Geology Reference
In-Depth Information
knick
poin
t mig
ration
A
Top of Gonghe & Tongde
basin sediments
3500
0 Ma
0.5 M
a
3300
Surveyed strath
terrace elevations
Projected tributary
mouth elevations
3100
Reconstructed pre-
knickpoint proile
Roergai
Basin
Modern Yellow
River profile
2900
Yellow River
Knickpoint Migration
Gonghe
Basin
2700
Jinguum
Basin
Tongde
Basin
2500
-100
-50
0
50
100
150
200
250
300
Distance from Tongde (km)
B
k
sn
(above knick) =
55
3800
knickpoint (from
DEM analysis)
uppermost strath
terrace elevation
3600
projected
mouth
elevation
Tributary with
Knickpoint
3400
k
sn
(correlated strath) ~
60
modern profile
Jinguum Basin
(Tertiary Sediments)
3200
30
20
10
0
Distance from Mouth (km)
10
50
C
D
Tributary
Knickpoint
Migration
Catchment
Erosion Rate
60
1
5
40
10
Be Catchment
Erosion Rate
Estimates
20
1
Distance = 1.2 Area
0.34
0
10
-1
10
0
10
1
10
2
10
3
10
4
0.06
0.08
0.10
0.12
Drainage Area at Knickpoint (km
2
)
Erosion Rate (mm/yr)
Fig. 9.19
Knickpoint migration along the Yellow River.
A. Long profile of the Yellow River, showing a pronounced knickpoint and the position of late Cenozoic basins.
The tops of the downstream basins define a gradient that projects to the top of the knickpoint 250 km upstream.
Along this gradient lie both preserved straths (black circles) and the projected former elevations of tributary mouths
(open circles). B. Example of a tributary with a knickpoint
∼
14 km from the mouth. Observed normalized channel
steepness above the knickpoint is used to project the pre-knickpoint channel gradient to the mouth (dashed line).
Multiple strath terraces (small black squares) lie along this projected profile. C. The distance of the knickpoint from
a tributary mouth scales with the drainage area upstream of the knickpoint. D. Catchment-wide erosion rates above
knickpoints scale with the normalized steepness index. Modified after Harkins
et al.
(2007).
Yellow River, they align both with the observed
straths and with the upstream projection from
the downstream Gonghe and Tongde Basins to
the top of the main-stem knickpoint (Fig. 9.19A).
Through their analysis of many dozens of
tributaries, Harkins
et al.
(2007) developed an
extensive database with which to assess both
proposed controls of knickpoint migration
and landscape responses to falling local base
level. For example, these data show a robust
relationship between upstream drainage area
and the distance each knickpoint has migrated
