From the moment the boys land on the island, we begin to see signs of destruction. Over and over we are told of the "scar" that the plane leaves in the greenery (1.3). The water they bathe in is "warmer than blood" (1). The boys leave "gashes" in the trees when they travel (1). The lightning is a "blue-white scar" and the thunder "the blow of a gigantic whip," later a "sulphurous explosion" (9).
If you're trying to answer the big question of whether the boys are violent by nature or are made violent by their unfortunate situation, you could argue that (1) because the island/nature is already so violent (think the thunder and lightning), the boys couldn't help but become part of its savagery when they arrived; or that (2) the boys are bringers of destruction, ruining the island paradise.
Us? We'd like to go with option 1, but we're pretty sure Golding wants us to pick option 2.