SPATIAL ANALYSIS OF CHARCOAL HEARTH DISTRIBUTION AROUND A PENNSYLVANIA IRON FURNACE

Charcoal iron production was a major industry in Pennsylvania from the early 1700s to the mid-1800s. The charcoal from approximately one acre of woodland was needed to fuel the average iron furnace for one day, so the availability of forested land and the supply of charcoal were factors that frequently limited the life of a furnace. Many individual charcoal hearths, which were flat, cleared areas where cut wood was stacked and prepared for charcoal production, are known to be present on the mountain slopes around remaining furnace ruins, but relatively few have been specifically identified. The community of Greenwood Furnace in northeastern Huntingdon County, Pennsylvania, was a busy industrial complex based around charcoal iron production, and required the production of large amounts of charcoal from the surrounding forests. In our study, many charcoal hearths were readily viewed in shaded relief images of the LiDAR digital elevation model (DEM) as circular features resembling small craters. The LiDAR data was primarily acquired to produce an accurate and high-resolution bare earth model of Pennsylvania (3.2-foot pixel, 1-meter equivalent raster GeoTIFF DEM). Approximately 500 historic charcoal hearths were readily identified in a 10359 hectare (40 square mile) area surrounding Greenwood Furnace and were manually identified as shaded relief images. Strings of hearths were readily evident along similar topographic contour lines on the adjacent hillsides. Adjusting the sun angle for azimuth and altitude was very effective in confirming hearth sites. In this study, we employed various methods of spatial analysis such as pattern and cluster analysis, to evaluate the observed distribution of relic charcoal hearth sites. These results are related to the regional topography and the economics of charcoal transportation as they influenced the life of the iron furnace.