noun
permafrost
Technical term for ground that remains frozen for at least two consecutive years. Common in environmental and geological contexts.
シベリアの永久凍土が溶け始めている。
The permafrost in Siberia is starting to thaw.
凍土 means 'frozen soil' in general, while 永久凍土 specifically refers to permafrost that stays frozen year-round.
Compound of 永久 (eternal) and 凍土 (frozen soil). The term is a direct translation of the English 'permafrost'.