Geology 2007-2008 trip to
Arenal is an active volcano
that's been erupting continuously for the last 40 years. The
composition of the magma is richer in silicon than the runny lavas of
Hawaii, so Arenal's lavas are more viscous. On the other hand,
Arenal magmas are not as silicon rich as the really
explosive volcanoes, so Arenal's continuous eruptions have been
energetic, but not extremely dangerous. Lava erupts from the
crater both as a fluid flow and as volcanic bombs.
Arenal was shy the days we
were visiting. The upper half of the volcano was hidden by cloud
cover. On clear days, Arenal looks like this. We
were certainly not disappointed, though. It's an incredible sight!
This is the clearest view of the
peak that we saw during our stay. As you can see, it was also a
quiet period during the eruption.
Alas, this may look a little like volcanic gas and ash erupting, but
it is just cloud cover.
At the base of Arenal
volcano, an ecotourism company built a looping path through the
topography is deeply incised by creeks, so they had to build a series
of bridges. Rather than having the path dip down into each gully,
they built high suspension bridges that allow the hiker to hike through
the tree canopy.
This was our first encounter with
leaf cutter ants. They are truly amazing to watch. They
form an anastomosing current that runs in two directions. Half of
the ants walk in one direction carry pieces of leaves for their nest,
and the other half walk "empty-handed" in the opposite direction to go
and collect more. The ants were smart in their choice of paths,
generally avoiding the human path so they don't get stepped on.
Cassandra (in pink shirt) was
timid about walking the warbling suspension bridges at first. It
is a 30-70 meter drop (100-230 feet), after all! After the first
few bridges, though, she focused her mind and conquered her
fears. Abe (in hat) apparently has no fear.
This view from
one of the suspension bridges gives an idea of the height of these
things. Note the bridge by the creek for scale.
Butterfly farms are a popular
tourist attraction near many volcanoes and national parks.
We visited the one near Arenal. The butterfly tent was not as
populated as I'd imagined, but they're in the process of developing it.
The butterfly farm near
Arenal, however, has a well-stocked collection of reptiles, which I
think are the owner's true love. They house a variety of poison
dart frogs, tree frogs, and lots of
snakes. They fed one of the vipers while we were there and let us
hold their 100 kg (220 pound) python.
The tree frog must be the national
emblem of Costa Rica. They are certainly beautifully colored!
tent had a variety of beautiful flowers. This water-catching
flower (I'm a decent geologist, but my botany is weak!) was common in
This flower struck me as interesting because the pistils
are so long. It must be an adaptation for whatever pollinates the
La Fortuna Waterfall
The hike down to the La Fortuna
Waterfall descends 600 steps cut into the steep hillside. Along
the way, one can see some nice columnar joints exposed in the
cliffs. Columnar joints are a special way that lava flows
fracture during cooling. As the solidified lava cools, it
shrinks, but because it's solid rock, the rock fractures instead of
flowing. Geologists call simple fractures in rocks
"joints." These joints are shaped like giant, vertical pencils
and so are called "columnar joints."
waterfall is pretty impressive. It's worth the hike down
and the little fee to take the path back helps the local economy.
The water is definitely very, very
brisk, but tolerable to those of strong will and mind - making swimming
in the river a fun
course, since this was a geology fieldtrip, I gave a short lecture on
hydrogeology at this point, but I don't think anyone heard me. ;-)
On the drive to Alajuela (town
near Poás volcano), we stopped at a roadside shop near El Puente de Iguanas (Bridge of the
Iguanas). The trees were crawling with iguanas - some big orange ones
like this, as well as smaller brown ones. Iguanas here ranged up
to about 4 to 5 feet in length.
Bridge of the Iguanas
Sugar Cane along the roadside
As we drove around the country,
we'd see fields along the road growing things we don't see often in
Pennsylvania. Here, we stopped to sample some sugar cane.
The cane has a diameter about that of a baseball bat. Once one
strips away the outside "bark," the fibrous inside is very sweet for
chewing. Imagine chewing on some very soft wood that tastes like
sugar. We also saw teak, palm oil, banana, pineapple, coffee,
coconuts, rice, and rubber.