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How does an archaeologists know where to dig?
replied to:  qwerty
Replied to:  How does an archaeologists know where to dig?
G'day Qwerty,

As an archaeologist, I think now is an appropriate time to make my first post on Absolute Astronomy... :)

There are quite a few ways archaeologists figure out where to dig.

If there are historical records or plans of the site, landscape surveys can help to figure out whereever demolished buildings once stood. The same applies for oral histories. I've just finished a dig on my "pet project"; I was digging an 1855 homestead that was demolished in 1967. Thankfully, in 1904, the local government made plans of the entire city, which are incredibly accurate. Using such plans, I figured out where the now demolished homestead was (it is now an empty field!).

Another method is to look at crop marks (and not the ones caused by UFOs!!). Crop marks indicate that there is a reduction in water below ground. This lack of water makes crops immediately above it (any type of crop, such as grass, wheat, etc) grow less healthy than those nearby. The lack of water is caused by the presence of, for instance, buried wall foundations. You can actually see where the walls of a building once were just by looking at very slight deviations in the colour of grass, etc. Walls, by their nature, cause very straight crop marks - often with other lines intersecting at right angles. There is very little chance that natural geology caused such marks! On my pet-project, I could see the marks on the ground quite easily. Check out for a much better explanation and diagrams.

One of the more high-tech solutions to finding archaeology is known as archaeological geophysics (which happens to be my specialty). This involves measuring various properties of the Earth. See . The most well-known method (although it is seldom used in archaeology) is the humble Metal Detector. The most commonly used method involves magnetometry (the measurement of the Earth's magnetic field, usually every 25 centimetres or so). Taking measurements at a regular interval, one can map out areas of higher (or lower) magnetism than the background levels. Bricks, clay pipes, and even bonfires (essentially any burnt material) has its own magnetic field, which can be detected and mapped out using this method.

Other than magnetometry, electrical resistivity is used (measurements taken in the same manner) (using a system that is slightly different from a multimeter, but I have had SOME success using an $8 AUD multimeter); this is based on the principal of soil water conducting electricity - a higher resistance indicates less water (as in the crop marks, less water = higher probability of a wall, etc. being buried there).

Ground-penetrating Radar (GPR) transmits radiowaves into the ground at varying frequencies. The frequency of the wave determines how far the waves can penetrate solid matter (this is also influenced by the density of the solid ground materials). A higher density material will reflect radar signals at a faster speed than lower density materials. Walls, typically, are more dense than soil, and so walls can be detected. Burials can also be detected due to a reduction in density (due to the cavity within the coffin).

Finally, one technique that I'd like to get more training in is landscape surveying, which involves examining the subtle changes of elevation of the soil across a site. For instance, a buried wall may raise the soil 2-3 centimetres above the surrounding soil. These are generally quite difficult to see unless from the air (because of this, aerial archaeology has played a big role in archaeological prospecting over the last century), and only under certain weather conditions.

Hope that helps. There are, of course, many more methods available...

You may wish to peruse

If there are any questions, feel free to email me at div2004 [at] - I rarely come onto this website, so don't expect a reply from me if you post here. :)