Posted on by hpyszczyk

Peering Beneath The Ground: A Few Non-Invasive Archaeological Search Techniques

Archaeologists conducting a magnetic survey at Chavin de Huantar, Peru. https://www.hgiworld.com/wp-content/uploads/2011/05/Mag-Survey-Peru1.jpg

In my last post I used historic documentary records to search for lost early Euro-Canadian fur trade establishments in the remote, dense northern forests of Alberta, Canada. In this post I discuss other ways we might be able to find archaeological remains hidden beneath our feet.

Infrared Photography, Magnetometer Survey, Ground Penetrating Radar, LIDAR. Archaeologists use these non-invasive techniques to find archaeological remains hidden in remote parts of the world or where any archaeological surface evidence has been obscured by construction or other ground surface disturbance. Some methods work better than others in certain conditions. They, however, can also be misleading and potentially destructive if not used properly.

First Some Extreme Examples of Non-Invasive Search Methods

While most of the above techniques have merit, others are a little more far-fetched. In 1975 I attended my first CAA (Canadian Archaeological Association) Conference in Thunder Bay, Ontario. It was pretty cool meeting and listening to all these learned people so passionate about archaeology.

As the liquor flowed freely so were the more outlandish ideas on how to find archaeological sites without, you know, all that work (walking and stumbling around in the bush, digging endless test pits). At one of the evening receptions I noticed a bunch of people gathered around a table intently watching as two archaeologists were dangling a string with something attached to the end over the map.

I casually walked over, curious to see what they were doing. Maybe they were demonstrating some new archaeological technique that I should know about. What I saw however, surprised me. One of the archaeologist was dangling an arrowhead tied to a string over a map of southern Ontario, while the other was taking notes. I couldn’t believe what I was seeing. Dousing for archaeological sites or remains using an arrowhead on a string. Apparently the arrowhead would point to a place on the map suggesting archaeological remains were buried there.

I couldn’t resist. So I tried this method at home. The arrowhead pointed to the Royal Alberta Museum, Edmonton, Alberta. Maybe there’s something to this method after all.

Welcome to the world of some of the more outlandish methods ever used in archaeological detection, Heinz. You might have just hit an all time low. Wow! Could these learned people be serious? It seemed so. And some of those gathered around the table also seemed convinced this method might work.

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I should not have been surprised that people would use the paranormal in archaeology to help them in their investigations. Throughout the history of archaeology paranormal examples abound. Google it and you will see. Often referred to as psychic archaeology, or Psychometry, most of its claims are of a dubious nature.

In fact, it was earlier in 1974, while at my first archaeological dig at the HBC Fort Victoria, Alberta, that I was introduced to another somewhat unorthodox method of archaeological detection. Dowsing.

Dowsing (Divining, Witching) is a method whereby a person holds and forked branch or coat hangers and walks over the ground surface to detect features objects hidden beneath. Originally it was mainly used to find water (and still is) but is also applied to many other fields of detection. Including archaeology.

https://revaseybolt.com/wp-content/uploads/2019/05/Dowsing-1040×400.jpg

So we tried walking over the fort cellar depressions and palisade footer trenches holding two bent coat hangers. They were supposed to cross when you hit a buried feature. Some of the students believed it worked. Others did not. I was amongst the latter.

Even to this day, one of my colleagues (who shall remain anonymous) and I have had a 40-year debate about the merits of this technique. I’m a skeptic of any method not based in science. Others, like my colleague, are more liberal thinkers I guess. Apparently this method is supposed detect magnetic anomalies under the ground surface. That supposedly is the scientific connection. As you will read shortly not even sophisticated equipment capable of accurately measuring the earth’s magnetism are able to make that connection.

My strangest encounter (so far), while excavating at the last HBC Fort Edmonton, was with a woman who claimed, once she had held a piece of jewelry we found, it belonged to her distant relative who worked at the fort. We thanked her for her insights but did not pursue the matter any further. With this Psychometric method one holds an ancient artifact which will then send messages about its history. This method too has not gained much traction over the years among my colleagues. Nor among thieves.

Although I must admit the use of psychic archaeology is tempting when things are not going as they should in the field. My future wife and I, while at Fort Victoria in 1974, tried channeling (of sorts) one night. We tried calling up the ghost of the Clerk in charge of the fort, a Mr. Tait, I believe. We entered the old clerk’s quarters (built in 1864 and still standing on the site) at midnight. After a lot of shouting and pleading for answers we only managed to wake up a few people and totally scared ourselves in the process. I think there was liquor involved in that episode as well.

https://hermis.alberta.ca/ARHP/GetImageDetails.aspx?ObjectID=4665-0022&MediaID=129133. In 1974 when we excavated at the Fort Victoria site, the Clerk’s Quarters was in rough shape. Historic Sites Service, Government of Alberta, has done a admirable job restoring it and interpreting the site. The ghosts have probably fled by now. Either from our shouting or restoration activities.

Metal Detecting. Night hawking, as it is often referred to which, as one archaeologist put it, has had a love-hate relationship with archaeology. Yes, you can find ferric objects with this method, if that’s all you wanted to find. Even major treasures as have been recently found in England with this method. And then you rip those objects out of the ground without any proper context or worse not even recording their location. Unless palisade and building walls are made of iron, finding major archaeological features with this equipment is also problematic.

Recently, some incredible archaeological finds have been identified using metal detection. But, unless this method is used in the same controlled way as excavation, then we end up with artifacts with no context, dissociated both from other nonferrous artifacts and possible archaeological features they occur in. http://www.pastperfect.org.uk/archaeology/lo/metaldetecting.jpg
In one of here posts, archaeologist Rachel Smith has captured rather nicely what archaeology is NOT about, in this image. http://iblog.iup.edu/trowelsandtribulations/2020/04/05/dowsing-to-see/

Some Slightly More Refined Non-Invasive Search Techniques

Some non-invasive search methods have proven better than the aforementioned. But nearly all have their limitations which, if not recognized, could create more problems than solve.

When I search for historic archaeological sites, I observe the surface of the ground carefully when looking for either features on a site or the site. While some features, such as large depressions or mounds are pretty obvious, more subtle features still leave surface evidence even after hundreds of years. After clearing the vegetation off the Fort Vermilion I site, in some places the fort’s original palisade trenches were still evident on the ground surface. At Fort Edmonton, where the ground had been totally landscaped and scrubbed clean of any surface fort evidence, the north palisade was evident as a slightly depressed line where the grass grew better.

Outline of the west palisade footer trench visible in the wall and on the unit floor. These ditches are dug in the soil and then vertical poles placed in them, then filled in to form the palisade wall. Even after 200 years and numerous flooding events, this trench had slumped enough to still be visible on the ground surface.

Not only does the ground continue to slump in these trenches, the soil chemistry and water regime may also change, affecting vegetation. I have seen shell middens representing prehistoric First Nations settlements on the Northwest Coast of Canada that are totally devoid of trees (in a rain forest) because both the soil chemistry and moisture regimes have changed.

https://i.ytimg.com/vi/eCc8DP7IMVw/maxresdefault.jpg. This photograph of a buried shell midden along the Oregon coast shows the different vegetation on the top probably resulting from a change in soil chemistry and moisture.

Even normal aerial photography can produce some surprising results. For example, for years Parks Canada archaeologists could not find one of the missing Rocky Mountain House forts in central Alberta, Canada. Until one day, quite by accident, and luck, it appeared in a photograph.

Archaeologist Donald Steer, working for Parks Canada in the 1970s, was missing a fort. At least according to the historic records. One day while flying over the area someone took black and white photographs of a grain field along the North Saskatchewan River. Later when looking through them Steer noticed the outlines of what looked like a fort in the field. The outlines and cellar features of the fort were captured in the different growth rates of the wheat and shot just at the right light and angle to reveal the fort.

The use of infrared and other types of photography sensitive to different wavelengths of light are also proving useful in archaeological discovery.

During the late 1970s while excavating at the NWC Fort George (c.1792-1800) archaeologists were testing a new non-invasive technique. Ground Penetrating Radar.

The earth is surrounded by varying amounts of magnetism. Physicists found that subsurface features, such as extensive burning, or buried materials, give off different rates of magnetism often associated with human activities. If such a technique proved effective, it could help detect features at an archaeological site, saving countless hours in searching with subsurface testing.

The method has proven moderately effective but the anomalies are sometimes very difficult to interpret and can be affected by modern intrusions giving off what we call false positives – an anomaly which turns out to be nothing or created by some modern intrusion.

Nestled behind the Alberta Legislative building, stands the HBC Fort Edmonton V, c.1912. Courtesy of the Provincial Archives of Alberta.

While excavating Fort Edmonton V, we tried magnetometer survey, seismic testing, ground penetrating radar (GPR), and soil resistivity, to help find and better understand the subsurface archaeological remains. Some methods worked better than others.

Today’s Alberta legislature grounds. The lawn bowling green on the left and the skating rink (old lawn bowling green) on the right. Somewhere under there lie the remains of Fort Edmonton V.
Students, under the guidance of Dr. Edo Nyland, Department of Physics, University of Alberta, conducting a magnetometer survey on the skating rink, Alberta Legislature grounds, 1993.
This image represents a magnetometer survey done on the lawn bowling green on the left and the skating rink on the right, Department of Physics, University of Alberta. The different shaded areas represent different intensities of magnetism. According to our historic maps the remains of then Chief Factor, John’s Rowand’ Big House, should lie near the southwest corner of the lawn bowling green. Yet no magnetic anomaly is present. Either our maps are wrong, the method is too insensitive to pick up building remains (including large cellars), or, any former archaeological features were destroyed when the fort was torn down.
This is a 3D image of the lawn bowling green and skating rink, capturing nicely a recent concrete tunnel (raised area in center) running underneath the sidewalk between the lawn and rink, and the electric light posts (raised spikes) around the lawn bowling green and skating rink. And very little else. Modern disturbance is a real problem when using these techniques. And then there’s always the problem of suggesting to the lawn bowlers that we would like to dig up their lawn to check these anomalies. This didn’t go over very well. Instead we joined them for some lawn bowling.
Another method, GPR, produced some good results, showing Fort Edmonton palisade footer trench (which was first ground-proofed and evident on the surface) and the many water lines running everywhere on the site (figure on the right). We were warned by the grounds keepers not to cut the water lines because it would set off the entire sprinkling system. Of course, we accidentally cut a water line on a fine June Saturday afternoon sending numerous brides and grooms, there for their photographs, scrambling for drier grounds.

GPR has its uses but is sometimes unreliable. Not only does it create false positives (finding little or nothing of consequence) but worse, false negatives (missing things of great consequence). Imagine if you will, using this method to detect all historic graves in an area, only to miss a few before the land is developed and built on. I have seen this method miss entire cellars big enough to hide a Volkswagon in. Whether the fault of the operator, or the method, caution must be taken. However, these methods are constantly improving, becoming more reliable for archaeological work.

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Light Imagery Detection and Ranging (LIDAR). This method was developed in the 1960s by the US Space Agency and then used in the Apollo 12 missions in 1971 to map the surface of the moon. The results were spectacular.

This method uses an optical remote sensing technique that can measure the distance to a target (in this case, the ground) by illuminating the target with light using pulses from a laser. It is sensitive enough to measure ground surface elevations even under dense forests. Here are a few examples of its use at archaeological sites and features having considerable vertical depth.

LIDAR strips away all the vegetation leaving stark ground contours and relief. This is a great technique for finding mapping large features such as houses, cities and effigies such as the one you see on the right. An archaeological illusion of sorts. Sometimes when standing on the ground the objects are so big you miss or cannot identify them. Only at a distance do they become distinguishable or form a pattern.
The latest LIDAR imagery called Titan Technology has a very high resolution as this image shows. The vegetation has been stripped off Tikal, revealing the archaeological remains beneath. https://lidarmag.com/wp-content/uploads/2019/04/COVERTikal2x2km_St.png

The problem with this technique, even today, is its cost. Presently in Canada there is little LIDAR coverage of the ground surface. Fortunately for us, Alberta Forestry Service had flown parts of northern Alberta with LIDAR, including the Fort Vermilion I area.

Here was an opportunity to test just how sensitive this method was in the thick northern boreal forests of Canada. We knew where the site was located. Also some of the surface features were fairly significant. They paled in comparison to the Mesoamerican settlements, but nevertheless this was an opportunity to carry out some controlled experimentation.

Fort Vermilion I in 2014, cleared of trees and brush, revealing an uneven surface. Near the left-center of the photograph is a very large cellar depression. The largest on the site.
On the left is what our site area looks like with normal aerial photography. Only major features, such as dried up river channels manage to peak out of the dense bush. The top right circle represents the Fort Vermilion I site. On the right is the LIDAR image of the same area, now with the trees stripped off leaving all major ground surface contours exposed. One of the large cellars at the site (in the above site photograph) shows up. Just below and left are possible raised mounds (which we did not know of before). On the bottom left (circled) are two more large depressions (which we also did not know of before the LIDAR imagery results). Even in this dense bush the method worked at least on the larger surface features. It might work even better if higher resolution imagery were used. But that would be very costly.
This is a close-up of the lower left depressions on the image. We had no idea they were there or whether they were cultural. Only one way to find out.
In 2014 we found the depression and finally tested near it in 2016. We weren’t disappointed. We found animal bones, hand-wrought nails and mud chinking from cabin construction all occurring at similar depths as the archaeological remains at Fort Vermilion I (the two sites are on the same floodplain). And then we got really lucky and found this wonderful tubular glass bead along with the other materials. Currently we don’t know if this site is an extension of Fort Vermilion I, a contemporary or even earlier unknown occupation or fur trade Company, or a habitation for the local Metis freemen who might have built near Fort Vermilion I.

A Few Concluding Remarks

Inspiration for this post came when one of my readers casually asked about one of these non-invasive techniques. I replied that it was best not to get me started on that topic. Obviously, it got me started… I’ve had some good luck and some bad luck using these methods. And I firmly believe that with more experimentation and refinement they will become more reliable in the future.

We have come a long way from dangling an arrowhead over a map of Canada in hopes of finding archaeological remains. Or using coat hangers to dowse for buried archaeological remains. Some of the non-invasive search techniques are becoming more sophisticated and reliable, allowing us to detect archaeological history on a scale never imagined before.

But, occasionally I revert back to the old ways. I hoped for inspiration by sleeping in a tent on the old Fort Vermilion I site. Maybe I would receive a sign. To help me find things. And one night I received it when a pack of wolves accidentally walked onto the site sending off the most blood-curdling howling I have ever heard in my life. A message?

Beware the hazards of sleeping in remote places in Canada’s northern forests!

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