Questions: Plate Boundaries

Question 1

At which type of plate boundary is new oceanic crust being created?

• A. Convergent boundary
• B. Transform boundary
• C. Divergent boundary
• D. No new crust is ever created — Earth has always had the same crust

Answer: (C)

At divergent boundaries, plates move apart and magma rises from the mantle to fill the gap, cooling and solidifying into new oceanic crust. This process is called seafloor spreading. The Mid-Atlantic Ridge is a famous example — it is literally building new ocean floor as the Americas and Europe/Africa move apart.

Question 2

Why do most earthquakes and volcanoes occur along plate boundaries rather than in the middle of plates?

Model answer: Plate boundaries are where plates interact — pushing together, pulling apart, or grinding past each other. These interactions create the forces that trigger earthquakes (sudden releases of built-up stress) and volcanoes (magma rising through cracks and weak zones). The interiors of plates are relatively stable because they are far from these zones of interaction.

When you plot earthquake and volcano locations on a map, they clearly outline the plate boundaries, especially the Ring of Fire around the Pacific. This pattern was one of the key pieces of evidence that led to the acceptance of plate tectonics theory.

Question 3

The San Andreas Fault in California is a transform boundary where two plates slide past each other.

• T. True
• F. False

Answer: True

The San Andreas Fault is where the Pacific Plate and the North American Plate slide horizontally past each other. This is a transform boundary. The plates are not creating or destroying crust — they are grinding sideways, which produces earthquakes but generally not volcanoes.