The volcano is a stage that is full of lava. The floor is made of ash, and the only danger is the lava. The lava does not burn the player, but does increase fuel consumption by a lot. Most players will find themselves out of fuel when going up a steep hill after the pool if they are not careful. For a while at the start, the ground is relatively level, compared to other levels. After that, the hills are like a lot of basic stages (such as highway, or countryside), but the lava pools tend to be right in front of the hills that are steep, to try to get you out of fuel before you make it to the top.
Like the water on Beach and mud on Mudpool, the lava will slow most vehicles down. The hovercraft is good on this stage as it will make sure you spend as little time as possible in the lava. The moonlander can be good too, as well as the rally car as it can stunt over the lava pools. Vehicles that have fuel upgrades are not recommended, as the lava means that they will run out of fuel very fast, even if the fuel upgrade is on a high level.
Overall, this stage is very split, where the vehicles are either very good or very bad at this level. More skilled players may be suited to this level, because of the lava, and also because of the fairly gentle slopes compared to other levels, making for some easy high score attempts.