A number of people have asked recently what an ice stream is. I have put in various posts before on this topic -- I suggest you do a search via the search box. An ice stream is simply a stream of ice within an ice cap or ice sheet which is moving more rapidly than the surrounding ice. That may be because there is a rock trough below and a large input of ice from further up-glacier; there may then be ice melting on the bed and a subsequent acceleration in ice velocity.
"Streamlines" are simply the recreated ice flow directions, conventionally shown by arrows. Note that you can also recreate streamlines for ice flow in areas affected by an ice cover, even though you are not dealing with an area covered by an ice stream.
An ice stream may be highly crevassed -- and there is often another crevassed zone on the flanks of the ice stream where sluggish flanking ice is literally ripped apart.
Within the ice stream ice movement directions (and hence directions of erratic transport) will be rather consistent. In the intervening areas (which are sometimes "ice shed" areas) ice movement directions may be highly eccentric and variable. High rates of ice evacuation in an ice stream will lower the ice surface there, and cause ice from the intervening areas to flow towards the ice stream. If the ice stream slows down, or if accumulation patterns vary, ice movement directions may literally be reversed in these zones. Erratic movements in these areas will be very erratic indeed.......
The Irish Sea Glacier must have been an ice stream, flanked by ice-covered terrain on either side. There must also have been big ice streams in the Moray Firth region and in the Firth of Forth. This is the BRITICE recreation for 23,000 years ago -- in the Devensian Glaciation: