It might be possible to melt concrete if lava in contact with it was hot enough. But it is more likely that concrete would decompose and become "crumbly" before it "melted" when heated.
The melted rock coming from a volcano is called lava.
Lava.
"lava"
If it reaches the surface, it is magma or lava. If it merely intrudes into rocks already formed, it is intrusive. Such as sills and dikes.
lava
The melted rock coming from a volcano is called lava.
Lava.
Lava
"lava"
Chocolate lava is just melted chocolate.
If it reaches the surface, it is magma or lava. If it merely intrudes into rocks already formed, it is intrusive. Such as sills and dikes.
Lava is melted rock, it is quite viscous.
Lava.
lava
Lava.
lava
Lava.