As glaciers move over bedrock they scrape and abrade its surface, producing fine-grained rock flour. Glaciers can also pluck away rocks up to boulder size and transport and deposit them along the margins of the glacier down in the valleys. The glaciers deposit these materials as till, a sediment consisting of mud, sand, gravel, and boulders. Much of this material is deposited in long mounds called moraines. Lateral moraines are formed on each side of a valley glacier where abraded sediment and plucked rocks are deposited.
- move over [mu:v - ˈəuvə] v. 挪开
- bedrock [ˈbedrɔk] n. 岩床
- scrape [skreip] v. 刮擦
- abrade [əˈbreid] v. 磨损
- flour [ˈflauə] n. 细软的粉末
- pluck away [plʌk - əˈwei] v. 冰川冲走(岩石)
- boulder [ˈbəuldə] n. 巨砾
- deposit [diˈpɔzit] v. 使沉积
- margin [ˈmɑ:dʒin] n. 边缘
- till [til] n. 冰渍
- gravel [ˈɡrævəl] n. 砂砾
- mound [maund] n. 堆
- moraine [mɔˈrein] n.冰碛
- lateral moraine [ˈlætərəl - mɔˈrein] n.冰川侧碛
