7.2 Types of Calderas and Their Evolution

Calderas come in three main flavors: collapse, explosion, and erosion. Each type forms differently and has unique features. Understanding these differences is key to grasping how supervolcanoes shape our planet's surface.

Calderas evolve through stages, from pre-caldera buildup to post-caldera quiet periods and potential reawakening. This lifecycle helps us predict future volcanic activity and assess risks to nearby communities. It's a crucial part of studying supervolcanoes.

Caldera Types and Formation

Collapse Calderas

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• Form when a magma chamber is partially emptied, leading to the unsupported roof collapsing into the void
• Examples include Crater Lake (USA) and Aso (Japan)
• Typically larger than explosion calderas, as they are related to the size of the underlying magma chamber
• Often associated with silicic magmas (rhyolitic to dacitic)

Explosion Calderas (Krakatoa-type)

• Form during explosive volcanic eruptions when the magma chamber is completely emptied, and the overlying rock is blasted away
• Examples include Krakatoa (Indonesia) and Santorini (Greece)
• Usually smaller than collapse calderas and may have a more irregular shape due to the explosive nature of their formation
• Can be associated with a wider range of magma compositions (basaltic to rhyolitic)

Erosion Calderas (Glencoe-type)

• Form when a volcanic edifice is heavily eroded, exposing the underlying magma chamber
• An example is Glencoe Caldera (Scotland)
• Have a more irregular or dissected morphology compared to the more circular or elliptical shape of collapse and explosion calderas
• Formation process differs from collapse and explosion calderas, as they form through erosion rather than a singular eruptive event

Caldera Morphology

• Varies depending on the formation process and can be characterized by size, shape, and the presence of resurgent domes or post-caldera volcanism
• Collapse calderas are typically larger and more circular or elliptical in shape
• Explosion calderas are usually smaller and may have a more irregular shape
• Erosion calderas have a more irregular or dissected morphology due to the erosional processes involved in their formation

Caldera Development Stages

Pre-caldera Volcanism

• Involves the buildup of a volcanic edifice through repeated eruptions from a central vent or multiple vents
• Characterized by the accumulation of lava flows, pyroclastic deposits, and the growth of a magma chamber
• Sets the stage for the caldera-forming eruption by creating an unstable magmatic system

Caldera-forming Eruptions

• Occur when the magma chamber becomes unstable, leading to large-scale evacuation of magma and the collapse of the overlying rock
• Can be highly explosive and produce extensive pyroclastic deposits
• Result in the formation of the caldera structure, which may be a collapse caldera, explosion caldera, or erosion caldera

Post-caldera Quiescence

• Immediately following the caldera-forming eruption, the caldera may experience a period of reduced activity
• The caldera floor may be filled with volcanic deposits, water (forming a caldera lake), or sediments
• This stage represents a period of relative stability in the caldera system

Post-caldera Volcanism

• Can occur within the caldera or along its margins
• May include the formation of resurgent domes, lava domes, or cinder cones, as well as the eruption of lava flows and pyroclastic materials
• Indicates that the magmatic system is still active and evolving
• The presence and nature of post-caldera volcanism can vary between caldera types

Long-term Evolution

• The caldera may undergo further collapse or erosion over time, modifying its original morphology
• Hydrothermal activity and mineralization may also occur during the post-caldera stage
• The caldera system continues to evolve over time, influenced by factors such as magma recharge, regional stress fields, and erosional processes

Caldera Types: Comparison and Contrast

Formation Mechanisms

• Collapse calderas form due to the emptying and collapse of a magma chamber
• Explosion calderas form during explosive eruptions that completely evacuate the magma chamber
• Erosion calderas form through the erosion of a volcanic edifice rather than a singular eruptive event

Size and Shape

• Collapse calderas are typically larger than explosion calderas, related to the size of the underlying magma chamber
• Explosion calderas are usually smaller and may have a more irregular shape due to the explosive nature of their formation
• Erosion calderas have a more irregular or dissected morphology compared to the more circular or elliptical shape of collapse and explosion calderas

Post-caldera Volcanism

• Collapse calderas often experience resurgent doming and the formation of lava domes
• Explosion calderas may have more dispersed post-caldera volcanism along the caldera margins
• The presence and nature of post-caldera volcanism can vary between caldera types

Magma Composition

• Collapse calderas are often related to silicic magmas (rhyolitic to dacitic)
• Explosion calderas can be associated with a wider range of magma compositions (basaltic to rhyolitic)
• The composition of the magma can influence the style and intensity of eruptions, as well as the morphology of the resulting caldera

Caldera Activity: Future Potential

Factors Influencing Future Activity

• The presence of an active magma chamber, the rate of magma recharge, and the state of stress in the overlying rock
• Increased seismicity, ground deformation, and changes in gas emissions may indicate magma movement or pressurization of the system
• The recurrence interval of caldera-forming eruptions and the time elapsed since the last major eruption can provide a general guide to the potential for future activity

Monitoring Techniques

• Seismicity monitoring, particularly earthquake swarms or tremor, may indicate magma movement or pressurization
• Ground deformation, detected through GPS, InSAR, or tiltmeters, can reveal inflation or deflation of the caldera floor related to magma intrusion or withdrawal
• Gas emission monitoring, such as SO2 or CO2 flux, can suggest magma degassing and potential unrest
• These techniques provide insights into the current state of a caldera system and help assess the likelihood of future eruptions

Indicators of Potential Future Activity

• The presence of active hydrothermal systems, resurgent doming, or recent post-caldera volcanism may indicate a higher likelihood of future activity
• Calderas that have been dormant for long periods may have a lower potential for future activity compared to those with recent unrest
• However, each caldera system is unique, and the timing of eruptions can be highly variable

Multidisciplinary Approach

• Evaluating the potential for future activity in caldera systems requires integrating geological, geophysical, and geochemical data
• Developing a comprehensive understanding of the system's behavior and evolution over time is crucial for assessing future eruption potential
• Collaborations between volcanologists, geophysicists, geochemists, and other experts are essential for effective caldera monitoring and hazard assessment