Why did my dog randomly start eating gr?

The other night, my dog started making noises like he was about to throw up. To prevent him from doing this in the house, we let him outside. Instead of throwing up, he began to obsessively eat as much snow as he could. This has also happened about two other times, in the summer, with gr. When we let him inside, he begins licking the floor, and eating any small objects he can find, inclusing wood chips from near the fireplace, and small pieces of plastic. He does this obsessively too, and all but ignores us when we call him or pet him. We had to put him in his crate to prevent him from eating anything that could be dangerous to him! Does anyone know why he is doing this and if we should be worried? Thanks!