Transcript William Morris Davis

William Morris Davis
• Landform = Process + Time + Geology
• Most significant variable - Time
Youth
Mature
From Plummer and McGeary, 1996
Old Age
From Plummer and McGeary, 1996
Form Chernicoff et al., 1997
Schumm and Licthy (1963)
Figure from Ritter et al., 2002
Number of Babies
Number of Cigarettes Smoked
Systems Approach
• Emphasizes the intimate relationship
between process and form
• It stresses the multivariate nature of
geomorphology and the changes in energy
that can occur through time
– Geomorphic systems are open systems.
• Reveals that some forms may not be in
balance because they owe their character to
relict conditions.
Conceptual Models
• Process-Form: change in process
magnitudes or rates will cause a change in
form;
• Process-Response Model: Change in
process, the system will respond in order to
develop a new form.
– Process: action involved when a force induces a
change, either chemical or physical, in the
materials or forms at the Earth’s surface.
Thresholds
(after Schumm, 1973)
• Extrinsic: limits of equilibrium exceeded due to an
external factor (e.g., climatic change or tectonism).
• Intrinsic: limits are exceeded due to an internal
change in the system.
• Geomorphic Threshold: originally special kind of
intrinsic, but later suggested it could also include
extrinsic; change in landform morphology results in
a period of disequilibrium.
– Suggests that “normal” landscape development may lead to
instability and changes do not necessarily require a change
in the external environmental controls
Threshold Relationship
Northwest Colorado
From Patton and Schumm, 1975
Response Variable
Climate
Change
Response
variable
Reaction
time
Time
After Bull, 1991
Relaxation
time
Adjusted to
new condition
Decrease Increase
Climate Change
Axial Channel:
Aggradation Degradation
Hillslope plant cover
Hillslope
denudation
rate
After Bull, 1991
Time
105
Increasing Length Scale (m)
104
Profile
Gradien
t
Profile
Concavit
y
10
3
Reach
gradient
102
Meander
wavelengt
h
Bed configuration
101
Channel
width
Channel
depth
100
10-1
10-1
104
Gravel bed
streams
Profile
form
Plan
form
Crosssectional form
Bed
configuration
Sand bed
streams
100
101
Increasing Time Scale
(years)
(Modified from Knighton, 1998)
102
103
Inset fills/fans
+
0
_
Dominant
Arroyo
Process
+ Filling
0 Stable
_ Cutting
Maximum
Incision
C-Scale Arroyos
B-Scale Arroyos
+
0
_
+
0
_
Incision &
Lateral Cutting
Inset fills/fans
Point Bars
A-Scale Arroyos
1900 1910 1920 1930 1940 19501960
Scale A
1970 1980 1990
Time (years A.D.)
Scale B
Scale
C
Time
(From Balling and Wells, 1990)
From Schumm, 1973
Valley Floor Slope
Valley Instability
1
Time
A
B
Characteristics of Threshold
Crossing Events
• Lasting, non-reversible changes in process and form;
– If recurrence interval is longer than the response time, then
a threshold has not been crossed; if next disturbance
occurs before the system has recovered, then a threshold
has been crossed
• System must tend towards a new equilibrium condition
adjusted to the characteristics of the altered controlling
factors;
• Thresholds are time-dependent phenomena; the graded time
interval is most conducive to the threshold crossing concept;
• Thresholds are identified by parameters that characterized
processes and landforms.
Complex Response
Time 1
Time 2
Time 0
Incision
Deposition
Depositional
Zone
Depositional
Zones
Time 1
CrossSection
CrossSection
Re-incision
Basin Outlet
Basin Outlet
Time 2
(Adapted from Schumm, 1973, 1977)
From Yubanet.com
From Gilbert, 1917
After Graves and Eliab, 1977
From Miller, 1997
Lahontan
Reservoir
Virginia
City
11
Dayton
3
7C 7D
7B
7
6
5
9
Table
Mtn.
10
12
15
14
13Mineral
Canyon
95
Fort
Churchill
16
17
Gaging
Station
4
Pyramid
Lake
2B
Carson
City
18
2
1B
Carson
Playa
Stillwater
Wildlife
Refuge
1
Reno
395
0
Gaging
station
Fallon
Lahontan
Reservoir Carson
Lake
Lake
Tahoe
Carson
City
0 1 2 3 4 5
0
1
2
3
Miles
4
Km
Carson River
Watershed Boundary
Light colored materials are Hg contaminated mine tailings
Temperature Precipitation
Geology
Vegetation
Hydrology/Discharge
Sediment Discharge
Sediment Size
Load Type
Profile Change
Systems
•Slope Adjustment
Channel Form
Adjustment
•Scour and Fill
•Width
•Sinuosity
•Terrace Formation
•Depth
•Meander Wavelength
•Width/Depth Ratio
•Roughness
Modified from Ritter et al., 1995
•Pattern Change