Transcript Chapter 13.2 - Stream loads and river formation

A river runs through it
Erosion & rivers
River-related vocabulary
 You may recall the following terms.
 A tributary is a small stream that empties into a
larger river.
 A watershed is the land that water runs off from
into a river.
 A divide is an elevated region that separate
watersheds.
 The path a river follows is called the channel.
 The lengthening and branching of a river is called
headward erosion.
Stream Erosion
 Rivers form when
precipitation exceeds
evapotranspiration.
 The excess water then
carries weathered soil and
rock away, and forms a
gully.
 This also causes stream
piracy, which is when one
stream “captures” another
and alters its channel.
Channel Erosion
 The edges of a stream are
called banks.
 The flow of a stream is
carrying other sediments –
these are called loads.
 The three types are
suspended, bed, and
dissolved loads.
 The movement of these
loads contributes to the
erosion of sediments in the
channel.
Discharge, gradient, and gaps
 The discharge is the
volume of water moved by
a stream in a given time.
 The gradient is the change
in elevation of a stream
from top to bottom.
 A gap is a formation of a
river through a mountain
range, usually by the
motion of isostatic
adjustments.
River stages
 A young river has a fast
headward erosion,
forming a V-shaped valley
and waterfalls.
 A mature river drains its
watershed and usually
only erodes its banks
when it floods.
 A mature river also bends
and curves, and banks
along these parts erode
faster (these are called
meanders). Abandoned
meanders are called
Oxbow lakes.
River stages
 An older river has a lower
gradient and lower
discharge.
 It usually deposits its
loads along the bank and
channel, forming a flat
plain.
 Movement of the earth’s
crust can rejuvenate a
river, and increase its
gradient and/or discharge.
Reading and assignment
 Now read pages 247-251. The following
vocabulary will appear:
 Tributaries, watershed, divides, channel,
headward erosion, stream piracy, stream load
(please also define suspended, bed, and dissolved
loads), saltation, discharge, gradient,
headwaters, water gap, wind gap, meanders,
oxbow lake, rejuvenated.
 Your homework will be to “glossarize” these
words.