Question about the tomb (Assassin's Creed: Odyssey)

Started to play this wonderful game,but faced with one problem.Almost in each grave there are stones or that there (screenshot) and behind them the chest,but to break the stone? bypass like not found.
And even on the same island,given the task of killing a monster,(there are still a number of fisherman was asked to save his brother,and when you come into the cave and run to the chest 1,the floor collapses) so there is generally a stone wall is cracked,constricted Board,tried to burn - out,strikes do not help,there should be some sort of explosion,but there is no such abilities.How to get this?