True colours

" Please start meditating here," Mo Xifeng pointed to the deep chasm which was filled with crater-like holes as she looked at Mo Qiang and asked her to go down and start meditating. The latter looked at the chasm which was made up of blood-red stones with glowing craters spread all over the place, one could see that inside those craters there was frothing magma boiling. The temperature of the chasm was worriedly hot and scalding but that was not all, in every fifteenth minute, the crater would explode and then a big boulder the size of an ostrich egg would be sent flying out of each crater at repeated intervals. 

And once the boulder was to come out of the crater, under the lowering pressure and heat, it will explode because of the high pressure that was inside it causing an unbalance which led to an explosive reaction.