What is the primary cause of island formation at hotspots?

The primary cause of island formation at hotspots is the movement of lithosphere over magma sources. Hotspots are volcanic regions formed by the upwelling of hot mantle material that creates magma. As a tectonic plate moves over a stationary plume of hot material (the hotspot), the heat causes localized melting of the mantle, resulting in volcanic activity. This activity creates islands over time as lava accumulates and builds up above sea level.

For example, the Hawaiian Islands are a well-known hotspot volcanic chain. As the Pacific Plate moves northwestward over the Hawaiian hotspot, a series of islands and seamounts have formed sequentially over millions of years. This process demonstrates how the movement of the lithospheric plate facilitates the eruption of magma at the surface, leading to the formation of islands.

The other options do not primarily account for island formation at hotspots: subduction involves the descent of one tectonic plate under another and typically leads to volcanic arcs rather than hotspot islands; melting of continental crust is more associated with continental collision rather than hotspot activity; and collisions of tectonic plates refer to convergent boundaries, which do not create hotspots but rather lead to different volcanic and geological features.