Time Class
1. Review soil development including
germane processes and results;
consider chronosequences.
2. “How to” for soil descriptions horizons, texture, color, structure
3. Explain how river terraces form
4. Explain radiometric dating (14-C and
10-Be) and differential GPS
5. Channel change over human time
.
Soil Development
1
climate 1
climate 1
climate 1
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climate 1
Organisms 1
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Relief and parent material 1
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Morocco alluviated
valley, basalt
Namibia - bare
schist slopes
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Soil Chronosequence
time
1
Texture
Soil
Descriptions
2
Texture
2
Horizons
2
Color
2
Structure
2
3
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Mattole River
River Terraces formation
Strath vs depositional 3
Strath vs depositional 3
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Grant Meyer, Yellowstone
4
• Fundamental unit of matter
• Made up of components called subatomic
particles
– Proton (positive charge)
– Neutron (no electrical charge)
– Electron (negative charge)
Nucleus
Electron
4
• Carbon-14 is also referred to as:
–
–
C-14
Radiocarbon
• Types of carbon (isotopes)
Atomic mass
9
14
16
6
6
6
Atomic number
4
• The nucleus of an atom changes into a new
element
– The proton number (atomic number) must
change
– A neutron changes into a proton
– This is Beta emission or electron loss
14
14
6
7
How long does this take?
4
• The rate of decay is measured by how
long it takes for half an element to decay
(half-life)
• The half-life 5,730
of C-14
is 5,73011,460
yearsyears
years
Time = 0
1 half-life
2 half-lives
C-14
C-14
C-14
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http://lectureonline.cl.msu.edu/~mmp/applist/
decay/decay.htm
4
Cosmic Rays
(radiation)
Forms C-14
Collision with
atmosphere (N14)
C-14 combines with
oxygen to form
carbon dioxide (CO2)
4
Neutron
Proton
A neutron
is captured
N-14
7 protons
7 neutrons
C-14
A proton is
expelled
6 protons
8 neutrons
4
• Once a plant or animal dies the clock starts
• The plant or animal no longer takes in C-14
• The C-14 present in the plant or animal begins to
decay
No more
C-14 intake
C-14 continues
to decay
Radiocarbon Dating
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4
4
Spallation
n
4p
16
8
10
4
O
16
Be
10
3
n
O(n,4 p3n) Be
28
26
Si(n, p2n) Al
4
Isotope Production Rate
100%
0
0
2
4
4
35
26Al
6
30
5
25
20
4
26Al/10Be
3
15
2
10
10Be
5
0
2
4
6
8
Exposure (My)
1
10
26Al/10Be
[106 atoms g-1]
Exposure, no Erosion
Wide, shallow channel
Susquehanna
and Potomac
River Gorges
Narrow, incised gorge
Great Falls, Potomac River
Passive margin incision rates = 0.8 m/ky
Himalyan incision rates: 1-12 m/ky (Burbank, Leland)
NCALM data, 2005
Holtwood - 3 terrace levels
Where these rivers cross the fall
line (Piedmont/Coastal Plain
transition), they are incised and
bordered by terraces (mostly
straths).
Cross-Section
42 m asl to 24 m asl
All preserve flow features
Elevation (m asl)
Cross- section
Data
6 water polished
outcrops
Regular
vertical
incision
50
45
on section
incision = 0.83 m/ky
R^2 = 0.90
40
all points
incision = 0.74 m/ky
R^2 = 0.75
35
30
on section
25
off section
20
15
0
10 20 30 40 50 60 70 80 90
10-Be Model Age (ky)
Base Level Change…(Global Sea-Level)
Thousands of Years Before Present
Glaciated
Susquehanna
River
Holtwood Gorge
Mather
Gorge
Thousands of Years Before
Present
Unglaciated
Potomac
River
Mean Global
Sea-Level
(Huon Peninsula)
Global Climate Change…(GISP2 ice core records)
Thousands of Years Before Present
Susquehanna River
Potomac River
Paleostorminess
GISP2 sea salt
Degrees C
(Mayewski et al., 1997)
Paleotemperature
GISP2
(Cuffey et al., 1997)
Differential
GPS
5
Channel Change: Migrating Rivers
LS01418
Burlington, 1927
Burlington, 2004
5
Historical Aerial Photos
1937
1942
1962
1974
1980
Aerial photos of Winooski River showing change in
channel width and development of mid-channel island.
These photos were used to calculate channel change
and island development over time. Photos from Natural
Resource Conservation Service.
5
Historical Maps
1872
1906
1948
Three maps showing the field area described above. All
three maps show a mid-channel island, indicating that the
flood of 1927 completely removed the island. 1906 and
1948 maps 1:62,000.
5
River Width Over Time
Channel Width (Feet)
250
231
208
200
161
150
118
116
100
85
80
50
0
1860
1880
1900
1920
1940
Year
1960
1980
2000
5
Island Area Over Time
Island Area (Feet Squared)
35000
30000
32000
25000
21100
20500
20000
22000
15100
15000
11700
10000
5000
0
0
1860
1880
1900
1920
0
1940
Years
1960
1980
2000
Wednesday Lab
•
•
•
•
Meet in lobby
Move to the field, Richmond
Cooler weather, be prepared.
Wear sturdy shoes please, we’ll be
digging
• Old clothes, this is a dirty one
• Bakery and cremee stop? $$$