It is the end of our third and final day at
the foot of Volcan Arenal, and we are beginning to feel that we
will miss the spectacular view of the summit as we leave tomorrow
morning for our next destination.
We spent this morning climbing down through the most dense and steep
rain forest canyon we have yet encountered in order to reach
a remote spring
site. Here, our scientific party sampled
gases emanating from springs within the stream bed. Clamoring
back up the slippery, muddy canyon wall was a real test of the groupıs
climbing skills. In the afternoon, we split into two groups, with
one returning to the vicinity of yesterdayıs spa resort, while the
other trekked up the west flank of Arenal. This proved to be a long
and arduous hike through trackless
rain forest frequently interspersed with rock slides, the
aftermath of recent pyroclastic flows. We were fascinated by the
sound of the mountain as it grumbled with bursts of gas, much like
snorts of an angry bull.
Our quest was to find a tiny fracture in a dry stream bed, where
years ago an anomalous vent of cool gas was discovered. Miraculously,
having only visited the site once, our skilled guide, Chico, found
and Alison was able to sample it. More on the special techniques
sampling follows in todayıs scientific report:
Toby uses a so-called Giggenbach sample flask after the geochemist
(Werner Giggenbach) who invented it. The gases are bubbled through
a solution of caustic soda which reacts with the CO2 and hence removes
it. The residual gases (nitrogen, oxygen, methane, and the noble
gases including helium) pass into the head-space of the evacuated
flask. Because CO2 is the major gas phase and it is removed by
the solution, the amounts of the other (residual) gases can really
build up in the head space. The more gas there is, the easier it
is to make the concentration measurement on Tobyıs gas chromatograph
in the laboratory. Dave uses evacuated gas bulbs which are constructed
of a special type of glass containing lead known to have an extremely
low diffusivity for helium. Hence, it acts as a good storage vessel
until the sample is extracted in the laboratory.
He also uses copper tubes for some samples, with the crimper tool
forming a cold-weld seal trapping the sample in the copper tube.
Because some of the gas samples, particularly those with high sulphur
contents, are corrosive to copper, we would prefer to use the glass
samplers in these cases. However, there isnıt a hard-and-fast rule
itıs determined more by the total number of samples that will
be collected on the trip versus the number of available glass samplers.
Back in the laboratory, the gases we have collected will be extracted
from their various containers and the analyses can begin. Stay tuned!