Final answer:
Magma plumes or hotspots create basaltic volcanoes when they encounter the oceanic crust. These hotspots generate heat that rises from the core-mantle boundary and causes the mantle and lithosphere to melt, forming magma that leads to volcanic island chains like Hawaii.
Step-by-step explanation:
When magma plumes, also known as hotspots, encounter the oceanic crust, they result in the creation of basaltic volcanoes. These hotspots are regions where heats originates from the core-mantle boundary and rises towards the surface. The intense heat and subsequent melting of both the mantle and the oceanic lithosphere above it produce magma. This magma then rises and erupts to form volcanic islands, such as those found in Hawaii.
Mantle plumes are not exclusively associated with any plate boundary, allowing for the possibility of hotspot-generated volcanic activity occurring anywhere on the Earth's surface. As the Earth's tectonic plates migrate over these stationary hotspots, the movement can lead to a chain of volcanoes that record the direction and speed of the plate's motion over time.