Today, we began coring Rano Raraku, the crater lake around which almost all the moai were carved. Rano Raraku has been cored more than any other lake on the island, partly due to interest in the statues and partly because it yields beautiful sediment cores. Most of all, access is easy.
For us, Rano Raraku meant a contrast from working in the open on a floating vegetation mat. We were cooped up on a very small raft for the entire day. Today's photo shows a silhouette of David efficiently operating the corer. In the background, you can see the open 9-10m core and 9m of core neatly stacked in boxes.
We'll be continuing to collect sediment cores from Rano Kau for the rest of the week. So far, it looks like we're achieving promising results. Today's picture shows a nice 50 cm sample from one of our two devices. It shows some good layered sediments, as well as some fibrous vegetation that was dragged along on the outside of the corer.As you can see from David's shirt, this is a grimy job. When done well, it produces excellent results.
Today we began our efforts to core Rano Kau, the massive crater lake at the southwest end of Easter Island. Getting there is a challenge in itself. The walk down to where we are coring is a descent of 300m across boulder slopes and then out onto the floating mat that covers the lake.
Our first hole reached 20 meters below water level. Like most previous work in Rano Kau, we found entirely organic sediments (today's second photo shows an ideal sample from deep in the core). These organic layers are derived entirely from vegetation. We were pleased to find the organic layers interrupted by at least two layers of clay, silt and fine sand that may indicate ancient landslides from the crater rim.
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.