The document discusses several landforms that can result from river rejuvenation caused by a fall in sea level. Knick points form as steps where the river erodes downward to adjust to the new base level, and may create waterfalls. River terraces are abandoned floodplains left at higher levels after the river cuts down through deposits. Incised or enclosed meanders develop when the river maintains its meandering pattern while increasing vertical erosion.

1. MAKTAB DULI PENGIRAN MUDA AL-MUHTADEE BILLAH

2.  River rejuvenation occurs when there is a fall in sea level.
 Current sea level is known as a river's base level.
 This is the theoretical level down to which all rivers can be
reduced by vertical erosion.
 In reality rivers never reach this theoretical level as the
height of the land is constantly changing relative to sea
level and vice versa.
 If sea level falls then the river becomes further away from
its base level.

3.  Rejuvenation may result from causes which are dynamic,
eustatic or isostatic in nature.All of these cause the river
suddenly to erode its bed vertically (downcutting) faster as it
gains gravitational potential energy. That causes effects such
as meanders cut down as gorges, steps where the river
suddenly starts flowing faster, and fluvial terraces derived
from old floodplains.

5.  Eustatic sea level change is a GLOBAL change in sea level,
linked directly to the temperature of the Earth. In warmer
periods there is less ice and the water is warmer, so expands
and sea levels rise. In colder periods the ocean water is colder
so contracts and sea levels fall.

6.  When sea levels fall we get raised beaches, abandoned cliffs,
erosion surfaces created at the coast, and several
adjustments made to river valleys.
 These changes to river valleys are attributable to the fact
that the rivers graded profile is no longer in balance, and the
gradient of the river at its mouth is now steeper because of
the fall in sea level. In effect the water has further to fall on
its journey from source to mouth.
 This means that there is more energy at the mouth and
vertical erosion (which under normal conditions would occur
at the river's source) will occur.
 This leads to the development of knick points, waterfalls,
river terraces and incised meanders.

7. • This where the land can rise relative to the sea making it
appear that sea level has dropped.
• Isostatic changes are local changes where the height of
the land changes relative to the global sea level.
• An example of this can be found in glaciation. During
glaciations the weight of ice pushing on the Earth can
depress the crust, causing the land to fall relative to the
level of the sea. When the ice goes in warmer periods the
land rebounds upwards - rising relative to the level of the
sea.
• This process is also seen in deltas where sediment loading
depresses the Earth's surface.

10. Knick Points
 A fall in sea level, either isostatic or eustatic will result in a negative change in
the base level of rivers and streams.
 This increases the energy of the river to carry out vertical erosion and
disrupts the graded profile of the river as it attempts to erode down to the
new base level.
 Knick points appear on a rivers long profile and are, almost, like the steps
down a river takes to reach the new base level. They relate to the extent to
which a river has created a new profile in response to the new base level.
 They can be identified by a break in slope and so are often marked by a
waterfall
 They reflect the process of headward erosion as well as vertical erosion as
the river has a renewed ability to erode vertically
 Knick points often form waterfalls and, in areas where they form but there is
no alteration in rock type, they clearly show rejuvenation has occured as
waterfalls normally form due to differential erosion resulting in undercutting.

11. Long Profile Showing Knick points and
relationship with base level changes

12. River Terraces
A river terrace is a remnant or remains of a past
floodplain, which is now left at a higher level
after a river has been rejuvenated.
The process of river rejuvenation gives the
channel more gravitational potential energy
which allows more vertical erosion. This allows
the river to cut its channel down through the
former floodplain alluvial deposits (sands and
gravels) and leaves the river surrounded by the
old floodplain above.

13.  There are two types of river terraces, paired and unpaired, and they are
the remains of the former floodplain which has been abandoned because
the river has eroded too deeply for the floodplain to be accessed. London
sits on river terraces and by looking at terraces it is possible to work out
how many relative falls in base level have occurred.
 Paired:
 they are on the same level on each side of the channel and so indicate
rapid down cutting
 Unpaired:
 occur when the fall in base level is slower
 the terraces will be present on different sides of the channel at different
levels. This is because lateral erosion, through meander migration (so
mainly hydraulic action and abrasion), has had time to occur.

14. River Terraces and Paired Terraces

15. Incised/Enclosed Meanders
 They are formed when the pattern of the river is maintained as the river
increases its downcutting. The channel is deeply incised into the soft
alluvium and even into the solid rock.
 There are two types of incised meanders, ingrown and entrenched and
they can be found in areas like the Grand Canyon.
 Ingrown meanders:
 form when lateral erosion operates too (therefore indicates a more
gradual drop in base level) and so the valley floor is deepened which
means that the channel only occupies part of it.
 they have an asymmetrical cross section
 Entrenched meanders:
 created, purely, by vertical erosion (their presense indicates a rapid fall in
base level) and often form in hard rock areas.
 they are deep cut and gorge like they have a symmetrical cross section

16. For example, the Goosenecks on the San Juan River in Utah which is a tributary of
the Colorado has an incredible series of closely packed meanders in a canyon over
1000 feet high. The river makes three complete 180 deg. switchbacks and travels
more than five total miles in less than one linear mile.

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