary greatly in size, from fine ash particles that can be carried by the wind over long distances to larger volcanic bombs that fall close to the volcano. Understanding tephra is crucial for recognizing the processes involved in different types of eruptions and their potential impacts on the surrounding environment and human activities.
Volcanic ash fallout: Volcanic ash fallout refers to the fine particles of volcanic rock, minerals, and glass that are ejected into the atmosphere during a volcanic eruption and eventually settle back to the ground. This ash can travel vast distances depending on wind patterns and eruption intensity, impacting air quality, agriculture, and human health in areas far from the volcano itself. Understanding volcanic ash fallout is essential for assessing the risks associated with different types of eruptions and their potential effects on the environment and communities.
Volcanic gas emissions: Volcanic gas emissions refer to the release of gases from a volcano during its eruptive activity or through passive venting. These emissions can include water vapor, carbon dioxide, sulfur dioxide, and other gases, playing a significant role in both volcanic processes and types of eruptions. The composition and volume of these gases can influence the behavior of eruptions, affect climate, and impact air quality in surrounding areas.