First defined in NASIOC's Off Topic forum by Kaiser as the slow, crampy, painful, and excruciatingly long build-up of poo in one's bowels, which finally reaches a breaking point and results in a massive avalanche of crap being explosively expelled from one's ass. Hence, assalanche.
Zeke sat miserably on the toilet for 30 mins with bad stomach cramps -- a half hour cycle of cramping and loosening and cramping and loosening tearing at his abdomen. But, frustratingly, no poo was shat. He suffered wave after wave of pain...until, finally, that last little snowflake fluttered down on 500 billion tons of brown snow. The assalanche came without warning, and it was fierce. Many people in Toiletville were caught unaware and perished in a 100mph rush of furious poo.