Survival

Briefly about Survival manga:

 After a terrible earthquake, Satoru wakes up in a pitch black cave. The cave had collapsed during the quake, trapping him and his friends inside. Desperately trying to find a way out, he searches through the rubble with only his backpack on. But as he crawls down an unfamiliar tunnel, Satoru discovers something unbelievable: Japan has sunk underwater due to the earthquake and he is stranded on an island with no one to help him! Can Satoru learn how to survive by himself?