Why don't volcanoes melt they got lava in them?

Answer 1

It's a matter of the energy needed. In order to melt the rock that makes it up, you have to heat it up to the melting point, and then provide additional energy to actually melt it. The amount of rock that makes up a volcano is larger than the amount of magma (underground molten rock) inside of it. The magma transfers heat into the surrounding rock and some of it can melt, but to do this, the magma itself must lose heat to do this, and the amount of energy, though large, is limited and the magma would cool and harden before it could melt a large portion of the surrounding rock. Additionally, rock is a poor conductor of heat. Rocks on the surface of the volcano will not be heated by magma hundreds to thousands of feet below. Furthermore, magma is not stored in the volcano itself, but in a magma chamber several thousand feet to several miles below it. When lava is erupted on the surface it loses heat to the air rather quickly, and cools before it can melt the surface rock.

Answer 2

It takes a lot of heat to heat rock up to its melting point and then melt it. Any heat that goes into that must be lost by the magma. Since the amount of heat is limited, a magma will usually solidify before melting too much of the surrounding rock. In many cases temperature-wise the magma is closer to solidifying than the surrounding rock is to melting. That said, it is not uncommon for magma within the earth to melt some of the surrounding rock. In most cases the amount of magma inside a volcano at any time is less than the amount of solid rock that makes up the volcano itself.

When it is erupted as lava it cools quickly as air carries heat away by convection. This does not give it much time to melt the rock it is erupted onto.

Answer 3

Volcanoes erupt molten rock called lava because the melting point of rocks in the Earth's mantle is lower at high pressures. The materials that make up a volcano, such as rock and ash, can withstand the high temperatures of the lava due to their composition and heat-resistant properties. This allows volcanoes to contain and channel lava without melting themselves.