Soliton explosions are among the most intriguing nonlinear dynamics in dissipative systems, manifesting themselves as a self-recovered localized structure when suffering explosive instabilities. Herein, we report on the investigation of soliton explosions in an ultrafast fiber laser operating in the multi-soliton regime. It is demonstrated that explosion of one soliton could be induced by another one through the soliton interactions mediated by the transient gain response of an erbium-doped fiber. We denote this phenomenon as "mutually ignited soliton explosions" when referring to the multi-soliton regime. The results provide the first investigation of soliton explosions in the multi-soliton regime and, therefore, will enhance a more comprehensive understanding of the soliton exploding phenomenon.