spontaneous

–adjective
1. coming or resulting from a natural impulse or tendency; without effort or premeditation; natural and unconstrained; unplanned: a spontaneous burst of applause.
2. (of a person) given to acting upon sudden impulses.
3. (of natural phenomena) arising from internal forces or causes; independent of external agencies; self-acting.
4. growing naturally or without cultivation, as plants and fruits; indigenous.
5. produced by natural process.