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Mapping Geomorphological Environments Phần 6

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Màu thể hiện cho các đá gốc lộ ra trên bề mặt, thậm chí bị phủ bởi các đất hoặc các dạng lớp phủ khác. Mỗi một màu thể hiện cho một đơn vị địa chất hoặc một thành hệ đá riêng biệt (khi có nhiều thông tin được thu thập thì sẽ chia tách thành một đơn vị địa chất mới). | Glacial Environments lines. These are generated by the angular fragments transported by the glacier base. In particular the friction lines are usually parallel to the direction of glacier movement. Large forms of erosion The specific landforms derived by glacier activity depend on a variety of factors such as Glacier type glacier thickness the speed of glacier motion and temperature of glacier base. The bedrock structure lithology and tectonic status diaclases . The topography. Time. Large glaciers cause rock compression but little or no erosion therefore a succession of little hills and ditches can be observed. There are regions where the glacier occupies more than one basin whilst the intermediate spaces remain intact. This is the case of selective linear erosion which happens in areas of North America and Europe. Another glacier type usually restricted in the valleys provides typical forms of erosion known as the Alpine glacial relief. In this case the passage of the glacier causes the broadening and deep erosion of the valley valley geometry exhibits a U-shape . Glacial deposits The loose material that is transported and deposited by glaciers and associated streams of water is called drift. This material is the result of glacial abrasion. Drift deposits are divided in two categories Unbedded drift deposits which are directly deposited by the ice. Bedded deposits which are produced by watermelt action. Unbedded deposits Although these formations are defined as unbedded usually there are some distinguishable abrasion levels caused by the continuous advance of the glacier front. Those deposits that are composed of horizons of stratified sand can be defined as tillites and are mainly a mixture of sand silt and clay 5-50 and coarse material usually less than 10 . Some characteristics of tillites are the great variety in the sizes of rocky components the absence of sorted material the striations on the rock fragments the orientation of the elongated stones the great