Today I took a leisurely drive between Cartagena and Santa
Marta. One of the reasons I came all this way is because I wanted to see, first
hand, the estuary of the Rio Magdalena. You might want to google a map of the
rivers of Colombia to follow this discussion. Starting with just the two main
rivers, Cueca and Magdalena, their approach to the ocean looks like a lower
case “h”. The Cueca would be the left leg, and the Magdalena the right leg. If you
follow the right leg north, it bends to the west and “captures” the Cueca
before continuing on its way north, to eventually empty into the Caribbean at
Barranquilla (Cartagena would be to the left of the “h” maybe were the dot of
the “i” would be in the pair “ih”, and it was joined to the Magdalena through a
canal dug in the 1600’s –a feat of engineering!).
Two more rivers join the Cueca and Magdalena very close to
their intersection, the Sinú and the San Jorge (are you beginning to see some
similarities between the Sacramento and San Joaquin joining just after the
Cosumnes and the Mokelumne have joined the San Joaquin?). Like in California,
the joining of four major rivers was a recipe for extensive flooding during the
rainy season. Instead of foolishly calling this flooded area a “delta”, the
clever Muiscas saw in the yearly flooding a way of banking this water.
Between 200 BC and 1000 AD, the inhabitants of the upper
estuary dug hundreds of kilometers of canals, from 1 to 4 km in length, to
“absorb” the floodwaters and store them as soil moisture for the growing of
their crops during the dry season. Between the canals, which looked like the
indentations of several fork pressing on a peanut butter cookie, the dirt being
excavated was piled on intervening ridges, which is where the farmers lived and
planted their crops. I think the following photograph is a perfect explanation
of the collection of flood water by the so-called Zinú canals:
The estuary is clearly subsiding, because one can see many
standing dead trees along the shoreline. As we all know trees don’t grow in
water, so the fact that you see a standing dead tree tells you that the area
was once above sea level.
I had lunch out there in the manglar shore: A delicious,
huge, deep-fried red snapper!
An interesting featurette of the estuary is the presence of
two or three active mud and silt volcanoes. The one I visited must have been a
good 10 m high (about 35 ft), steep, and had a crater of about 4 m in diameter.
The mud was bubbling very gently, but I was told that when the bubbling rate
increases the level of the mud in the crater rises and spills over the sides,
just like a lava flow. My hypothesis is that the organic-rich mud is undergoing
bacterial decomposition that releases CO2 (oh, no, CO2!)
in what those my students will recognize as the first stage of formation of
petroleum, and that it is the release of this gas that has given birth to these
cold mud volcanoes.
I reached Santa Marta about 2:30 pm, in perfect time for me
to find a very cute and relaxed boutique hotel, bathe my toes in the Caribbean,
and go for a long walk along the beach. My hotel overlooks the main Santa Marta
bay, a portion of which is devoted to a commercial port. Apparently there are
other adjacent bays that are a lot more quiet, but the level of night life here
is just perfect as I jot down these notes.
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