How to make volcanoes

craters are a good choice if you don't wanna modify existing terrain
simple rearrange the crater curve, make sure the "peak" is at value 1 and location around 0.2 to 0.5, the volcano's pit is between value -1 and 0.5ish, and the bottom is at 0

make water lava
then set the height to where it won't get drowned in lava
then the volcano part
Make a mountain
make a deep hole in it (enough to get to the lava)
tada, you have lava like that pink moon that orbits tydos that I forgot the name of