Are there are sometimes flowing rivers within a glacier?

Yes, there are sometimes flowing rivers within a glacier. These rivers are called subglacial rivers, and they flow beneath the surface of the glacier. They are formed when meltwater from the surface of the glacier seeps into cracks and crevasses and then begins to flow downhill. Subglacial rivers can be very powerful, and they can carry large amounts of sediment and debris. They can also be very dangerous, as they can suddenly burst through the surface of the glacier, creating flash floods.