Plate Tectonics
What are tectonic plates and what layer do they float on?
Tectonic plates are large pieces of Earth's lithosphere that move on the mantle; they float on the mantle.
Define a mountain in geological terms
Large landforms that rise significantly above surrounding landscape.
Where do most volcanoes form on Earth?
Along divergent and convergent plate boundaries (and hotspots).
What causes an earthquake? Define both focus and epicenter.
Sudden release of energy when plates or faults slip; focus is the subsurface origin, epicenter is the surface point above it.
Who proposed continental drift and in what year? What was the name of the supercontinent he suggested?
Alfred Wegener, 1912; Pangaea.
Name and briefly describe the three main types of plate boundaries.
Divergent: plates move apart (mid-ocean ridges); Convergent: plates move together (subduction zones, mountains); Transform: plates slide past each other (strike-slip faults).
What is orogeny?
Orogeny is mountain-building, especially from continental collisions.
What is subduction and how does it lead to volcanic activity along continental margins?
Subduction is when one plate sinks beneath another; sinking oceanic lithosphere melts, generating magma that rises to form volcanic arcs on continents.
Describe the three main types of seismic waves (P, S, and surface) and mention which is typically most destructive.
P-waves: compressional, fastest, travel through solids/liquids; S-waves: shear, slower, only through solids; Surface waves: travel along surface, usually most destructive.
Give two lines of evidence Wegener used to support continental drift (one fossil and one geologic).
Fossil: Mesosaurus (found in South America and Africa); Geologic: matching rock formations/mountain chains (e.g., Appalachians and Caledonides).
Explain how mantle convection drives plate movement.
300 — Heat from Earth's interior causes convection currents in the mantle; hot material rises and cooler material sinks, creating forces that move plates.
Describe how folded mountains form and give a real-world example.
Folded mountains form under compressional stress at convergent boundaries; example: Himalayas or Appalachians
Name and contrast the three main types of volcanoes (shield, cinder cone, composite/stratovolcano).
Shield: broad, gentle slopes from low-viscosity lava; Cinder cone: small, steep cones from ejected pyroclasts; Composite/stratovolcano: tall, steep, alternating lava and ash layers, explosive eruptions.
Explain how seismographs are used to measure earthquakes.
Seismographs record seismic signals
Describe the concept of sea-floor spreading and name the scientist who proposed its modern hypothesis.
Sea-floor spreading: new crust forms at mid-ocean ridges and moves outward; Harry Hess proposed the hypothesis.
Describe what happens at a divergent plate boundary and name a feature that forms there.
At divergent boundaries, upwelling mantle creates new crust and mid-ocean ridges form (also rift valleys on continents).
Explain how fault-block mountains form and what type of stress creates them.
Fault-block mountains form when tensional stress pulls crust apart, large blocks drop and adjacent blocks tilt and uplift along normal faults.
Define a pluton and name four types of intrusive igneous bodies (brief descriptions).
Pluton: cooled magma body below surface. Types: dike (cuts across layers), sill (parallel between layers), batholith (very large intrusive body >40 mi²), laccolith (mushroom/dome-shaped intrusion), stock (smaller batholith).
What types of faults are associated with tensional, compressional, and shear stresses? Give one plate-boundary setting where each occurs.
Normal faults: tensional stress (divergent settings); Reverse/thrust faults: compressional stress (convergent settings); Strike-slip faults: shear stress (transform boundaries).
What is subduction and what three major geological phenomena are associated with plate boundaries as a result?
Subduction is the return of ocean floor to the mantle; associated phenomena: earthquakes, volcanism, mountain building.
Explain why ocean-floor rocks are youngest at mid-ocean ridges and get older away from them.
New crust is created at mid-ocean ridges, so rocks at the ridge are youngest; as seafloor spreads outward, older rocks lie farther away
Describe the processes and plate interactions that produced the Himalayas and why they are still growing.
The Indian Plate collides with the Eurasian Plate causing crustal shortening, folding, and uplift; ongoing convergence means the Himalayas continue to rise.
Explain how magma characteristics and dissolved gases control eruption explosiveness and the difference between lava flows and pyroclastic materials.
More viscous magma and higher dissolved-gas content increase explosiveness; lava flows are molten rock moving on the surface, pyroclastic materials are fragmented rock, ash, and tephra ejected explosively.
Explain why S-waves cannot travel through liquids and how that property helps scientists infer Earth's internal structure.
S-waves are transverse and cannot move through fluids; the inability of S-waves to travel through the outer core indicates it is liquid.
Contrast oceanic-oceanic convergence, oceanic-continental convergence, and continental-continental convergence — include the main geological outcome and one real-world example for each.
Oceanic-oceanic: older denser plate subducts forming volcanic island arcs (e.g., Japan); Oceanic-continental: oceanic subducts, forming continental volcanic arcs (e.g., Andes); Continental-continental: collision causes folding and uplift, forming folded mountain ranges (e.g., Himalayas).