Siberia

Siberia is a region of the Southern Oval that is often described as a frozen wasteland. However, the planet's geological activity has made it play a key role in ending Nuclear Winter by the means of a uranium flood basalt eruption.

Siberian Traps
Siberia was noted for causing many flood basalt eruptions, which had led to the extinctions of many inhabitants of the land before human civilization. A flood basalt eruption is when a plumage of the Earth's mantle rises up to the crust & turns the land into a sea of lava.

Uranium ore
Over time between the last flood basalt eruption & the beginning of Nuclear Summer, a giant amount of rock & crystals compressed into tiny radioactive crystals of uranium. One crystal could have the power to run every building in Wildwood with every appliance turned on for a whole year.

Nuclear Thawing
In 85Y, a nuclear bomb test had gone awry as the mushroom clouds had spewed nuclear isotopes into the upper atmosphere. The rising of these chemicals took about 3-5 years to reach the greenhouse gases & ozone layer. Once up there, the isotopes caused the greenhouse gases to accelerate, generating a 5 year period of never-ending summer, from 90-95Y. The year summer ended, the greenhouse gases broke apart & the Earth cooled dramatically. This caused 5 years of winter. The winter appeared to end in 100Y when a flood basalt eruption in Siberia began. However, the uranium ore stood between the lava & the surface & the uranium was forced out of the ground, generating radiation that produced more greenhouse gases & warmed the Earth to the point that the natural balance was restored.