听力原文 从上一期安德森细致的观察中发现一些痕迹，我们知道了这里曾经存在过冰川，并且这些冰川对于落基山脉今天的样子起了很大的作用，那它是怎样起的作用，走进今天的落基山，听一听！

For the last few million years, perhaps three million years, glaciers have come and gone from the Rocky Mountains. And every time they come across the landscape, they are capable of eroding that landscape at rates that are perhaps fractions of an inch per year, meaning that over the course of one glacial cycle, you perhaps erode ten, twenty feet of rock.

Ice also created the broad canyons. With every ice age, new glaciers ground their way down V-shaped river valleys, and turn them into broad U-shaped canyons.

For the glacier, the whole valley is its channel, so any place where the glacier touches, the wall is capable of eroding it. And therefore the walls will be made more vertical on the edges and be flattened on the base until it gets to a now, a U-shape, which then propagates downward.

Ice also explains the presence of these boulders. They hitchhiked at the bottom of the glacier down the frozen valley, when the last Ice Age came to an end and the glaciers melted about 10,000 years ago, the boulders were left behind. Scientists had found two pieces of evidence that were responsible for the jagged looks of the Rockies today. A solitary boulder falling to the area could have only been transported here by ice. Striations （ n. 辉纹；光条纹）showed scientists that a glacier at least a thousand feet thick covered the Rockies. Ice was responsible for the dramatic shape of the Rockies today. But the mountains keep evolving. Recently, scientists discovered alarming evidence that they may collapse into a deep rift.

For the last 70 million years, compression, erosion and ice have sculpted the Rocky Mountains to their present formation, but the geology that created this impressive mountain range has also the potential to destroy it. Over the last 25 million years, a gigantic rift has been opening up at the southern end of the Rocky Mountains.

小编有约：Daisy在这一期忽然觉得在这一期冰使得这里的山谷变得很宽阔，从V形到U形，看来咱们的古话水滴石穿起到作用啦，所以有些道理还是相通的。

课后题目：在前面的几期中我们一起经历了落基山脉70多万年的经历，那么它都经历了哪些地理运动呢？听力答案

呵呵~~ 答案就在文中的"For the last 70 million years, compression, erosion and ice have sculpted the Rocky Mountains to their present formation, but the geology that created this impressive mountain range has also the potential to destroy it. "你知道在哪里吗？

参考译文

在过去的几百万年，也许是300万年前，落基山脉的冰川已经开始在融化了。只要这些融化了的雪水到过的地方，每年就会侵蚀大约一英寸地，这就意味着，在一个漫长的冰期旋回过程中，可以侵蚀掉岩石十到二十英尺深。

这些冰还使得峡谷更加宽阔。每一个冰河时代，新的冰川向下流动，经过V形的河谷，慢慢地使这里变成了宽阔的U形峡谷。

对于冰川来说，这里的整个山谷是它的渠道，所以只要冰川流过的地方，都能被侵蚀掉。冰川到过的地方，墙壁边缘会变得更加垂直，过不了多久，慢慢地就变成了平地，一路向下直到把峡谷变成现在的U形。

这些冰同样也可以解释巨石的存在。当最后一个冰河世纪结束的时候，巨石搭乘冰川的顺风车来到了结冰的峡谷，冰川早在一万年前融化，巨石则留在了这里。科学家们发现了两件证据，使得今天的落基山脉看起来就像锯齿的样子。孤伶伶的巨石仿佛告诉人们只有冰才能够有这个力量把它们带到这里。科学家还通过这里的条纹推断出这儿的冰川曾有几千英尺厚。可以说现在落基山脉的巨大变化归功于冰所赐。山仍在不停的变化。最近，科学家发现了一项令人震惊的线索，落基山脉随时可能会崩溃并陷入深深的裂痕当中。

在过去的70万年内，经历过压缩，侵蚀和冰川的塑造使得形成了落基山脉现在的样子，但是地理的变化却始终没有停止，它也完全有能力摧毁这些山脉。在过去了的25万年，落基山脉的南端已经形成了一个巨大的裂痕。

重点讲解

注释：① channel vt. 引导，开导；形成河道 n. 通道；频道；海峡
[ 过去式channeled或-nelled 过去分词channeled或-nelled 现在分词channeling或-nelling ]
词组：
marketing channel 销售渠道，行销通道
main channel 主通道
change the channel [美国俚语]转移话题
english channel （英法之间）英吉利海峡
distribution channel 分销渠道；销售渠道
communication channel 通信信道；通信电路
river channel 河道；河槽；船舶航道
例句：
1. Mr Obama's speech was broadcast live by only one cable TV channel with limited reach.
奥巴马的演讲只通过一家有线电视频道在有限的范围内现场直播。
2. But after his landslide 10 years earlier he could have crossed the English Channel on foot.
但在10年前以压倒多数胜选上台后，他本可以信步跨越英吉利海峡。

② presence n. 存在；出席；参加；风度；仪态
词组：
in the presence of 在…面前；有某人在场
in presence of 提示
physical presence 实体存在；实际存在
military presence 军事存在
internet presence 网上广告
commercial presence 商业存在
例句：
1. I mean by that , your presence will become meaningless .
我的意思是，你的存在会变得没有意义。
2. For these the presence of people is central to the experiment.
由此说来，人类的存在正是这项实验的核心。

③ impressive adj. 感人的；令人钦佩的；给人以深刻印象的
[ 比较级more impressive 最高级most impressive ]
例句：
1. At first glance, all this has produced some impressive results.
初看之下，这些措施都产生了明显的效果。
2. This is the most impressive architecture I've seen on this trip.
这是我此次旅行见到的最令人难忘的建筑。

句子讲解：

1. And every time they come across the landscape, they are capable of eroding that landscape at rates that are perhaps fractions of an inch per year, meaning that over the course of one glacial cycle, you perhaps erode ten, twenty feet of rock.

　　【结构简析】整个句子是冰川每年侵蚀大约一英寸土地来做解释说明的。主句为"they are capable of eroding that landscape at rates"。

【参考译文】只要这些融化了的雪水到过的地方，每年就会侵蚀大约一英寸地，这就意味着，在一个漫长的冰期旋回过程中，可以侵蚀掉岩石十到二十英尺深。

　　2. They hitchhiked at the bottom of the glacier down the frozen valley, when the last Ice Age came to an end and the glaciers melted about 10,000 years ago, the boulders were left behind.

【结构简析】 我觉得这个"hitchhike"这个词用的非常好，这些石头就像搭便车的人一样，这个比喻迅速就让人明白是怎么一回事啦。很形象。

　　【参考译文】当最后一个冰河世纪结束的时候，巨石搭乘冰川的顺风车来到了结冰的峡谷，冰川早在一万年前融化，巨石则留在了这里。