Building on permafrost is difficult because heat from the structure can thaw the permafrost. Snow that falls in winter accumulates on the ground until the spring thaw. The spring thaw also proceeds gradually northward. It may be caused by intense rainfall, thaw or flood. The Ainu usually hunted bear during the spring thaw. The Khrushchev Thaw () brought some fresh wind to literature. During the spring thaw, Germany and Central Europe reported severe flood damage. The lack of a proper spring and summer thaw kept the ship at bay. They return to the cryo-prison and begin to thaw out more convicts. "Synchrony of Discharge with Spring Thaw&colon;" The Red River flows northward. They thaw him out and are surprised to find that he can speak. Yevtushenko was one of the authors politically active during the Khrushchev Thaw. As vice president, Biden supported Obama's Cuban thaw and reestablishment of diplomatic relations with Cuba. Following the Khrushchev Thaw, censorship was diminished. Thaw and Evelyn continued their travel through Europe.