How do hotspots differ from plate boundary volcanism?

• A. Hotspots occur at subduction zones.
• B. Hotspots are fixed mantle plumes that create volcanoes as plates move over them; volcanism occurs away from plate boundaries.
• C. Hotspots generate earthquakes rather than volcanism.
• D. Hotspots are caused by atmospheric conditions.

Answer: (B)

Hotspots come from relatively fixed plumes of hot material rising from deep in the mantle. The plume stays in roughly the same place while the tectonic plate above it moves. As the plate passes over the plume, magma melts and feeds volcanoes. This creates a chain of volcanoes that sits away from plate boundaries, and the new volcanic activity appears where the plate is currently over the plume. Over time, the older volcanoes move away from the hotspot, so you often see a line of volcanic centers with ages that get older farther from the current hotspot location. A classic example is the Hawaii–Emperor seamount chain, where the islands get progressively older with distance from Hawaii.

Plate boundary volcanism, by contrast, happens at the edges where plates interact—subduction zones melt mantle due to water and pressure, and mid-ocean ridges pull plates apart, causing magma to rise. This means volcanism is concentrated at plate boundaries, and such regions often experience strong seismic activity as well.

So the key idea is that hotspots are fixed mantle plumes forcing volcanoes as plates move over them, producing volcanism away from boundaries, unlike boundary-driven volcanism.