ENV 100 Chap.3 Plate Tectonics and Global Impacts
Plate Tectonics and Global Impacts
This chapter compares divergent, convergent, and transform boundaries through relative motion, landforms, earthquake depth, volcanism, and ocean-basin structure. New Zealand examples connect plate geometry with hazards, while mountains, gateways, weathering, and eruptions extend tectonic effects into climate. Evidence comes before the boundary label.
What this chapter covers
- 01
Plate motion and mantle context
- 02
Divergent ridges and rifts
- 03
Subduction and volcanic arcs
- 04
Transform faults
- 05
Earthquake depth patterns
- 06
Mountains, oceans, and climate
Worked example · free
Infer subduction from a mapped pattern
- +1Use the trench to locate plate bending.
- +1Use the dipping earthquake zone to trace the slab.
- +1Place the arc on the overriding plate.
- +1Link slab fluids to melt generation.
Key terms
- Subduction
- Subduction is the descent of one plate beneath another at a convergent margin.
- Epicentre
- The epicentre is the point on Earth's surface directly above an earthquake hypocentre.
- Volcanic arc
- A volcanic arc is a chain of volcanoes on the overriding plate above a subduction system.
- Transform boundary
- A transform boundary accommodates lateral motion between adjacent plates.
- Hot spot
- A hot spot is a region of volcanism that can occur away from a plate boundary.
Plate Tectonics and Global Impacts FAQ
How does earthquake depth identify a boundary?
Shallow earthquakes occur in several settings, but a landward-deepening plane of hypocentres is strong evidence for a descending slab. It should be checked against trenches, motion vectors, and volcanic position.
Are volcanoes always on plate boundaries?
Many form at subduction zones or rifts, but hot-spot volcanism provides a clear counterexample. Location, age progression, chemistry, and plate motion help distinguish the settings.
How can tectonics affect climate?
Mountain building changes rainfall and weathering, volcanic material can alter atmospheric conditions, and opening or closing ocean gateways reorganises circulation. Each link operates over a particular spatial and temporal scale.
What distinguishes epicentre and hypocentre?
The hypocentre is the rupture location at depth, while the epicentre lies directly above it at the surface. Mapping many hypocentres reveals three-dimensional fault or slab geometry; plotting epicentres alone preserves location but loses that crucial depth pattern.
Why is a trench not enough?
A trench is consistent with plate bending, but a robust subduction interpretation also uses earthquake depths, plate-motion direction, fault geometry, and volcanic-arc position. Several observations must form the expected spatial sequence before the full plate model is preferred.
Assessment move
Start every revision session by drawing divergent, convergent, and transform boundaries without labels. Add motion arrows first, then the structures that follow from those motions: ridge or rift, trench and descending slab, collision belt, or lateral fault. Only after the geometry is clear should you add crust creation, destruction, or conservation.
Build a comparison table using the same criteria for every boundary: relative motion, typical topography, earthquake depth, volcanism, crustal effect, and one limitation or counterexample. This makes it harder to confuse a hazard with a boundary definition. For map practice, use a fixed sequence. Locate the major features, compare earthquake depths, infer the geometry, connect the mechanism, and state the uncertainty.
Trace a hypothetical transect from ocean basin across trench to arc and explain why hypocentres deepen in one direction. Repeat the transect for a transform fault and a ridge to see which observations disappear. Use New Zealand examples to test the reasoning, but never let a place name replace the process. If a question mentions a tsunami, earthquake, or eruption, first identify the motion and geometry capable of producing it.
Add hot spots as a deliberate counterexample to the claim that all volcanism lies on a boundary. For global impacts, create separate chains from mountain building to rainfall and weathering, from ocean-gateway change to circulation, and from eruptions to atmospheric effects. Attach a time scale to each chain.
Retrieval practice should mix diagrams and prose: sketch for three minutes, write a six-sentence explanation, then check whether the text describes every arrow. When comparing two interpretations, name the observation that would discriminate between them, such as earthquake depth, age progression, focal mechanism, or plate-motion direction.
Before an in-class test, rehearse one labelled boundary diagram within the likely short response time. Your final audit asks four questions: Did I state motion? Did I place the overriding and descending plates correctly? Did I use evidence rather than circular labels? Did I distinguish the tectonic setting from its possible hazards?
