Saturday, August 3, 2013

Kotzebue to Kodiak: A GPR Survey Tour

While Molly has been in Angoon, I have been doing a bit of fieldwork myself.  First it was back to Kotzebue for another round of ground penetrating radar surveys.  The field work went quite well and it was nice to be going back to the same place to work.  On the first trip to Kotzebue there was a lot of uncertainly in how well the GPR would work and what the site conditions would be like.

With the GPR in state I saw an opportunity to demonstrate its capability at the Alutiiq Museum's community archaeology dig in Kodiak which was just moving into its second week.  I have often volunteered at this dig and Molly has worked there several time.

The effectiveness of GPR can vary widely depending on a number of factors including soil properties, vegetation cover, and the features you are seeking to detect.  This seemed like a great opportunity to test the GPR in Kodiak and demonstrate its effectiveness and limitations to the Alutiiq Museum's archaeologist and the volunteers working at the site.  The rental company Northwest Geophysical donated the equipment use for three additional days.

With the help of my friend John we were able to survey two areas with the GPR, one of which was directly adjacent to the active dig site.  By comparing the GPR data to the adjacent excavation and to multiple soil probes we were able to interpret the features seen in the data.  The GPR seem to be effective at mapping late prehistoric house pits that have been filled with Katmai volcanic ash, but is unable to detect horizons below the ash and above the glacial till.  It also appears that the GPR can detect fire hearths although I did not see one in the second house pit we surveyed so perhaps it was small or we just didn't detect that one.  Hopefully the museum will excavate one of features we surveyed next year allowing us to better ground truth the GPR data.

John packing in much of the GPR to the survey area

Partially excavated house pit can be seen in the side wall of the archaeological excavation

GPR ready to survey adjacent to the excavation
GPR data overlaid on an oblique photograph

GPR radiogram with my interpretation of the stratigraphic horizons.

1 comment:

  1. Ryan, Never fear we'll be testing your housepit next year. I was very impressed with what the GPR did see, and I will be posting my thoughts on your finds soon! Patrick