Social Sciences and History / Unit 10 SSH 0922 worked example, 60 to 90 seconds
Reading a Boundary From Its Landforms
The idea
The exam describes a landscape and asks which plate boundary made it, and Dastrup's three categories, joined to its chapter on structures, give the reading. Convergent boundaries, plates moving toward each other, produce compressional stress, thickening: mountain ranges, deep trenches where one plate descends, explosive volcanoes, and reverse faults where the hanging wall rises. Divergent boundaries, plates moving apart, produce tensional stress, stretching and thinning: mid-ocean ridges, rift valleys, new crust, and normal faults where the hanging wall drops. Transform boundaries, plates sliding past each other, produce shear stress: strike-slip faults with horizontal motion, frequent earthquakes, and little volcanism. Active margins host the first and third; passive margins, none.
In practice
Given "a trench offshore, volcanoes inland, thick crust", convergent. Given "a long ridge with a central valley and fresh basalt", divergent. Given "a straight fault along which the two sides have moved sideways for miles, with earthquakes and no volcanoes", transform. Given "a mountain chain of folded rock with reverse faults", convergent, continent against continent. Ask which stress the rocks record: squeezed, stretched, or sheared.
Where people slip
The trap is expecting volcanoes at every boundary; transform boundaries have few. The second trap is the fault names: reverse for compression, normal for tension, strike-slip for shear, the anchor's three.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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