听力题 W: It''s good to see you back. How was your trip to Canada? You went to the Rockies, didn''t you? M: Well, word does get around, doesn''t it? Yeah, it was great. The place has a kind of "European-Alps-village" charm to it, but at the same time it has some great day hikes. Want to see some pictures? W: Sure, I see what you mean. The background mountains are quite something. Wait... don''t tell me you actually went on the cable car ride. That''s quite a height! I thought you said these things frightened the daylights out of you— and... here you are. M: Yeah, what''s interesting about this canyon is that it was basically the result of the Ice Age retreat in a small stream eating its way for many years down a valley. That glacier is something else. W: I still don''t understand why it doesn''t melt during the summer. It can''t be that cold. M: Well, we are up about 5,500 feet there, but glaciers by nature melt only about a few inches a year. The density of the sheets is the main reason. Besides that, they are protected by a wall of cliffs. W: 1 wonder why a slab doesn''t just break off and slide right down into the lake below. M: Oh, it will one day, but long after we are dead and gone. W: But how can you tell a glacier apart from a normal ice sheet? I mean, I''ve seen pictures of avalanches coming down the side of a mountain, and they look like they''re rolling down glaciers. M: I have no idea how to distinguish them except that a glacier seems to have a larger surface area and looks much smoother.