Sunday, 18 October 2015

If I had a hammer…

I’d hammer in the morning, I’d hammer in the evening…

Two weeks have passed since we started taking cores from our platform on Lake Hamana and loads of mud and sand has been lifted out of the lake floor. Our Belgian coring team is starting to work like a well-oiled machine. Hence, about time to introduce you to our floating home and how we manage to sample more than 8 m of bottom stratigraphy.

Our platform is held in position by four anchors and consists of four rubber floaters, a 3x4 m standing surface with a central opening and a tripod to which three winches are fastened. Each of these winches holds part of the coring equipment, which is guided through pulleys at the crest of the tripod. One winching cable is attached to the hammer weight, one to the piston and one to the entire system (coring barrel, hammer weight and piston).

Leaving the marina
Parts and components of our floating home
Arriving at destination... Time for anchoring!

The length of each core section depends on the length of the used coring barrel, in our case 2 m. For retrieving a 2 m core section, let’s say from 0-2 m below the lake bottom surface, the coring system in its total is lowered to just above the sediment-water interface with the piston at the bottom of the barrel, in which an empty plastic tube (liner) is placed. The piston is then fixed in one place by a cable while the hammer weight is manually moved up and down repeatedly in order to push the barrel with liner into the sediment. Because the core barrel is moving, but the piston isn’t, a vacuum develops between piston and sediment, allowing the sediment to rise easily into the barrel despite the friction. When coring for a deeper section, e.g. 6-8 m, the entire coring system has to be extended with lengthening rods and hammered up to a depth of 6 m below the lake bottom surface before fixing the piston… which can be an exhausting task, especially when lots of sandy layers have to be pierced. After all the hammering, the system with sediment sample can be pulled up again. The now full liner has to be closed off carefully with caps and tape at both ends. Aaaaaand… time for the next section!  

Cartoon of the piston coring procedure

Two hammerers, twice as strong!

Exhausted hammering crew

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