Lets get geo-physical!

I finished up my week of work on a Roman mile-fort on the Antonine wall. As it turns out carrying out a geophysical survey is very tiring, which is why I did not post sooner. Archaeologists are supposed to be big drinkers and partiers but I was in bed by 11 this past week. At least I have a beard and cool hat so hopefully I am still in the club.

What is geophysics you may ask? Geophysics is namely used to look for valuable resources such as mineral, water and oil. The same techniques and technologies have been modified to ignore the ‘deeper stuff’ and focus on depths ranging to about 2 meters as most archaeological deposits do not go any deeper than that. Well when used for archaeological purposes a type of ‘remote sensing’ (as you can see what is beneath without having to disturb it). Geophysics is a series of methods that investigate subsurface features through their interaction with the surrounding geology.

The two types of geophysics we employed on the fort was resistivity and magnetometry. Resistivity (Rez) finds ‘anomalies’ that interferes with an electrical current that is passed through the earth. If something solid is in the path of the current, like a Roman wall, the resistance level will increase. Those who want to know more about this technique we employed the ‘twin probe’ configuration.
Magnetometry (Mag) find magnetic differences in the geology. Obviously it is very good at picking up metal but it also picks up very hot fires, such as kilns, as the high temperature may have reached the ‘Currie point’ which causes all the susceptible material to magnetically point North (unlike the surrounding area). Those who want to know more about this technique we employed a gradiometer.

Both techniques have their advantages over the other but they are actually complementary as one process along will miss a feature that the other will likely detect. Here are just a few considerations.

Rez survey requires you to physically place probes in the ground, take a reading, move forward and repeat making it much slower. Mag, however, can ‘hover’ above the ground to take measurements, which makes the process much quicker.

Mag reacts to metal so you have to strip yourself down. Apart from the obviously jewelry consideration, think of how much outdoor clothing has metal zippers, grommets or is metal toed. Rez has no such qualms,

Rez has cords which can get tangled and snagged.

Mag cannot operate near metal fences or garbage/rubbish as it will give very high readings. It also picks up modern utility pipes

All in all I have had a really interesting time and I have learned a lot. I can state that we as a team have proven that a Roman fortlet exists within a larger mile-fort along the Antonine wall. I will post the visual data later, and perhaps a link to a published report when it is finished, however I currently have to withhold the sites name for privacy’s sake.

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One Comment on “Lets get geo-physical!”

  1. Douglas Todd Says:

    ummm Blake, can you explain that geophysical thing again?

    Two words, Queen Street, and she’s been cracked wider than Blake Walkers bum at Ball’s Falls with a walnut branch sticking oot of it. Plenty o features to keep the wee kiddies happy, all Late Archaic and a few with finished Genesee and Adder Orchard points in em (can you say KEEP ALL DEBITAGE FROM ALL QUADS!). The guys with the big machines have been quite friendly and accommodating. Cara, Shaun and Nicole have been keeping the paleosol flying, Rob and Aleks are starting there too, field season 2008 has come early with heavy snow still on the ground. Bags of big Late Archaic bifaces, blackened with paleosol lay nestled in ice and snow.

    John says hi (insert call of Fowler toad here).

    Sounds like yer livin the life eh in Scotland. It must be like Fort Erie eh, one big sheet midden. Oh, they put in the Erie Beach trail. Never bothered to call, just put it thru the Erie Beach site. Nice eh? Same ol same ol…

    ciao for now
    A-Team rules!


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