Shit volcano 

May be used to describe a person or object that spews out excesses of crap in verbal or physical form.

Word derives from a combination of the relatively harmless cuss shit and volcano; which until just recently wasn't considered quite as negative a word as it currently is (post Icelandic volcano ash cloud malarkey).

Carl is such a shit volcano.

Shit volcano by Shitvafjökul July 7, 2010

shit bubble volcano 

The act of packing an anus with baking soda then topping off with vinegar to create a shitty, bubbly anal volcano. (Mentos and diet coke can be substituted but with somewhat less spectacular results)

I heard Mark and Brian tried a shit bubble volcano last night, I feel bad for those casino cleaners.

shit bubble volcano by BrainGear October 6, 2017

Volcanic Shit 

When you're constipated and a fart builds up above the stuck shut, creating more and more pressure. The end result is a painful explosion of shit scattered around your toilet basin.

Argh, my ass hurts so much after that Volcanic Shit I had.

Volcanic Shit by Archaeon December 29, 2012