🌋Volcanology Unit 7 – Calderas and Supervolcanoes

What Are Calderas and Supervolcanoes?

• Calderas are large volcanic depressions formed by the collapse of a volcano's summit or the emptying of its magma chamber
• Typically circular or oval-shaped, with diameters ranging from a few kilometers to over 100 km (Yellowstone Caldera)
• Supervolcanoes are volcanoes capable of producing exceptionally large volcanic eruptions, often associated with the formation of calderas
• Eject more than 1,000 cubic kilometers (240 cubic miles) of material in a single eruption (Toba eruption ~74,000 years ago)
• Volcanic Explosivity Index (VEI) of 8, the highest level on the scale
• Can have global impacts on climate, ecosystems, and human societies
• Characterized by their ability to generate massive amounts of volcanic ash, pumice, and volcanic gases

Formation and Structure

• Calderas form when a volcano's magma chamber is partially or completely emptied during an eruption
• As magma is evacuated, the overlying rock and soil collapse into the empty space, creating a large depression
• Magma chamber roof becomes unsupported and collapses under its own weight
• Ring fractures develop around the collapsing area, allowing for further subsidence
• Resurgent doming may occur post-collapse, as magma intrudes and uplifts the caldera floor (Valles Caldera, New Mexico)
• Caldera size depends on the volume of magma evacuated and the depth of the magma chamber
• Larger magma chambers generally result in larger calderas
• Calderas can be filled with volcanic ash, pumice, and ignimbrite deposits from the eruption that formed them

Types of Calderas

• Crater Lake type (Crater Lake, Oregon)
  • Formed by the collapse of a stratovolcano's summit after a large eruption
  • Often characterized by steep walls and a deep, circular lake
• Valles type (Valles Caldera, New Mexico)
  • Formed by the eruption of large volumes of silicic magma, leading to the collapse of the magma chamber roof
  • Resurgent doming may occur post-collapse
• Galapagos type (Fernandina Caldera, Galapagos Islands)
  • Formed by the gradual subsidence of a volcano's summit due to magma withdrawal
  • Characterized by a shallow, saucer-shaped depression
• Basaltic shield calderas (Kilauea Caldera, Hawaii)
  • Formed by the collapse of the summit of a basaltic shield volcano
  • Often smaller in size compared to other caldera types
• Ash-flow calderas (La Garita Caldera, Colorado)
  • Formed by the eruption of large volumes of ash and pumice, leading to the collapse of the magma chamber roof
  • Associated with extensive ignimbrite deposits

Famous Calderas and Supervolcanoes

• Yellowstone Caldera (Wyoming, USA)
  • Formed by three major eruptions 2.1 million, 1.3 million, and 640,000 years ago
  • Measures 55 km by 72 km (34 mi by 45 mi)
• Toba Caldera (Sumatra, Indonesia)
  • Formed by a massive eruption ~74,000 years ago, possibly causing a global volcanic winter
  • Measures 100 km by 30 km (62 mi by 19 mi)
• Taupo Caldera (North Island, New Zealand)
  • Formed by the Oruanui eruption ~26,500 years ago, one of the world's largest known eruptions
  • Measures 35 km by 50 km (22 mi by 31 mi)
• Aira Caldera (Kyushu, Japan)
  • Formed by a massive eruption ~22,000 years ago
  • Measures 20 km by 25 km (12 mi by 16 mi)
• Long Valley Caldera (California, USA)
  • Formed by the Bishop Tuff eruption ~760,000 years ago
  • Measures 32 km by 17 km (20 mi by 11 mi)

Eruption Mechanisms and Processes

• Magma composition plays a crucial role in caldera-forming eruptions
• Silicic magmas (high in silica content) are more viscous and can trap gases, leading to explosive eruptions
• Mafic magmas (low in silica content) are less viscous and allow gases to escape more easily, resulting in less explosive eruptions
• Magma chamber overpressure can trigger caldera-forming eruptions
• As magma rises and accumulates in the chamber, pressure builds up
• When the pressure exceeds the strength of the overlying rock, an eruption occurs
• Magma withdrawal during an eruption leads to the collapse of the magma chamber roof
• As magma is evacuated, the overlying rock loses support and collapses into the empty space
• Pyroclastic flows are common during caldera-forming eruptions
• These are fast-moving, ground-hugging flows of hot ash, pumice, and volcanic gases
• Can travel at speeds up to 700 km/h (450 mph) and reach temperatures of 1,000°C (1,830°F)
• Ignimbrite deposits are formed by the deposition and welding of pyroclastic flow material
• These deposits can cover vast areas and reach thicknesses of hundreds of meters

Hazards and Environmental Impacts

• Caldera-forming eruptions can have devastating local and global impacts
• Pyroclastic flows can bury and destroy everything in their path, causing significant loss of life and property damage
• Volcanic ash can cause respiratory issues, damage infrastructure, and disrupt air travel
• Ash fallout can cover vast areas, smothering vegetation and impacting agriculture
• Volcanic gases (sulfur dioxide, carbon dioxide) can contribute to air pollution and acid rain
• Large-scale eruptions can inject ash and sulfur dioxide into the stratosphere
• Sulfur dioxide can react with water vapor to form sulfuric acid aerosols
• These aerosols can reflect sunlight, leading to global cooling and potential climate disruptions (volcanic winter)
• Caldera formation can also trigger earthquakes and landslides, further compounding the hazards

Monitoring and Prediction

• Monitoring calderas and supervolcanoes is crucial for hazard assessment and risk mitigation
• Seismic monitoring detects earthquakes and ground deformation related to magma movement
• GPS and InSAR measure ground deformation caused by magma intrusion or withdrawal
• Gas monitoring assesses changes in the composition and emission rates of volcanic gases
• These changes can indicate magma ascent or increased volcanic activity
• Hydrothermal monitoring tracks changes in the temperature, chemistry, and behavior of hot springs and geysers
• Geologic mapping and stratigraphic analysis help understand a caldera's eruptive history and potential future behavior
• Numerical modeling and simulations can aid in understanding the processes driving caldera formation and eruptions
• Despite advances in monitoring techniques, predicting the timing and magnitude of caldera-forming eruptions remains challenging

Cool Facts and Future Research

• The Yellowstone Caldera is home to over 10,000 hydrothermal features, including the iconic Old Faithful geyser
• The Toba eruption ~74,000 years ago may have caused a genetic bottleneck in human evolution
• Some scientists suggest that the global population was reduced to 3,000-10,000 individuals
• Crater Lake, formed by the collapse of Mount Mazama, is the deepest lake in the United States (594 m / 1,949 ft)
• The Long Valley Caldera is part of the Mono-Inyo Craters volcanic chain, which includes the youngest mountain range in North America (Mono Craters)
• Future research focuses on improving our understanding of the magmatic processes that lead to caldera-forming eruptions
• Developing better models for magma chamber dynamics, magma ascent, and eruption triggering mechanisms
• Enhancing monitoring techniques and early warning systems for caldera unrest and potential eruptions
• Assessing the potential impacts of future caldera-forming eruptions on climate, ecosystems, and human societies
• Exploring the geothermal energy potential of calderas and their associated hydrothermal systems