The heat of summer causes substantial melting of ice on the surface of the glacier, which collects into small streams that flow down its face. The water itself of course melts more ice, carving the streams deeper and deeper over time, all part of the ever-changing nature of a glacier.

I saw a small avalanche on the ridge visible on the right here, a few moments after this image was taken. It was far away, and barely visible, but I still heard it a few seconds after it happened.