Conclusions of small- Conclusions of small- scale geomorphology scale geomorphology • Off road vehicles have lasting affects on desert environment • Channels in walkway plots are bimodal and follow the orientation of rock alignments and the piedmont’s steepest gradient • After 50 years the channels in walkway and road plots have not attained the characteristics of channels in control plots, mainly due to compaction and the rock alignments
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Conclusions of small-scale geomorphology Off road vehicles have lasting affects on desert environment Channels in walkway plots are bimodal and follow.
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Conclusions of small-scale Conclusions of small-scale geomorphologygeomorphology
• Off road vehicles have lasting affects on desert environment
• Channels in walkway plots are bimodal and follow the orientation of rock alignments and the piedmont’s steepest gradient
• After 50 years the channels in walkway and road plots have not attained the characteristics of channels in control plots, mainly due to compaction and the rock alignments
• Cosmogenic isotopes
• Tracers as sediment moves down piedmont
• Tracers at near surface to determine deposition rates
Switch from human-induced Switch from human-induced rates to long-term rates of rates to long-term rates of
landscape changelandscape change
Cosmogenic IsotopesCosmogenic Isotopes
Si
O
Ca, K, Cl
26Al, 21Ne, 3He
10Be, 14C, 3He
36Cl, 3He
The isotopes are like a suntan.
Objectives1. Sediment residence time in low
terraces
2. Depositional history of the piedmont
3. Sediment generation rates of source basins
4. Average sediment transport velocities
Three types of cosmogenic Three types of cosmogenic isotopes samplesisotopes samples
• Integrated valley samples collected from streams that exit steep narrow basins of the Iron and Granite Mountains
• Integrated soil profiles from two pits on the Iron Mountain piedmont
• Integrated transect samples collected at 1 km intervals away from the Iron and Granite Mountain rangefronts
Sampling Map Sampling Map
Valley Valley SampleSample
Transect SampleTransect Sample
Soil Pit SamplesSoil Pit Samples
Sediment generation rates
mP
C
valley data determine mountain mass erosion and sediment generation rates (Bierman and Steig, 1996):
Average sediment generation rates are 0.127 m3 y-1 m-1 for Iron Mountains and 0.098 m3 y-1 m-1 for Granite Mountains.
0
100
200
300
400
0 1 2 3 4
Nuclide abundance (105 atoms g-1)
Dep
th (
cm)
Deposition
70 m Ma-1
Stable surface
Erosion
38 m Ma-1
Predicted depth profiles for stable,erosional, and depositional surfaces
P P ex o(x / )
0
20
40
60
80
100
0 1 2 3 4 5 6
Dep
th (c
m)
15 m Ma-1
40 m Ma-1
0
20
40
60
80
100
0 1 2 3 4
15 m Ma-1
40 m Ma-1
26Al abundance (106 atoms g-1)
10Be abundance (105 atoms g-1)
Pit 1 Pit 2
N C1
sP e dzi 0
( z / )
0
h
Unconformity• Lower nuclide abundances =
less dosed sediment
• Nuclide difference represents a period of time
• Soil pit 1 10Be difference represents ~15 ka and 26Al difference represents ~6 ka