Other answers

Volcanic Chimney is a tube that connects the magma chamber of some volcanoes, located in the deep, with the surface. This duct often grows as eruptions go ejecting lava, They can be extended to 200 km deep.

There is a lot of heat within the earth, this heat is to partially melt rocks in the upper mantle, about 50-100 km below the surface.

It depends on how close you are, what kind of lava flow it is, and whether you are upwind or downwind.
When Hawaii lavas erupt, they are around 1170 to 1175 degrees centigrade. Other volcanoes produce cooler more viscous lavas in the 700C. Still much hotter than in your oven when a turkey is baking!

I have taken the information from:

Wikipedia

Volcano World