Tag Archives: gpr

Radars reveal Viking burial mounds and hundreds of mysteries in Norway

The ground was frozen and the field was covered with a fine layer of snow – ideal conditions for this type of archaeological research. Credit: Arne Anderson Stamnes, NTNU University Museum.

It’s not too often that archaeological research involves driving a four-wheeler across a frozen field, but in November 2019, that’s exactly what Arne Anderson Stamnes found himself doing. Stamnes is an archaeologist at NTNU University Museum, and he was using a ground-penetrating radar to survey the area.

Nowadays, archaeologists prefer to not dig randomly and carry out surveys such as this one to “see” the subsurface and learn where the interesting objectives are — and in the field Stamnes was looking, there was plenty of interesting stuff.

“Our findings included traces of 15 burial mounds, and one of them appears to contain a boat grave. Both the size and design of the burial mounds are typical of the period 650 to 950 CE—that is, what we call the Merovingian Period and Viking Age,” says Stamnes.

“A lot of the mounds are big. The largest burial mound has an inner dimension of 32 meters and must have been a towering presence in the landscape,” he adds.

Profiles (top) and a map (bottom) of the burial mounds. Note the circular features betraying the structure. Credit: NTNU University Museum

It was an excellent set of findings, partially aided by the environmental conditions. Ground-penetrating radar sends electromagnetic waves into the subsurface, from which they are reflected back to a receiver. Since archaeological objects have different electromagnetic properties than the surrounding soil, these waves are reflected differently, betraying the position of the objective. It’s a bit like an X-Ray of the underground. The four-wheeler Stamnes was driving towed such a radar that swept the area. The presence of snow also made the conditions excellent for this type of survey.

“The results are astonishingly good and they whet your appetite for more,” says Nordland county archaeologist Martinus A. Hauglid.

The burial mound that Stamnes mentions is one of the largest in the region, and must have belonged to an important chief. But archaeologists were even more intrigued by something else: an ever-so-small mysterious structure. Or rather, many of them.

Ditches, ditches everywhere

The survey revealed no fewer than 1257 pits of various sizes. Which begs the question: what exactly are they?

It’s hard to say for sure, also because they’re probably not one thing, but rather multiple things — from cooking pits to post holes to garbage pits. But what they do confirm is that this was a very active area.

“I’ve asked a few of my colleagues, but so far haven’t found anything similar to this find in other excavations. So it’s difficult to conclude what it might be,” Stamnes says.

“The shape and the fact that most of the ditches have a clear orientation with the short end towards the sea—probably also the dominant wind direction—make it likely that this was a type of house foundation,” he said.

This also seems to fit with the theory that the site was an old Viking power center. We already know that a powerful family lived in the area (based on the burial mounds), and there was a lot of activity (as evidenced by the pits), but more evidence is needed before any clear conclusions can be drawn.

“What we can say is that these pits are another sign that this area has been packed with human activity,” says Stamnes.

The site also showcased another interesting aspect: Eight of the burial mounds are circular in shape, while seven are oblong. Oblong burial mounds are associated with female burial, so there seems to be a pretty good gender balance in the area.

“Five of the round grave monuments have a diameter greater than 17.5 meters, where the largest measures about 32 meters. The long mounds are between 17.7 and 29 meters long,” Stamnes says.

“Building such large tombs is resource-intensive, so it’s plausible that the people buried here had great power and influence, both locally and regionally,” he says.

Hauglid is also thrilled, as is Ingrid Nøren, the manager for the New City—New Airport project in Bodø municipality.

“Bodøgård was the seat of the sheriff—and later the county governor—in the Nordland region from the beginning of the 17th century, while Bodin church nearby is a stone church from the Middle Ages. The burial ground that has now been discovered testifies that a political-religious power center has existed here since the Late Iron Age,” says Hauglid.

“A new city quarter has given us the chance to explore an area we’ve long been curious about. We can even see from aerial photos that there’s something under the ground. The findings from the investigation have yielded a long-awaited and exciting mystery,” concludes Nøren.

The findings are discussed in an online report (in Norwegian).

Mega canyon discovered under Greenland ice sheet

Geophysical data from Greenland have revealed the existence of a canyon comparable in size with the Grand Canyon beneath the ice sheet.

The canyon has the characteristics of a winding river channel and is over 750 km long and it is often as deep as 800 m. This immense feature is thought to predate humanity – it came to be several million years before the Antarctic ice sheet was developed.

“One might assume that the landscape of the Earth has been fully explored and mapped,” said Jonathan Bamber, professor of physical geography at the University of Bristol in the United Kingdom, and lead author of the study. “Our research shows there’s still a lot left to discover.”

Scientists used thousands of kilometers of airborne radar data collected by NASA and researchers from the United Kingdom and Germany over several decades, and managed to puzzle together the main characteristics of the Greenland canyon. They found that the geologic feature starts from almost the center of the island and ends beneath the Petermann Glacier fjord in northern Greenland.

At certain wavelengths, radar waves can travel through the ice, but bounce off the solid rock underneath. This enables us to map the depth of the canyon – the longer it takes for the wave to return, the deeper the canyon is.

“Two things helped lead to this discovery,” said Michael Studinger, IceBridge project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It was the enormous amount of data collected by IceBridge and the work of combining it with other datasets into a Greenland-wide compilation of all existing data that makes this feature appear in front of our eyes.”

Geologists believe the canyon plays an important role in transporting sub-glacial meltwater from the interior of Greenland to the edge of the ice sheet into the ocean. Existing evidence (this canyon included) suggests that before the ice sheet existed, some 4 million years ago, the canyon hosted an extensive river system which flowed from the interior to the coast.

“It is quite remarkable that a channel the size of the Grand Canyon is discovered in the 21st century below the Greenland ice sheet,” said Studinger. “It shows how little we still know about the bedrock below large continental ice sheets.”

For more information about IceBridge, the operation which led to this discovery, check out their website. The IceBridge campaign will return to Greenland in March 2014 to gather more data and develop a more conclusive picture of the subglacial features in Greenland.


When CSI and geophysics meet

We probably all know (especially thanks to the abundancy of TV series) what Crime Scene Investigators (CSI) are. Probably not so many people know exactly what geophysics is. As the name says it (geo=earth), geophysics studies the phyisical properties of the Earth, such as gravity, electromagnetism, plate tectonics, and extremely numerous other ones; it is commonly used for prospecting oil and mineral resources, as well as for environmental hazards, and even in archaeology. At a first glance, these two fields would have absolutely nothing to do with one another, but that’s not true at all.

Researcher Dr Jamie Pringle of Keele University knows how much geophysics can help CSI, by finding objects located underground or underwater, such as a murder weapon, a body, or even smaller clues. About 25% of all murder victims are dumped underwater, and 15% of them are buried, so that makes almost half of all murder victims. Some times, dogs or metal detectors are all that’s needed, but in well thought crimes, in which the killer has time to bury deeper, that’s just not good enough.

‘A lot of clandestine burials are done in a panic and those are easy to find,’ says Pringle. When dealing with more well thought out murders, it can be much more difficult, and this is where geophysics can come to the rescue.

So, in order to test the different ways of detection, a few bodies had to be buried; thankfully, it wasn’t about humans, but pig bodies, which(even though most people don’t like to admit) have a lot in common with us  – at least physically. In order to ‘see’ what’s underground, when dealing with this kind of cases, the most common method is called Ground Penetrating Radar (GPR). Initially developed to locate mines, this technology is used now also to find avalanche victims, microfissures in constructions, and small archaeological objects. The GPR got its first big break in 1994, when it was successfully used to locate the victims of serial killers Fred and Rose West.

GPR works by sending EM waves to the ground and timing how much it takes them to return. The travel time is dependant on the material through which it passes, so for example if you have a body buried somewhere, the radar will understand that the travel time for the body is different than that of the ground, and thus figure out that there is something different in there. Of course, this means that the GPR also has its limitations; first of all, it can only figure out contrasts, so if what is buried is pretty similar to the surrounding environment, the odds of finding it are minimum.

‘If you’re looking for a gun in a metal scrap yard, you’re not going to find it,’ comments Pringle.

The GPR machine is very sensitive, and the rates of success also depend on several other factors, such as soil type, how long it has been buried, and whether the body is clothed or not – a “dressed” pig is easier to find than a naked pig. Also, rough terrain is a disadvantage. This, and the fact that it is quite expensive, contribute to the GPR being relatively uncommon for the police.

‘I think the technique’s fairly well known, it’s just that it’s sometimes incorrectly applied,’ says Pringle.

Luckily, geophysicists are an inventive and smart bunch, so they use it combined with another methods, most commonly with electricity: they test the electrical resistivity, the soil’s ability to resist a passing electrical current.

‘As you decompose, your tissue and blood will mix with the soil water and give a very conductive leachate,’ explains Pringle. As a result, an electric current will flow more easily through a patch of ground where a body is buried, allowing geophysicists to spot potential graves.