Core Sampling on Easter Island

Core Sampling

The only digging our team did was to take core samples at several sites in the survey area, one morning's activity. The purpose of this sampling is to quickly determine the stratification from the surface to the underlying bedrock. Interestingly enough, although the surface everywhere is strewn with rocks, the subsoil was rocky at only one location. This implies the rocks were placed on the surface and not washed down with the soil as it was deposited.

We accomplished the coring in two stages, beginning with a post hole digger and going as deep as we could. Chris takes his turn at right. He told us how he walked around the island with a tool like this recording core information for his doctoral thesis. We used the hole digger until the hole reached about two feet deep. At this depth the narrow opening made operating the tool very difficult.

At this point we switched to the extendable auger, a short handle section, several center sections, and the bit. At left, Sebastian cranks away as Carlton provides encouragement. At right Clemente extracts the extended auger and Chris checks the sample for changes in color or texture, as Sebastian, Alex, and Barry look on. The soil ranged in color from black to dark brown, turning orange as we approached bedrock. In an archaeological context bedrock means the undisturbed lowest layer. It is not necessarily actual rock, but always has the characteristic orange color of decomposing rock - rock that is becoming soil.

The picture at right shows the hollow bit with a sample. Although sometimes dry, the soil was more often moist and clayey, difficult to drill through and difficult to take from the bit.

Following teams would dig test trenches down to the bedrock at these locations, recording stratigraphy and collecting any artifacts. Based on previous experience these would be mostly obsidian chips and perhaps some burnt rock. The obsidian can be used to date layers by a technique Chris has developed. Digging through the sticky soil would be no easy task, since at one site bedrock was more than two meters down.