North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: Lake Dumond Site (3AR110), AR;
Reference: Weymouth, J.W. (1998). Final Report on Geophysical Surveys of the Lake Dumond Site (3AR110). University of Nebraska, Lincoln, Nebraska. Submitted to the Midwest Archeological Center, U.S. National Park Service, Lincoln, Nebraska.
Weymouth, J.W. (unknown). On Two Tests Using the EM38 at the Lake Dumond Site, Arkansas. University of Nebraska, Lincoln, Nebraska. Submitted to the Midwest Archeological Center, U.S. National Park Service, Lincoln, Nebraska.
The Arkansas Archeological Survey, working with the Midwest Archeological Center, National Park Service is attempting to locate a site of one of the earlier posts established near the confluence of the Arkansas and Mississippi Rivers by French explorers and entrepreneurs. Geophysical surveys, including magnetic gradiometry, electrical resistance, electromagnetic conductivity, and magnetic susceptibility, were undertaken at the Lake Dumond site, a possible location of one of these post sites. The Lake Dumond site (3AR110) ties to the east of Lake Dumond, an ox-bow lake north of the Arkansas river, and west of Menard Mound. The site is open and has been planted to pasture grass as part of the federal conservation reserve program. The grass had been cut prior to the survey so surface conditions were excellent for the survey. The site is surrounded by dense tree cover.
The geophysical survey covered thirty-four 20 m by 20 m blocks with a Geoscan FM36 fluxgate gradiometer and thirteen of those blocks with a Geoscan RM15 resistance meter. The magnetic survey resulted in a large number of anomalies, as did the resistance survey. The Midwest Archeological Center, NPS, had recently acquired a new Geonics EM38 and wished to try it out on a few blocks covered by the magnetic and resistance surveys. Because of time constraints and also because of unfamiliarity with the instrument not all modes of the EM38 were used and in fact some choices were not the best.
The conductivity measurements went well except that the dipoles should have been oriented horizontally so that the nearer-surface anomalies could have been recorded. There was little thermal drift over the time that the blocks were surveyed. Further study needs to be done to see if the EM38 can provide sufficient information so that it can replace the RM15 in most cases, since the EM38 is faster. Thermal drift is more of a problem in the in-phase mode so needs to be corrected for by frequent zero readings. Careful attention to drift can provide data that complements magnetometer data. But it does not replace magnetometer data because of the different type of measurement. Since prehistoric occupation areas can have a higher magnetic susceptibility, the EM method can provide information on occupation and middens. EM38 in-phase data should be studied in areas of known prehistoric pits such as occurs at the Hopeton site.