The big blue is a drug-related tragedy that took place in Moria. The well known dwarf cyclo the fair bearded mixed the hazardous red mushroom with lapiz lazuli, going into a week long delirium which ended in this room.
After this incident, the fair bearded insisted that “every” column in Moria was blue, made from the lapis despite the fact that only two rooms in Moria actually contains such columns (including big blue). To this day, he still has the blues.