The Volcano is a location introduced in Monster Hunter 2, it is a lot larger than its Monster Hunter predecessor, the region is also far more harsh and inhospitable. You may be under contract on a quest during an eruption, tread lightly. In Monster Hunter Freedom Unite two extra areas can be explored, they are mainly for Lavasioth hunts.
Lava flowing in this region is dangerous to walk near, and it overflows at night time causing some changes in the layout.
You can find explosive rocks in some areas which will react to enough damage.
A shore, much like in the Jungle, instead of a tent your Base Camp has a Boat, there's two paths, one leading to Area 4 and the other to Area 1.
An open area surrounded by high ledges and a deep ravine in the bottom, during the day Apceros can be seen wandering around, while in the night the area may be filled with Bullfango and Ioprey, you don't need a Cold Drink here.
Another open area similar to the previous one, Bullfango, Melynx and Ceanataur are common here, you can see lava flowing on stone, near the entrance to Area 3, the other path leads to Area 10, you don't need a Cold Drink here.
A large open volcanic cave, during the night the rising lava makes this open area into a stretched zig-zag, you may see some Ceanataur, Vespoid or Apceros here, along with Large Monsters such as Rajang and Gravios.