Finding What's Beneath the Ground Before It's Disturbed: Detecting Unmarked Graves and Archaeological Features
- Jul 18, 2024
- 4 min read
Not everything of significance beneath a site is marked on the surface. Historic graves may have no headstone. Urupā, wāhi tapu, archaeological remains and other cultural features may leave little or nothing visible above ground.
When development is proposed in or near a place where such features may be present, disturbing them, even unknowingly, can have serious cultural, legal and reputational consequences. Most importantly, it can cause harm that cannot be undone.
The responsible course is to understand what may be present before the ground is disturbed, so significant features can be identified, respected and protected.
Geophysics can help make that possible without excavation. This article explains how Cook Costello used Ground Penetrating Radar to map potential unmarked graves across a cemetery site ahead of proposed works.
Why these features are so easily missed, and why that matters
The difficulty is that the features most needing protection are often invisible. An unmarked grave, a filled-in feature or a site of former occupation may leave no reliable surface sign, and historic records are often incomplete.
However, the obligations around these places are real. New Zealand’s heritage and archaeological protections, and the cultural responsibilities owed to mana whenua, mean that unexpectedly encountering kōiwi, wāhi tapu or archaeological material during construction can have serious consequences. It can stop work, trigger formal notification and investigation processes, damage trust with mana whenua and the community, and create legal and reputational risk.
Finding out early is not about clearing an obstacle. It is about understanding what may be present so it can be treated with the care it deserves. It also means engagement with mana whenua, Heritage New Zealand or the relevant authorities can happen before decisions are made, rather than after an accidental discovery forces everyone to react.
How the survey works
Ground Penetrating Radar, or GPR, sends radar pulses into the ground and records the reflections that return. Changes in those reflections can indicate disturbed ground, buried features or changes in material, without the need to dig.
For this survey, a 7,000 m² site was scanned systematically at 0.5 m line spacing. A lower-frequency antenna was selected to provide suitable penetration to the depths where burials would typically be expected.
In total, 580 profile lines were collected and compiled into a three-dimensional model of the subsurface. This allowed us to review horizontal and vertical slices through the ground and identify anomalies at different depths.
What the survey found
The survey identified 27 potential unmarked graves across the site. Each showed a pattern consistent with ground disturbance within the expected burial-depth range.
The anomalies were elongated, consistent in orientation and similar in size to the marked graves visible nearby. That consistency, with unmarked features matching the pattern of known graves, gave high confidence in the interpretation without disturbing the ground at that stage.
On a site like this, that matters. The purpose of the survey was not to excavate or prove every feature by disturbance. It was to identify where sensitive features may be present, so they could be respected, avoided and managed appropriately.
What it delivers, and why it matters to councils, developers and communities
The result is a clear map of where potentially sensitive features may be present. That is exactly the kind of information needed to make responsible decisions before the ground is disturbed.
For a council or developer, it means site layout, ground disturbance and proposed works can be planned around sensitive areas rather than into them. It also means the conversations that should happen, with mana whenua, Heritage New Zealand and the community, can happen early and be informed by evidence, rather than being triggered by an accidental and distressing discovery during construction.
That protects heritage and cultural values. It also helps protect the project from the delays, redesign and reputational damage that can follow an unexpected find. Most importantly, it allows everyone involved to proceed knowing the site has been treated with care.
More broadly, this shows how GPR and related geophysical methods can help identify potential buried cultural, archaeological and historic features non-invasively before development begins.
The same approach applies wherever there is a chance of encountering something significant below the surface: former cemetery land, sites of early occupation, archaeological areas, or any development where an unexpected discovery would carry serious consequences.
Where we come in
Cook Costello carried out this survey using our in-house geophysics capability. On work of this nature, technical accuracy matters, but so does the approach. The aim is to identify and protect what may be beneath the ground, and to support proper engagement with mana whenua and the relevant authorities, not to work around them.
Because our geophysicists interpret the results themselves, we can give councils, developers and communities a clear, evidence-based picture of where sensitive features may be present. That allows those features to be respected from the outset, before layout, consent or construction decisions are locked in.
If you are planning work on or near a site where unmarked graves, urupā or archaeological features may be present, talk to us about how a geophysical survey could help you understand what may be there before any ground is disturbed.
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