question: What substance, which forms igneous rock, flows out in rivers of lava when it reaches the surface?
distractor3: fertilizer
distractor1: granite
distractor2: soil
correct_answer: magma
support: The chemistry of a magma determines the type of igneous rock it forms. The chemistry also determines how the magma moves. Thicker magmas tend to stay below the surface or erupt explosively. When magma is fluid and runny, it often reaches the surface by flowing out in rivers of lava.