Io is the fourth-largest moon in the Solar System and with over 400 active volcanoes, Io is also the most volcanically active body in the Solar System. Volcanic plumes rise up to 300 km above its surface.
Io's volcanic plumes and lava flows cover the surface in yellow, red, white, black, and green compounds of sulfur. Io's surface is also dotted with more than 100 mountains, with some of them taller than Mount Everest.
Due to its varying distances from Jupiter, Io is subjected to tremendous tidal forces. These forces cause Io's surface to bulge up and down by as much as 100m. They also generate a huge amount of heat within Io, keeping much of its subsurface crust in liquid form.
Io's orbit cuts across Jupiter's magnetic field lines, turning the moon into a powerful electric generator. The electric current of 3 million amperes takes path to Jupiter's surface, creating lightnings in its upper atmosphere.