What causes floor tile to buckle?

Moisture,expansion of the underlayment/settling of the home,subfloor nails popping up,glue or adhesive not properly applied/area not prepared well enough upon installation.

Depending on the age of the tile will determine what is underneath it, usually it's a installatino prep problem, either tile mortared to plywood, or the sub floor wasn't fastened down enough. Thinset was mixed with too much water, it doesn't take a lot of movement to crack a tile.

Both responders are correct, I have to spread some around before I can give KBC another greenie. Is this tile ceramic or vinyl?

It could be any of a number of things How old is the tile in question? If it is fairly old then it is probably due to continual changes in temperature and humidity that occur as the seasons change with each passing year. If it is relatively new then it could be improper installation, probably failure to properly prep the subfloor.

The tile in question was installed more than twelve years ago,and is only happening in area.