It is normal. They begin popping up out of the ground as they bulb up. Usually about 2/3s of the onion will be sticking up out of the ground by the time it is mature and ready to pick.

thanks dawn. it seemed stange and soon they were all the way out of the ground.

You're welcome. Yes it is strange, but that's how they are. Normally it is not a problem, but if their foliage is burning up in high heat and isn't there above the bulbs to shade them, the onions can sunscald and be ruint.

Some people try to prevent this by planting the onions more deeply in future years, but the onions bulb up best and get larger if you don't plant them deeply. They like being planted shallowly.