Igneous Rocks: Melting and Magma Formation

• Melting points of rocks are affected by temperature and pressure
• Chemical composition also affects melting points of rocks
• Geothermal gradient is the rate at which temperature increases with depth

Melting Processes

• Fractional melt is when a rock is partly melted, creating a mix of molten and solid material
• Fractionation separates the melt from the remaining solid material during melting
• Magma chambers are reservoirs of magma where melting occurs under temperatures of 800–1000°C

Magma vs. Lava

• Magma is molten rock below the Earth’s surface
• Lava is magma that reaches the surface during an eruption

Magma Types & Their Properties

• Basaltic magma has a low silica content
• Andesitic magma has a medium silica content
• Rhyolitic magma has a high silica content
• Rhyolitic magma has a high viscosity and is very resistant to flow
• Basaltic magma eruptions are typically Hawaiian/Icelandic (Fissure) Eruptions, low-viscosity basaltic lava that flows easily
• Rhyolitic magma eruptions are highly explosive and produces large amounts of ash

Eruption Styles:

• Plinian eruptions are explosive with high ash columns
• Strombolian eruptions are mildly explosive with gas-rich magma
• Vulcanian eruptions are more explosive and can produce pyroclastic flows
• Hawaiian/Icelandic (Fissure) Eruptions feature low-viscosity basaltic lava that flows easily

Volcanic Materials:

• Pyroclasts/Tephra includes bombs, lapilli, and ash
• Agglomerates and tuff differ by ash content in the solidified volcanic rock

Key Concepts

• Viscosity is primarily controlled by silica content and temperature
• Viscosity affects eruption style
• Hazards: Pyroclastic flows, volcanic gases, and secondary effects like mudslides or fires
• Benefits: Soil fertility improvement, geothermal energy, and mineral deposits

Plate Tectonic Model

• Earth’s lithosphere is made of rigid plates that move over the weaker asthenosphere
• Lithosphere is the rigid outer layer of the Earth
• Asthenosphere is the weaker, more ductile layer beneath the lithosphere
• Isostasy is the balance between Earth’s crust and mantle

Continental Drift

• Alfred Wegener's hypothesis posits that continents slowly drift across the Earth’s surface
• Evidence includes matching rock formations, fossil distributions like Glossopteris and Mesosaurus, and glacial deposits
• Pangaea was the supercontinent that later split into today’s continents

Seafloor Spreading

• New oceanic crust is formed at mid-ocean ridges
• Rock ages increase with distance from the spreading center

Types of Plate Boundaries:

• Divergent boundaries occur where plates move apart
• Transform boundaries occur where plates slide past each other
• Convergent boundaries occur where plates collide
• Subduction zones: One plate sinks beneath another
• Continental collision zones: Two continental plates converge, creating high mountain ranges
• Mantle Convection drives plate motion through heat transfer via conduction and convection currents

Earthquake Mechanics

• Elastic Rebound Theory: Stress builds along faults until rocks suddenly snap back, releasing energy as an earthquake
• Focus (Hypocenter) is the point beneath the surface where the earthquake begins
• Epicenter is the point directly above the focus on Earth’s surface

Seismic Waves

• P waves are the fastest and can travel through solids, liquids, and gases
• S waves are slower than P waves and do not travel through liquids
• Surface waves travel along Earth’s surface and are often responsible for most of the damage

Seismology Tools and Measurements

• Seismograph is an instrument that records ground movement
• Seismogram is the output recording of the seismic activity
• Richter Scale is a logarithmic measure of wave amplitude
• Moment Magnitude Scale considers rupture size, rock properties, and fault displacement
• Modified Mercalli Intensity Scale is based on observed effects and damage

Additional Key Concepts

• Isotherms are lines connecting points of equal temperature
• Tectonic Cycle (Wilson Cycle) describes the cyclical opening and closing of ocean basins and the formation/breakup of supercontinents over roughly 200 million years