An ice dam, is when the snow on the roof melts at the lower edge, then forms ice as it refreezes. It prevents the melt from getting to the gutter, and more and more ice builds up.
The issue is, as the melt continues the water has to go somewhere....it will find a place to go, but nowhere good. I had my wood floor buckle a few years back after a major storm.. Fortunately the floor flattened as it dried.
There are many reasons these dams form. Maybe a poor angle. Or, If you don't have proper insulation, and it creates hot spots on the roof, which melts snow, and then the ice begins etc.
Add to this, more snow storms, and you have big issues. It's been snowing every other day here.
That's basically an ice dam. I use a roof rake to get the snow cleared from the gutter, but it ain't easy. I did it today, and there is ice forming already. Argggg!
The battle continues.