This is a term from the German language that means “on top of ice” or “toward ice.” This type of ice forms when water emerges from the ground under freezing conditions — such as those in the Arctic. The water is often slightly above freezing, which is why it flows as a liquid. As soon as it hits extremely cold air, however, it turns into a solid. This ice forms a dam or wall. As more water comes out of the ground, it’s stopped by the frozen wall, until it rises over the top of the wall. This overflow then freezes into a new layer atop the first. This happens over and over again. By the time the weather is warm again, there may be aufeis several meters (yards) thick covering and surrounding a spring or river.
In a sentence
Very tall piles of aufeis may never fully melt during the high Arctic’s short summers.