Question

an extrusive igneous rock could form in which of the following scenarios?
o a an effusive volcanic eruption leaves a thin layer of lava on the slope of a volcano.
o b continental crust 3000 meters under a large mountain range is altered by temperature and pressure.
o c sediment carried by a river is buried in a delta and undergoes lithification.
o d a large magma chamber cools slowly 200 meters below earths surface.

Explanation:

• Extrusive igneous rocks form from lava that cools quickly on the Earth's surface.
• Option a describes an effusive volcanic eruption (lava flow) on the volcano slope (surface), which is where extrusive igneous rocks form.
• Option b: Alteration of continental crust by temperature and pressure forms metamorphic rocks.
• Option c: Lithification of sediment forms sedimentary rocks.
• Option d: Slow - cooling magma (200 meters below surface, still intrusive environment) forms intrusive igneous rocks.

Answer:

a. An effusive volcanic eruption leaves a thin layer of lava on the slope of a volcano.