A magnetic and electrical study of archaeological structures at Loma Alta, Michoacan, Mexico

Abstract

This paper describes the results of high spatial resolution magnetic and resistivity surveys of the Loma Alta site in Michoacan, Mexico. This site is the largest of a series of man‐made earthen islands built up within an ancient freshwater basin. Occupied during three main phases from 100 BC to AD 850, the site now shows no surface detail of the underlying structural complexity. Test pits and trenches excavated during several field seasons revealed a fraction of the large ceremonial complex and provided isolated archaeological data difficult to interpret. Geophysical prospection aimed to investigate the so far unknown settlement pattern and detect architectural remains. Magnetic prospecting of the stone architecture turned out to be excellent due to the high contrast between the volcanic rock and the sedimentary fill. A fluxgate gradiometer survey of the entire mound surface defined a large number of small aligned positive and negative magnetic anomalies. Electrical surveys complemented and verified the magnetic results. A series of verification excavations exposed structural elements predicted by the prospecting and aided a further interpretation of the data. The major results of the study are discussed, as they provide a clear image of the orthogonal layout of the highly structured ceremonial site. © 1997 John Wiley & Sons, Ltd.

Advances in the Household Archaeology of Highland Mesoamerica

“…Although semiarid vegetation and certain building traditions (e.g., basal platforms and adobe or masonry walls) make houses conspicuous from the surface at many sites in the highlands, those with simpler architecture or deeper deposits remain invisible to the naked eye. Archaeologists have been successfully employing magnetometry, ground-penetrating radar, electrical resistivity, and other methods to document domestic structures and features, and to identify those that look promising for excavation (Á lvarez Díaz 2009;Barba 1994Barba , 2003Barba and Pereira 2003;Hesse et al 1997;Litvak et al 1990;Pérez Pérez 2008). Even in Teotihuacan's conspicuous apartment compounds (Fig.…”

Magnetic detection of ship ballast deposits and anchorage sites in King Herod's Roman harbour, Caesarea Maritima, Israel

“…andesites) and clay pottery fragments may also contribute to the total field anomaly (e.g. Bevan, 1994;Hesse et al, 1997) but cannot be determined from the magnetic susceptibility testing, which measures only induced magnetization. Due to the essentially random orientations of volcanic boulders and pottery materials within the ballast layer, the thermoremanent component of magnetization is likely to be very weak in comparison to the induced magnetization produced by the large contrast in magnetic susceptibility.…”

The Measurement and Analysis of Depth in Archaeological Geophysics: Tests at the Biesterfeldt Site, USA

“…Depths can be resolved in a small area with geophysical soundings; while ground‐penetrating radar (GPR) allows this, other geophysical instruments (such as resistivity, electromagnetic and seismic) can also provide depth information (Keller and Frischknecht, ; Van Nostrand and Cook, ; Parasnis, ; Nabighian, ). Archaeologicial examples include resistivity pseudosections (Hesse et al , ) and time‐domain electromagnetic soundings which measure the electrical conductivity of the soil (Slepak, ).…”