Magma and Volcanism Overview

Magma and Volcanism

• Earth's internal heat drives geological processes, including volcanism and plate tectonics
• Rocks on Earth's surface are typically solid, but rocks exist in a liquid state deep within the Earth
• Molten rocks beneath the Earth's surface are called magma
• Magma is less dense than surrounding solid rock, enabling it to rise towards the surface
• When magma reaches the surface, it is called lava
• Magma's ability to flow is called viscosity
• Viscosity is impacted by silica content; higher silica equals higher viscosity
• Higher temperature magma has lower viscosity, flowing more readily
• Magmas form deep inside the crust and upper mantle when conditions are right for pre-existing solid rock to melt
• Three ways magma is generated:
  • Decompression melting: Temperature stays the same, but pressure decreases
  • Flux melting: Addition of volatile (gaseous) substances to hot solid rock
  • Heat transfer melting: Very hot magma brings additional heat to surrounding rock, causing it to melt

Formation of Magma

• Rocks melt over a range of temperatures
• The melting temperature of rock (eutectic temperature) is lower than its constituent minerals
• Partial melting occurs when only certain minerals in a rock melt
• The rock completely melts when temperature reaches a sufficient level

Fractionation

• If magma separates from rock that hasn't fully melted, the magma will contain components that melted at lower temperatures, while the remaining rock will contain components with higher melting temperatures

Volcano

• Volcanoes are visible manifestations of rock formation
• A volcano's vent acts as a conduit for lava/molten rock to reach the surface
• The funnel-shaped depression where materials are ejected is called a crater
• Eruptions are events when lava spews out of a volcano
• Two types of eruptions:
  • Effusive: Dominated by lava flow and lava fountains
  • Explosive: Ejects ash and pyroclastic fragments, forming ash clouds
• Lava composition impacts eruption type
  • Low silica = less viscous, effusive eruptions
  • High silica = more viscous, explosive eruptions

Three Types of Volcanoes

• Shield volcanoes: Broad, dome-shaped with gentle slopes, covering wide areas
• Cinder cone volcanoes: Conical hills composed of granular materials formed by lava fountains erupted from a single vent
• Stratovolcanoes (composite volcanoes): Steep-sided, cone-shaped; formed by viscous, sticky lava

Metamorphism

• Metamorphism: The process where a rock's form changes into a new one without melting
• Metamorphism implies change occurs in a solid state. 
• Metamorphism involves processes over thousands to millions of years
• Three main processes:
  • Recrystallization: Changes in shape and size of minerals without changing the mineral's identity
  • Phase change: Transformation of one mineral grain into another with the same composition but different crystal structure (e.g., coesite from quartz)
  • Neocrystallization: Growth of new minerals differing from those in the protolith (original rock)
  • Pressure solution: Mineral grains dissolve under pressure in the presence of water
  • Plastic deformation: Mineral grains become flattened or elongated without altering composition or structure due to high temperature and pressure

Causes of Metamorphism

• High temperatures cause atoms to vibrate rapidly, stretching and bending chemical bonds
• Bonds breaking allows atoms to detach and form new bonds with other atoms, leading to rearrangement within the mineral or migration into other minerals
• Recrystallization and neocrystallization are consequences of atomic rearrangement

Types of Metamorphism

• Contact metamorphism: Rock minerals and textures changed by heat due to contact with magma
• Regional metamorphism: Rock minerals and textures changed by pressure over a wide area or region (e.g., from converging tectonic plates)

Explore the fascinating world of magma and volcanism in this quiz. Learn about the formation of magma, its properties like viscosity, and how it influences volcanic activity. Test your knowledge on geological processes driven by Earth's internal heat.