Three members of a family have died after falling into a volcanic crater in Italy, according to news reports.

The family of four from northeastern Italy was on vacation in Pozzuoli, viewing the sulfurous Solfatara crater. Their 11-year-old son ran through a safety barrier and went onto an unstable portion of the crater that is made of crumbling quicksand.

The boy's mother and father rushed to save him and caused the crater to collapse, forming a small hole. All three dropped into the hole, fell unconscious and died, likely by inhaling the noxious fumes, the BBC reported. The couple's other son, who is 7 years old, stayed put and survived. Rescue workers did manage to retrieve the bodies and reported that the pit was filled with boiling mud.

The Solfatara crater is one of many now-dormant volcanoes in a field of volcanic activity west of Naples. It formed about 4,000 years ago but last erupted in 1198, the BBC reported. Despite being dormant, Solfatara still emits sulfur and steam, and is a popular tourist attraction.

Originally published on Live Science.