Archaeological Geophysics

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Archaeological Geophysics a quick
look Magnetics, Radar, and Resistivity
Steve SheriffProfessor of GeophysicsUniversity
of Montana Missoulawww.umt.edu/geosciences
www.umt.edu/geosciences
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Bar magnetic and iron filings
Earths magnetic field
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Total Field Magnetics

• Magnetics exploits changes in subsurface magnetic
  properties
• measure subtle changes in Earths magnetic field
  at the surface
• map those changes
• Interpret the results

The best all round tool for archaeological
investigation Use for large area Use other
tools on smaller areas outlined by magnetic
anomalies
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Ground Penetrating Radar echoes off reflectors
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Ground Penetrating Radar
GPR relies on radar waves reflecting off
subsurface layers and objects Transmit receive
radar waves (200 MHz - 1000 MHZ) Make profiles
and maps of the reflectors
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Electrical Resistivity

• measures the ability of the subsurface to
  transmit electricity
• we put electrodes in the ground, connect them to
  a power source, and measure the result

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Sand Hill Cemetery served the mining towns of
Coloma and Garnet
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Electrical ResistivitySand Hill Cemetery
between the mining towns of Coloma and Garnet
Syscal Kid 24 DC resistivity switch
Electrodes cabling
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Congress would be proud we found graves under
tombstones!
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Electrical resistivity over a suspected burial
site near Coloma, MT
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Cinnabar, the historic entrance to Yellowstone
National Park
S.D. Sheriff, D.MacDonald, D.Dick, 2010,
Decorrugation, Edge Detection, and Modeling of
Total Field Magnetic Observations from a Historic
Town Site, Yellowstone National Park, USA.
Archaeological Prospection, V. 17, p.49-60.
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Magneticsyields maps and subsurface
modelsenhance and look for non-natural features
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Inverting for the subsurface shape yields best
estimates for the distribution of magnetization
causing the observations
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Total Field Magnetic, Radar, and Archaeological
Studies on the Shores of Yellowstone Lake,
Yellowstone National Park, USA
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Magnetic surveying results in maps and subsurface
models
Radar yields 3D volumes with both profiles and
time-slice maps
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TU 1 yielded a fire hearth dating to 172040
B.P. (Beta-265305), as well as abundant evidence
of obsidian stone tool manufacture
TUs 2, 3, and 4 yielded only boulders. We
excavated these, despite each individual anomaly
having the character of a boulder with remanent
magnetization, because their concentration and
alignment was promising. In a nearby area with
similar analysis one such buried boulder turned
out to be a long-term bench for flaking and other
cultural activities. At about 0.8 meters
below ground surface, TU 5 contained a fire
hearth dating to 292040 B.P. (Beta-265306).
TU 6 contained a rock concentration (likely
a hearth) dated at 3,10040 B.P. (Beta-265307).
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Total Field Magnetics Radially distributed
features around the center anomaly from an
obsidian boulder at one meter The boulder was a
long term seat for flaking The magnetic
signature of the boulder has been attenuated to
highlight the surrounding features
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Radial magnetic highs around an obsidian boulder
one meter below the surface (center anomaly) are
almost certainly cultural features the boulder
was a long term seat for flaking
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Northeastern Washington
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Magnetics Before Afterrectilinear
footprints are most likely cultural features
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Where are the boundaries of this cemetery?
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What was the layout of this 1800s mining
town? Serendipity 4 cast iron pipe!
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Missoula
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IDAHO - GPR Heres one Im excited about 75
cm deep 6-8 m diameters The old road is
shallower and not apparent on the surface
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WWII Hospital Trenches in the Philippines
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S.D. Sheriff, D.MacDonald, D.Dick, 2010,
Decorrugation, Edge Detection, and Modeling of
Total Field Magnetic Observations from a Historic
Town Site, Yellowstone National Park, USA.
Archaeological Prospection, V. 17, p.49-60.
S.D. Sheriff, D.MacDonald, 2010, Total Field
Magnetic, Radar, and Archaeological Studies on
the Shores of Yellowstone Lake, Yellowstone
National Park, USA. International Society of
Archaeological Prospection (ISAP), v. 23, April
2010, p.3-5. S.D. Sheriff, 2010, Matched Filter
Separation of Magnetic Anomalies Caused by
Scattered Surface Debris at Archaeological Sites.
Near Surface Geophysics, v. 8, 2, p. 145-150.
S.D. Sheriff and P.T. Doughty, 2009, Magnetic
and Radar Investigations of Site 45CH703,
Tumwater Canyon, Washington. Report (not
refereed) prepared for Archaeological and
historical Services, Eastern Washington
University, 46 p. S.D. Sheriff and G. Carlson,
2009, Total Field Magnetometry and Ground
Penetrating Radar Investigations at Kelly Forks
Work Center, Clearwater National Forest, Idaho.
Report (not refereed) prepared for USFS
Clearwater National Forest, 32 p. S.D. Sheriff,
2009, Archaeological Scale Magnetic and Radar
Investigations at Northwestern Yellowstone Lake,
Yellowstone national Park, USA. Report (not
refereed) presented to Yellowstone National Park
Center for Resources, Yellowstone National Park,
USA, 41 p. S.D. Sheriff, 2009, Archaeological
Scale magnetic, Electrical, and Radar
Investigations at Boundary, Washington, LPOE,
USA. Report (not refereed) prepared for
Historical Research Associates, Inc., Missoula,
MT, USA, 46 p. Schmidt, R., Crossland, N.,
Ballas, M., McKeown, and Sheriff, S., 2008,
Remote Sensing of Pineview Park Missoula Montana.
Student Project Report (not refereed) completed
for Missoula Parks Recreation Department,
Missoula, Montana.