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 |
No comments:
Post a Comment