2 August 2009 Sunday The Drilling Process

Sediment cores are harvested in 2.5 inch diameter polycarbonate tubes that are tamped into the lakebed with a weight.  The tubes are fastened onto a coring head and collar with large hose camps to hold them firmly in line with the weight by a threaded rod that passes through both of them. 

Both the coring head and the weight are attached to ropes which are used to lower them together to the lake floor, then the rope for the weight is pulled up a little and dropped repeatedly as the line on the tube is played out carefully for an additional amount about as long as the tube.  For short cores this is about one meter. 

Both ropes are pulled up simultaneously until the open mouth of the core tube is just below the surface.  One of the team then reaches into the water and pushes a cap on the tube so the sediments (which have to this point been held in place by suction) do not have a chance to slide out and destroy the integrity of the core.  That important suction has been created during drilling by water in the tube being forced out through a one-way valve on the collar as the sediments push up into the tube. Once the core is in the boat, the valve on the collar is opened to release the suction, the clamps are loosened, and the tube is separated from the corer.  Another cap is put on the top and the core is stored carefully, upright, until it can be further treated back in camp.  The cores we have collected from Cascade Lake and High Lake have been about one meter long and are referred to as "short cores." In the next few days we will be going to another lake where we will be using a more sophisticated coring set-up to get cores up to 8 meters long. I will try to have good photos of that to show you. At Cascade Lake we were coring from the Zodiac and we would return to camp to work with the cores. After we broke camp there we had our pilot make a brief stop on High Lake where Darrell and Heidi managed to get 2 cores working from the pontoon of the float plane. It was a little tricky, balancing everything and not having much room to move around, but they got the job done!