What geologic structure is formed from molten rock that erupts?

A volcano is the correct answer because it specifically refers to a geologic structure that forms when molten rock, known as magma, is expelled from the Earth's interior through openings in the crust. When this magma reaches the surface and erupts, it may solidify into various forms, building up a cone-shaped feature characteristic of volcanoes. This process can involve not only lava flows but also ash and gas emissions, resulting in various types of volcanic activity.

In contrast, a plateau is a flat, elevated landform that does not involve volcanic activity. A caldera is a large depression formed when a volcano erupts and collapses; it is specifically a feature of specific volcanic events but does not represent the structure formed during an eruption. A mountain range, on the other hand, is created through tectonic processes such as uplift and folding of the Earth's crust and does not directly result from volcanic activity. Hence, a volcano is the most accurate definition of the structure formed from the eruption of molten rock.