Police said the boy apparently slipped after he breached a fence surrounding the prohibited area at the Solfatara Crater in Pozzuoli. A 7-year-old boy who was a member of the same Italian family was nearby but remained outside the fenced-off area.
It wasn't immediately clear if the 11-year-old and his parents were overcome by gases or were killed as the result of an explosion of super-heated mud. Heavy rains in recent days may have played a role by creating more openings in the volcanic field's surface.
The fields are scorching hot only a few inches below the surface.
Signs around the crater in multiple languages warn of the danger of burning from high soil temperatures and steam up to 160 degrees Celsius (320 degrees Fahrenheit.)
Visitors are told to stay clear of fumaroles, openings in the Earth's crust that emit steam and gases, and not to climb the slopes or breach the fences.
While the Phlegraean Fields are privately run, geologists monitor the area round the clock, checking temperatures and chemically analyzing gases. They have determined that the fields rose by about 30 centimeters (12 inches) over a decade.
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