They were formed over 21,000 years ago as the result of an underground steam explosion.

The reactor chamber's 2000-ton lid was lifted by the steam explosion.

The steam explosion resulting from such sudden corium-water contact can disperse the materials and form projectiles that may damage the containment vessel by impact.

Steam vents were reported active at the slide source for three years, leading to speculation that the event was started with a small steam explosion.

To date, the available pretreatment techniques include acid hydrolysis, steam explosion, ammonia fiber expansion, organosolve, sulfite pretreatment, alkaline wet oxidation and ozone pretreatment.