ASHFORD, Wash. (AP) — Staff at Mount Rainier National Park are warning visitors to watch out for crevasses on the popular Muir snowfield.

They say the crevasses are opening up as the snow continues to melt, and they can be deep enough to cause injury or make it difficult for anyone to hear you calling for help.

The main boot track typically avoids crevasses, but some of the glissade paths down the snowfield might not. Rangers say they crevasses are not marked and visitors need to be careful.