When a volcano erupts, what is the hot, liquid rock with a massive volume called?

When a volcano erupts, the hot, liquid rock that comes out with massive volume is called lava.

Explanation:

Inside the Earth, beneath the crust, there are extremely hot molten rocks. This molten material is called magma.

Magma is stored in magma chambers deep under the Earth’s surface. It contains melted rock, gases, and sometimes crystals.

When pressure builds up, magma rises through cracks in the Earth’s crust and erupts through a volcano.

Once magma reaches the surface and flows out, it is called lava.

 In short:

Magma = molten rock beneath the Earth’s surface.

Lava = molten rock that comes out during a volcanic eruption.

Because lava flows out in huge amounts and spreads over a wide area, it is referred to as hot, liquid rock with a massive volume.

Final Answer: Lava – the hot, liquid rock that erupts from a volcano.