Volcanic Eruptions are a type of geological natural disaster that occur when lava pushes its way to the surface and when the Earth's crust's tectonic fault lines move and shift. Volcanic eruptions are considered to be very dangerous, due to releasing hot ash, lava, lahars, pyroclastic flows and even raining soft volcanic ash. They occur on mountains and in calderas.
When the Earth's core was heated up so high, due to a massive solar flare, the crust became unstable and it caused the world to come to an end in 2012. Lava began to force its way to the surface as volcanic activity began to increase, due to the core being heated up so high. When the apocalypse occurred, numerous volcanoes erupted all around the world, including supervolcanoes, which destroyed and engulfed many regions around the globe. The pyroclastic flows killed thousands as ash rained everywhere.
After the apocalypse ended and time was reset to year one, the volcanoes became dormant again, but it is presumed that due to the constant volcanic eruptions, it would cause a volcanic winter to occur.