Davis Theory -William Morris Davis- Geomophology Chapter

1. William Morris Davis, an American geomorphologist, was
the first geomorphologist to present a general theory of
landform development. Infact, his theory is the outcome of
a set of theories and models presented by him time to time.
(1) complete cycle of river life in 1889- cyclic concept of
progressive development of erosional stream valleys
(2) Geographical cycle in 1899- sequential development of
landforms through time. According to him: “there are
sequential changes in landforms through time (passing
through youth, mature and old stages) and these
sequential changes are directed towards well defined and
end product-development of peneplain.”
Davis postulated his concept of “geographical cycle”
popularly known as cycle of erosion in 1899 to present a
genetic classification and systematic description of
landforms. His Geographical cycle has been defined as
follows:

2. • 1. It is a period of time during which an uplifted landmass
undergoes its transformation by the process of
landsculpture ending into low featureless plain or
peneplain (Davis calledpeneplane) .
• 2. Three factors-structure, process and time play important
roles in the origin and development of landforms of a
particular place. –Landscape is a function of structure
Lithology-rock types, folding, faulting joints etc), process
( agents of denudation including both weathering and
erosion-running water in the case of geographical cycle).
and time (change of landforms).
• Assumptions:
• Landforms are the evolved products of the interactions of
endogenetic (diastrpohic) forces originating from within
the earth and the external forces originationg from the
atmosphere (denudation)

3. The evolution of landform takes place in an orderly
manner in such a way that a systematic sequence of
landforms is developed through time in response to an
environmental change.
Streams erode their valleys rapidly downward until the
graded condition is acieved.
There is a short period rapid rate of upliftment in landmass.
It may be pointed out that Davis also described slower
rates of upliftment if so desired.
Erosion does not start untill the upliftment is complete. In
other words, upliftment and erosion do not go hand in
hand.
Graph:
The cycle of erosion begins with the upliftment of
landmass.

4. There is a rapid rate of short-period upliftment of landmass
of homogenous structure. This phase is not included in
the cyclic time as this phase, in fact, the preparatory
stage of the cycle of erosion. The model of geographical
cycle wherein UC (upper curve) and LC (lower curve)
denote the hill-tops or crests of water divides (absolute
relief from msl) and valley floors (lowest relief from msl)
respective. The horizontal line denotes time whereas
vertical axis depicts altitude from sea-level. AC
represents maximum absolute relief whereas BC
denotes initials average relief. Initial relief is defined as
difference between UC (summits of water divides) and
LC (valley floors) of a landmass. Relief is defined as the
difference between the highest and the lowest points of a
landmass. ADG is base level of erosion which
represents sea-level. No river can erode its valley
beyond base level (below sl).

6. Thus, base level represents the limit of maximum vertical
erosion (valley deepening) by the rivers. The upliftment of
the landmass stops after point C as the phase of
upliftment is complete. Now erosion starts and the whole
cycle passes through the following three stages.
1. Youth stage- Erosion starts after the completion of the
upliftment of the landmass. The top-surfaces or the
summits of the water divides are not affected by erosion
because the rivers are small and widely spaced. Small
rivers and short tributeries are are engaged in headward
erosion due to which they extend their length. The
process is called stream lengthening ( increase in the
lengths of the rivers). Because of steep slope and steep
channel gradient rivers actively deepen their valleys
through vertical erosion aided by pothole drilling and thus
there is gradual increase in the depth of river valleys. This
process is called valley deepening.

8. Long profile of a
typical stream.

9. C
A
B
D
E
F
G
H
Base Level
UC
LC
Old ageYouth
Maturity
AC-absolute relief
BC- Initial average relief (UC-LC)

10. • The valleys become deep and narrow characterized by
steep valley side slopes of convex plan. The youthful
stage is characterized by rapid rate of vertical erosion
and valley deepening because (i) the channel gradient is
very steep, (II) steep channel gradient increases the
velocity and kinetic energy of the river flow (III) increased
channel gradient and flow velocity increases the
transporting capacity of the rivers (iv) increases
transporting capacity of the rivers allows them to carry
big boulders of high calibre (more angular boulder) which
help in valley incision (valley deepening through vertical
erosion) through pothole drilling. The lower curve (LC,
valley floor) falls rapidly because of valley deepening but
the upper curve (UC, summits of water divides or
interstream areas) remain almost parallel to the
horizontal axis (AD) because the summits or upper parts
of the landmass are not affected by erosion.

11. • Thus, relative relief continues to increase till the end of
youthful stage when ultimate maximum relief (EF) is
attained.
• In nutshell:
• CF is parallel to AD
• UC is not affected by erosion
• LC falls rapidly
• Relief continues to increase
• Valleys are V shape and convex
• Valley form is gorge or canyon
• Long profiles of the rivers are characterized by rapids and
waterfalls which gradually diminish with march of time and
these practically disappear by the end of late youth. The
main river is graded.

12. • Graded river
• A stable stream where slope and channel characteristics
are such that the sediment discharge is enough to
provide transport for the load, but where there is no
energy for erosion. A graded river is in a state of
equilibrium. If any of the factors controlling discharge
change, the river would respond in such a way as to re-
establish grade. A river may establish grade over one
section of its course; this is a graded reach.
•

16. • Mature stage
• The early mature stage is marked by lateral erosion and
well integrated drainage network.
• The graded conditions spread over larger areas and
most of the tributaries are graded to base level of
erosion.
• Vertical erosion or valley deepening is remarkably
reduced. The summits of water divides are also eroded
and hence there marked fall in upper curve (UC) i.e.
there is marked lowering of absolute relief. Thus,
absolute relief and relative relief, both decrease.
• The lateral erosion leads to valley widening which
transforms the V shaped valleys of the youthful stage
into wide valleys with uniform valley sides.

17. C
A
B
D
E
F
G
H
Base Level
UC
LC
Old ageYouth
Maturity
AC-absolute relief
BC- Initial average relief (UC-LC)

19. • The marked reduction of in valley deepening is because
of substantial decrease in channel gradients, flow
velocity and transporting capacity of the rivers.
• Old stage
• Old stage is characterized by almost total absence of
valley incision but lateral erosion and valley widening is
still active process.
• Water divides are more rapidly eroded. Water divided
are reduced in dimension by both, downwasting and
backwasting.
• Upper curve falls more rapidly, thereby, rapid rate of
decrease in absolute height.
• Relative or available relief also decreases sharply
because of active lateral erosion but no vertical erosion.

21. • Near absence of valley deepening is due to extremely low
channel gradient and markedly reduced kinetic energy and
maximum entropy.
• The valleys become almost flat with concave valley side
slopes. The entire landscape is dominated by graded valley
sides and divided crests, broad, open and gently sloping
valleys having extensive floodplains, well developed
meanders, residual convexo-concave monadnocks and
extensive undulating plain of extremely low relief. Thus, the
entire landscape is transformed into peneplain.

22. • Evaluation of the model: Positive aspects of Davis model
• Davis model of geographical cycle is highly simple and
applicable.
• He presented his model in a very lucid, compelling and
disarming style using very simple but expressive
language.
• Davis based his model on detailed and careful field
observations.
• Davis, model came as a general theory of landform
development after Hutton’s “cyclic nature of the earth
history” (present is the key to the past’ and no vestige of
a beginning,—no prospect of an end,“)
• This model synthesized the current geological thoughts.
In other words, Davis incorporated the concept of ‘base
level’ and genetic classification of river valleys, the
concept of graded streams” of G.K. Gilbert and French
engineer’s concept of “profile of equilibrium” in his
model.

23. Graded profile is the term given to the long profile of a river in equilibrium,
when inputs and outputs are balanced. A graded profile shows a (gradient
that decreases progressively down valley;) graded to sea level.

24. • His model is capable of both predictions and historical
interpretation of landform evolution.
• Negative aspects:
• Davis’ concept of upliftment is not acceptable. He has
described rapid rate of upliftment of short duration but as
evidenced by plate tectonics upliftment is exceedingly a
slow and long continued process.
• Davis’ concept of relationship between upliftment and
erosion is erroneous. According to him no erosion can
start unless upliftment is complete. Can erosion wait for
the completion of upliftment? It is a natural process that as
the land rises, erosion begins. Davis has answered this
question. He admitted that he deliberately excluded
erosion from the phase of upliftment because of two
reasons-(1) to make the model simple (2) erosion is
insignificant during the phase of upliftment.

25. • The Davisian model requires a long period of crustal stability for the
completion of cycle of erosion but such eventless long period is
tectonically not possible as is evidenced by plate tectonics
according to which plates are always in motion and the crust is very
often affected by tectonic events. Davis has also offered explanation
to this objection. According to him if crustal stability for desired
period is not possible, the cycle of erosion is interrupted and fresh
cycle of erosion may start.
• Walther Penck objected to over emphasis of time in Davis’ model. In
fact, Davisian model envisages “time-dependent series” of landform
development whereas Penck pleaded for “time- independent series’
of landforms. According to Penck landforms do not experienced
progressive and sequential changes through time. He pleaded for
deletion of time (stage) from Davis’ function of “structure, process
and time”. According to Penck “ geomorphic forms are expressions
of the phase and rate of upliftment in relation to the rate of
degradation “.

26. • A.N. Strahler, J.T. Hack and Chorelyand several others have
rejected the Davisian concept of ‘historical evolution’ of
landforms. They have forwarded the dynamic equilibrium
theory (non-cyclic) for the explanation of landform
development.
• Though Davis has attempted to include structure, process
and time in his model but he overemphasized time. His
interpretation of geomorphic processes was entirely based on
empirical observation rather on field instrumentation and
measurement. Though Davis described the structural control
on landforms but he failed to build any model of lithological
adjustment of landforms.
• Davis attempted to explain the concept of grade in terms of
ability to work (erosion and deposition) and the work that
needs to be done.

27. • It is evident from the essays of W.M.Davis that the initial
stage of landform development (in terms of cycle of
erosion) the available energy is more than needed to
transport the eroded sediment. Thus, the river spends
additional available energy to erode its valley. As the
river valley is deepened, the sediment supply (the work
needed to be done increases) for transportation
increases but available energy decreases. Ultimately,
required energy and available energy become equal and
a condition of eqilibrium is attained. But the critics
maintain that the concept of balance between available
energy and the work to be done has not been properly
explained by Davis.

28. • It is apparent from the writings of Davis that ‘the work to
be done’ refers to transportation of debris by the rivers
and energy is spent in two ways e.g. in transportation of
debris and in valley deepening. Such division of
expenditure of energy is not justified. Thus, there are two
shortcomings-(1) erosion in itself depends on the
mobility of sediments and erosion is never effective in
the absence of sediments, (2) such condition when the
whole energy is spent in transporting the sediments and
erosion becomes totally absent is particularly not
possible.