Earth Science: Plate Boundaries: Convergent, Divergent, Transform
Identifying plate interactions and the landforms they create
Earth Science: Plate Boundaries: Convergent, Divergent, Transform
Identifying plate interactions and the landforms they create
Earth Science - Grade 9-12
- 1
Define the three main types of plate boundaries: convergent, divergent, and transform. Include the direction of plate motion for each type.
Focus on how the plates move relative to one another.
At a convergent boundary, two plates move toward each other. At a divergent boundary, two plates move away from each other. At a transform boundary, two plates slide horizontally past each other. - 2
At a mid-ocean ridge, magma rises and cools to form new oceanic crust. What type of plate boundary is this, and why?
A mid-ocean ridge is a divergent boundary because two oceanic plates are moving apart and new crust forms as magma rises and solidifies. - 3
The Andes Mountains formed where the oceanic Nazca Plate moves beneath the continental South American Plate. Identify the type of boundary and explain why volcanoes form there.
Think about which plate is denser and what happens when it sinks into the mantle.
This is an oceanic-continental convergent boundary. Volcanoes form because the denser oceanic plate subducts, water from the subducting plate helps melt mantle material, and magma rises through the continental crust. - 4
The San Andreas Fault in California is a place where the Pacific Plate and North American Plate slide past each other. What type of boundary is this, and what major hazard is most common there?
The San Andreas Fault is a transform boundary. The major hazard most common there is earthquakes caused by stress building up and releasing as the plates slide past each other. - 5
Compare oceanic-continental convergence with continental-continental convergence. Describe one major geologic feature produced by each.
Oceanic crust is denser than continental crust.
Oceanic-continental convergence usually produces a subduction zone, a deep ocean trench, and a volcanic mountain range on the continent. Continental-continental convergence produces large folded mountain ranges because both plates are too buoyant to subduct easily. - 6
A geologist finds a deep ocean trench next to a chain of volcanic islands. Which type of plate boundary is most likely present? Explain your reasoning.
The most likely boundary is an oceanic-oceanic convergent boundary. One oceanic plate is subducting beneath another, forming a trench, and magma rises to create a volcanic island arc. - 7
Explain why the youngest oceanic crust is usually found near mid-ocean ridges and older oceanic crust is found farther away.
Connect crust age to where new crust is created.
The youngest oceanic crust is found near mid-ocean ridges because new crust forms there as magma cools. As seafloor spreading continues, older crust is pushed farther away from the ridge. - 8
Two plates move toward each other, but neither plate subducts deeply because both are made of continental crust. What type of boundary is this, and what landform is likely to form?
This is a continental-continental convergent boundary. A large mountain range is likely to form as the crust compresses, folds, thickens, and uplifts. - 9
A student says, "Transform boundaries do not create or destroy crust, so they are not dangerous." Evaluate this statement using evidence from plate tectonics.
Think about what happens when sliding plates get stuck and then suddenly move.
The statement is incorrect because transform boundaries can be very dangerous even though they do not create or destroy crust. Plates can lock due to friction, stress can build, and sudden movement can produce strong earthquakes. - 10
Use the following observations to identify the boundary type: shallow earthquakes, a central rift valley, high heat flow, and basaltic lava. Explain your answer.
The boundary is divergent. Plates are pulling apart, which creates a rift valley, allows hot mantle material and basaltic magma to rise, and causes shallow earthquakes as the crust stretches and breaks. - 11
Rank these boundaries from most likely to produce explosive volcanoes to least likely: transform boundary, oceanic-continental convergent boundary, divergent boundary. Explain your ranking.
Explosive eruptions are often linked to subduction zones and viscous, gas-rich magma.
The oceanic-continental convergent boundary is most likely to produce explosive volcanoes because subduction can generate gas-rich, silica-rich magma. A divergent boundary is less likely to produce explosive volcanoes because basaltic lava is usually runnier. A transform boundary is least likely because it usually does not produce magma. - 12
A plate boundary has frequent earthquakes at depths ranging from shallow to very deep, with the deepest earthquakes located farther inland from an ocean trench. What type of boundary is this, and what does the earthquake pattern show?
Deep earthquakes usually indicate a plate sinking below another plate.
This is a convergent boundary with subduction. The pattern shows a dipping zone of earthquakes, called a Wadati-Benioff zone, where the subducting plate descends into the mantle.