In its upper course where the river channel is narrow, the river erodes downwards through the processes of hydraulic action, abrasion, attrition and solution., This downward erosion creates steep valley sides. Over time, rainwater and gravity transport soil and stones down the valley sides towards the river., As more debris from the valley sides is washed downhill, the valley eventually becomes V-shaped..

5.5 Sort it out!

由
打印
嵌入

排行榜

视觉风格

选项

切换模板

)
恢复自动保存：？