More buried soils

This morning we went back up the biggest mountain on the island to do a better job with a couple of samples we'd collected on Wednesday last week, but discovered had some problems when we looked at them carefully over the weekend. In both cases we had to make some impromptu modifications to our gear to get past problems we encountered in the local soils and sediments. In the late afternoon we had just enough time to sample a buried soil profile that was uncovered during quarrying activity recently, and pointed out to us by Charlie Love, a long-time researcher here.

Because it is in a quarry, this set of profiles is very unique -- it goes on for perhaps 50 meters and gets better and better as you walk. The most immediately striking part is that a basalt flow covered a soil, and baked the underlying soil to a bright red color. A new soil, of perhaps 30-40cm thickness has formed on top of the basalt flow. At the very bottom is another soil forming on top of a whitish rock layer (tuff).

Underneath the basalt flow, we can still see many of the features of the underlying soil. The most remarkable is the preserved structure of the root cavities of the extinct palm which once dominated the landscape here. In the photo that shows extra detail, you can see the root traces as black lines. We think the black color is a manganese mineral that forms around roots as they consume oxygen from the soil.

We sampled an area that has even more buried soils than you can see here. We hope to be able to identify the plants that grew in each soil and to find out if the plants changed over time. Finally, remember you can look at larger versions of the photos by clicking on them.

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Troy Baisden

Was Collapse Inevitable on Easter Island (Rapa Nui)? Reconstructing a Civilisation's Failure is a Marsden Programme Troy Baisden is involved in.

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