Volcanoes are a naturally generated part of the world introduced by RedPower 2. They're made of Basalt and take the form of either large, narrow mountains, reminiscent of stratovolcanoes, or short, flat mountains, reminiscent of shield volcanoes.
Volcanoes often, but not always, spawn with a magma chamber in the center of them, a 1x1 shaft of lava that leads down to a lava pool near Bedrock. Lava often flows down to ground level, where it can start forest fires or form stone over nearby water. It is possible that a volcano can contain no visible lava at all.
Volcanoes spawn after the world initially generates, which can cause floating blocks and random drops to appear along the volcano's surface.