tailieunhanh - Mapping Geomorphological Environments Phần 4

Câu chuyện được nhiều người quan tâm về bản đồ địa chất hiện đại đầu tiên được nói đến trong tác phẩm bản đồ làm thay đổi thế giới (The Map that Changed the World) của Simon Winchester. | Fluvial Environments river or stream whose margins known as river banks are confined by the normal water flow. During a flood stage the stream overflows its banks and forms a field of flood or flood plain. MEANDER Fluvial bed form characterised by the changing direction of the bed of a stream with asymmetric banks. In contrast to other sinuous bed forms meanders show symmetry. The concave section of the stream is steep while its convex section is characterised by a small inclination. The meander form is due to the presence of some obstacle located in the eroding course of the river. This obstacle may be a hard rock more resistant to erosion than the ones surrounding it. If the meander bending is intense enough then after a time period it may cut off from the main bed and form a lobe which is a horseshoe-shaped lake. The meanders are developed mainly in the alluvial plains. If they are formed within a valley they are called embedded. The number of the meanders varies and depends on different factors such as for example the river size. The bigger the river the more the number of meanders that its bed forms. Free meanders or wandering are meanders of a small bed stream in an alluvial plain these meanders change form and migrate quickly. Meanders incised in the ground on which they flow are called incised or incosed meanders. They are not defined only by the water flow but also by the combination of the valley with its bisymmetrical alternate banks. Micromeanders are sinuous beds which are the result of the drainage micro-channels on a sloping or convex surface. OXBOW LAKE LOBE OF abandoned MEANDER A meander lobe which is cut off and abandoned by the main bed. Usually it is occupied by a lake or a marsh. PLAIN Area of relatively small height and low relief 65 Mapping Geomorphological Environments surrounded by higher areas. Its l_l SHAPE VALLEY material is of sedimentary origin VALLEY WITH PLANE and of recent age. The branches of BASE the drainage network that cross .