Changing River Shape Flashcards

All 12 cards in this deck

Describe the long profile of a river from source to mouth.

A concave curve: a steep gradient in the upper course that becomes gentler downstream towards the mouth.

How does the cross profile of a river valley change from the upper course to the lower course?

Upper course: narrow, steep-sided, V-shaped valley. Lower course: wide, flat valley floor with a flood plain and gentle sides.

True or false? A river channel is at its deepest and fastest flowing near its source.

False. The channel becomes wider and deeper downstream, and average velocity increases because there is less friction.

Which river erosion process wears away the banks as the force of the water forces air into cracks in the rock?

Hydraulic action.

Which river erosion process wears away the bed and banks as the river's load is scraped along them?

Abrasion.

True or false? Attrition is the wearing away of the river bed and banks by the load.

False. Attrition is stones in the load colliding with each other and becoming smaller and rounder; wearing of the bed and banks is abrasion.

Which river erosion process dissolves soluble rocks such as limestone and chalk?

Solution.

What is the difference between vertical and lateral erosion in a river?

Vertical erosion deepens the channel (dominant in the upper course); lateral erosion widens it sideways (dominant in the middle and lower course).

Which two transportation processes move material along the river bed?

Traction – large, heavy pebbles rolled along the bed; saltation – smaller pebbles bounced along the bed.

Which two transportation processes carry material within the water itself?

Suspension – fine, light sediment carried within the flow; solution – minerals dissolved in the water.

Why does a river deposit its sediment?

Because its velocity and energy fall, so it can no longer transport its load; the heaviest material is dropped first.
e.g. at the mouth, on the inside of a meander, or when discharge falls after a flood.

True or false? Solution is both a process of erosion and a process of transportation in a river.

True. Solution erodes soluble rock such as limestone, and the dissolved minerals are then carried along in the water.