You can disable it (and also explosions) in the cfg.. As a side note.. You are in the freaking nether. Why do people expect the nether to be a piece of cake? Its supposed to be hell or something like that, and its already easy enough, some spice to it doesn't harm in any way, in fact, i find myself in the nether a lot usually because i feel its better than the overworld if you really want to have a challenge (which isn't like playing warhammer 40k soulstorm in max difficulty, but still kind of challenging) so yeah.. Also nether ores are worth the danger, they duplicate your output once more (And if you use mimichite.. hell yeah, 4 ores each nether ore) so.. Use silk touch, change cfg, or dont mine them