A fissure is a crack in a rocks. A volcanic fissure is one from
which lava erupts.
Fold mountains are a type of mountain range that is formed when two
collide (or one continental plate colliding with an oceanic plate).
The colliding crust is compressed and pushed upwards (uplifted),
forming mountains. For example, the Himalayas were slowly formed
when the Indian plate collided with the Asia-European plate millions
of years ago.