Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Some volcanoes form over active hot spots . Scientists count about 50 hot spots on the Earth. Hot spots may be in the middle of a tectonic plate. Hot spots lie directly above a column of hot rock called a mantle plume . Mantle plumes continuously bring magma up from the mantle towards the crust ( Figure below ). Answer: magma
Output:
What substance comes toward earth's crust through mantle plumes?