Case Study
Wyandotte County Cemetery
Kansas City, Kansas
The Wyandotte County Cemetery, in suburban Kansas City,
was in use from the mid 19th century up to 1973. It is thought to
contain hundreds of recorded burials, but only two graves were marked.
The locations of other burials and the limits of the cemetery were
not precisely known. A program of archaeological research was undertaken
to define the limits of the cemetery integrating non-invasive geophysical
techniques with conventional archaeological methods.
The geophysical investigation consisted of electrical
resistance and magnetic gradiometer surveys of portions of the cemetery.
Portions of the larger survey are presented here to illustrate the
response of these techniques to historic graves (the geophysical
investigation and ground truthing are discussed more broadly here).
The Geophysical investigation was followed by subsurface
testing. Limited excavation largely confirmed initial interpretations
based on survey results. Graves exposed during excavation showed
both shroud and coffin burals. This variety of burial practices
is reflected in a range of different geophysical expressions. In
general, cemetery patterning was seen as north-south rows of anomalies.
Even where individual graves were not clearly resolved, cultural
patterning was distinct from undisturbed areas, which were generally
very uniform.
Magnetic field gradient survey
Magnetic surveys are unsuited to many cemetery contexts
because igneous rock (as monuments or occurring naturally) and ferrous
metal are often ubiquitous. In this case, however, only two grave
markers were known, and if present below the surface, these materials
might be indicative of cemetery patterning. Possible targets included
buried grave markers, steel caskets, reinforced concrete vaults,
and former fences. The instrument can also detect more subtle anomalies
caused by concrete or organically enriched, disturbed, or compacted
soils, although these subtle anomalies are often obscured by the
more intense fields associated with materials such as brick, metal,
or igneous rock, and by post-depositional disturbance.
The Image below shows a high density of presumed graves
with a variety of magnetic expressions:
(mouse over image to display
interpretations)
Comments:
- Very strong anomalies (in
the colored range of the magnetic scale) are caused by materials
such as metal and igneous rock. Although these tend to obscure
more subtle patterning, they are very likely significant in themselves,
as they are largely confined within the cemetery boundaries. Possible
sources include Granite grave markers, and metal ornaments and
fixtures.
- Cemetery patterning is offset
several degrees from the survey grid, which is oriented to magnetic,
rather than true north. Although patterning may be somewhat diffuse,
the linearity and orientation of the patterning is unambiguous,
and very unlike areas outside the limits of the cemetery.
- The most obvious evidence
for burials in dataset are magnetic highs with rectilinear patterning.
The strength of these anomalies is moderate, generally 10nT or
less, and they lack a visible negative component. This is consistent
with a strongly magnetic source (such as ferrous metal, granite,
or brick) at a relatively great depth. Their patterning, oriented
with the cardinal directions, is consistent with Euro-American
burial practices. Presumed sources are vaults or metal caskets.
This type of anomaly may be interspersed with more subtle effects
from disturbed soils, or obscured by stronger effects from near-surface
phenomena (see below).
- Subtler patterning is thought
to be caused by disturbed soils. Disturbed soils may appear as
either magnetic highs or lows, or may appear less homogeneous
than undisturbed areas. In general, these effects are very weak,
and may be indistinct, but their patterning may be visible in
larger, magnetically quiet areas.
- Strong bipolar anomalies (having
positive and negative poles) are seen throughout the dataset.
This type of anomaly is caused by materials with strong magnetic
remanence (e.g., ferrous metal, granite, or brick) at or near
the surface. Sources that would be of interest would include granite
grave markers, the metal stems from plastic flowers, or corner
irons marking cemetery plots. The patterning of metal debris or
other anomaly sources not directly associated with graves may
indicate areas of general activity, and may be indirect evidence
of cemetery use. Road gravels can be seen as concentrations of
very small and weak anomalies of this type.
(A portion of this of this dataset is interpreted in more detail in Case
Study: Location of Human Burials: Magnetic Survey.)
Electrical resistance survey
Electrical resistance survey can be a very effective
method for mapping historic cemeteries. Graves may be detectable
because by the patterning of disturbed soils, or because of intrusive
materials such as concrete vaults. In general, coffins or bodies
were presumed to be too deep to be directly detectable, and the
instrument was configured to best respond to near-surface phenomena.
mouse over image to display interpretations:
Comments:
- The area showing cemetery
patterning corresponds with a flat hilltop, which is the highest
ground within the cemetery, and is thought to be the oldest part
of the cemetery. A number of large trees were present in this
area. Typically, trees tend to obscure subtle features, both because
of the roots themselves and because of differential moisture uptake.
- In spite of the trees, extensive
patterning interpreted as graves (and verified by subsurface testing)
can be seen throghout much of this area. Although individual graves
may be indistinct, the patterning of rows of graves is evident.
- A linear resistance anomaly is thought to be a former
footpath, not visible on the surface, going from the driveway
past the wooden cross.
Comparison of resistance and magnetic data
The use of multiple methods is generally complementary, and in this
case, was indispensable for a confident interpretation of cemetery
boundaries. With each of the instruments, response was better in some
areas than in others. Fortunately, areas that were ambiguous in one
dataset tended to have well-defined patterning in the other. The magnetic
map below shows the area covered by the resistance map (above).
mouse
over image to display interpretations:
Comments:
- The gravel footpath leading
from the driveway and past the crossis visible as an alignment
of weak bipolar anomalies.
- A very strong linear magnetic
anomaly may be the location of a former fence. Although bipolar
anomalies of this strength are usually caused by masses of ferrous
metal, none were found during subsurface testing in this vicinity.
Another explanation may be remanent magnetization of soils caused
by a lightning strike on a former
fence. The north-south orientation, and its alignment with an
extant gate supports the suppostion that this was the location
of a fence, and thus a likely boundary of the cemetery.
- The wooden cross appears to be newer than its
stone and concrete pedestal. It is rather roughly made, and would seem to be an improvised replacement for an earlier original. We may suppose that an original cross may have been made of iron, by association with the ornamental gate of the cemetery. The location of the cross is associated with a surprisingly
strong bipolar anomaly. It is possible that, with the posited
fence, the pedestal may have been magnetised by a lightning impact that might have destroyed the original cross.
- Although relatively weak and
indistinct, some patterning indicating graves is present. In general,
cemetery patterning in this area was much more apparent in the
resistance data.
The investigation was commissioned by the Unified Government
of Wyandotte County and Kansas City, Kansas. The Principal archaeological
investigator was Chris Schoen of the Louis
Berger Group, Inc., Marion Iowa, which contracted Archaeo-Physics,
LLC to perform the geophysical survey.
Download high reslution images
(*.PDF format)
Related content : Case
Study: Location of Human Burials
Reference:
Jones, Geoffrey
2006 The Wyandotte County Cemetery: a case study in geophysical
assessment of historic cemeteries. Proceedings of the 2006 Highway
Geophysics - NDE conference, Saint Louis, Missouri, December 4-7
2006. (view online)
