Glacial Rivers Wild and silty rivers run from the park's glaciers to its coastlines. These rivers look different and act different than most rivers. Icy cold temperatures, fluctuating levels, changing channels and heavy loads of silt and rock can challenge hikers, boaters and anglers. Wide Rocky Beds and Braids Moving glacial ice scours chunks of bedrock and fine rock flour from the mountainsides. These chunks and bits of rock are mixed into glacier ice and then released in its meltwaters.
Large rocks drop out of the stream flow immediately.
Smaller ones roll away downstream where they lodge in the river's channels, filling them and eventually diverting the river to a new course. Glacial rivers are constantly shifting from one channel to another, forming many braids in a wide rocky bed. These uneven shifting rocks can be difficult for a hiker to negotiate. Silty Water Fine rock flour washes downstream with the glacier's meltwater. In Chugach the dominant rock is graywacke which colors the streams a muddy gray-brown.