It happened once more, as predicted by Pythagoras and Galileo’s Music of the Spheres. Our Moon passed in front of our Sun, just far enough this time that it didn’t quite hide it all the way to its borders. The Sun’s Corona was not revealed but created what has been called a ring of fire.
I have had the pleasure to watch several solar eclipses in my life, including total ones and believe me: nothing matches a total solar eclipse! Next best to me are annular eclipses like the one we just saw across the American continent. I got to see one as a child and I remember very well watching it with a solar filter on my telescope.
Costa Rica, where I live, was not quite in the best place to see the ring. We just got a more darkened than usual partial eclipse. What to do? I decided to photograph the light spots formed by tree leaves that are actually a pinhole-camera like projection of the Sun. Instead of being round they look like crescent moons during a partial solar eclipse.
Yes, I also got a photo of the Sun when clouds were moving in and I was able to make a photo without filters.
Have you seen the little crescents on the ground before?
The Rio Celeste is formed at the junction of two mountain rivers with crystalline waters that originate on the slopes of Tenorio Volcano, in Northern Costa Rica. One is clean water Buenavista River. The other is Quebrada Agria (Sour Creek) which owes its name to the fact that it contains dissolved sulfuric acid, aluminum and silica. When the two streams come together at the site known locally as the “Teñidero,” (Dyeing Shop) the mixture produces a suspension of particles with sizes less than a thousandth of a millimeter that scatters the blue component of sunlight and gives Río Celeste its beautiful turquoise color.
Although very clean water sometimes appears blue in the ocean, rivers and lakes, this is because water can slightly absorb light in the red part of the spectrum and lets the blue part through. However, this effect is very weak and is only noticeable when the water is several meters deep. The most common, however, is that due to the presence of algae or suspended mineral particles, the water of many rivers looks greenish, reddish or brown.
When water looks turquoise in waters of glacial origin or in volcanic regions such as Rio Celeste, we also notice that it is not completely transparent due to suspended material and its color is due to Mie Scattering. It receives this name in honor of the German physicist Gustav Mie who was the first to describe the mathematics of the phenomenon. The exact color of the scattered light depends on the size of the particles and the light source, but it is usually a blue-green or cyan color, close to what we know as “celeste” in Spanish. The blue (actually cyan) color of the sky is also due to the scattering of light, in this case by molecules in the atmosphere and is called Rayleigh scattering which is a special case of Mie scattering when the particles are much smaller than the wavelength of light.
In glacial waters and in the Rio Celeste, visible light falls on particles with a size comparable to its wavelength, which is 0.4 to 0.7 micrometers (thousandths of a millimeter). In these cases, the reddish component of the spectrum, of longer wavelengths, continues on its way but the bluish component deviates in all directions, that is, it is scattered. As the rays are scattered in all directions, part of the light we see directly from the above the water surface but another part is in turn reflected by other particles towards us. In the meltwater of glaciers this is produced by finely ground rock particles called “Glacial Flour.” In Costa Rica we do not have glaciers but the lake of Poas Volcano’s active crater shows a similar light-blue color due to Mie scattering of light in this case by colloidal sulfur particles. Let us note that in the scattering of light the color does not correspond to that of the material of the particles because they are not large enough to be directly observed. For example, during our investigations we have found that Río Celeste particles are in fact a complex mixture of colorless silicon and aluminum minerals.
To further understand the color phenomenon of Rio Celeste we would have to delve into Mie’s Theory of electromagnetic wave scattering. We will define scattering as the change in direction that waves experience when they encounter in their path obstacles of a size comparable to their wavelength. An everyday example of scattering are sound waves that change their direction at doors and that is why we can hear sounds from other rooms even if we do not have a direct line of sight to the source. The mathematics of the Theory are complicated but the theory successfully explains all scattering processes from the color of the sky to the operation of Radar. In the references there is an article illustrating the change in color of scattered light as a function of particle size and the more physically and mathematically inclined can then read it and learn more about it on the internet.
Image. In the “Blue Pond” you can see that water of Rio Celeste is a little greener than the color of the sky. The exact observed color depends on environmental factors such as the color of the river bottom and the power spectrum of the illuminant, in this case the direct Sun.
Initially we managed to explain the color of Rio Celeste based on a mathematical model of Mie scattering developed by Dr. William Vargas from the School of Physics and CICIMA, University of Costa Rica, based on careful measurements of the size distribution and properties of the particles that form in the Teñidero made by Drs. Erick Castellón (School of Chemistry and CICIMA, UCR and Dr. Max Chavarría (also from the School of Chemistry, CIPRONA, UCR, and CENIBIOT) together with researchers from Costa Rica National University.
Our subsequent work has extended these initial results, giving us a clearer idea of how the particles are formed in the Teñidero. We now know that what occurs is a chemical reaction between the soluble species of sulfuric acid, silicic acid and aluminum from Quebrada Agria with the alkaline ions from Buenavista River. The reaction rapidly generates the colloidal aluminosilicate particles that scatter blue light in Río Celeste.
But, where do the acidity and ions of Quebrada Agria come from? The answer comes from other work we have done on the Río Roble, the tributary that joins the Rio Celeste at Laguna Azul (Blue Pond). Dr. Max Chavarría and his collaborators found that in the hydrothermal water and gas vents we see at Los Borbollones, underground hydrogen sulfide is oxidized to sulfuric acid by microorganisms:
H2S + 2 O2 → H2SO4 + energy
These are sulfur-oxidizing bacteria of the genera Sulfuriferula, Halothiobacillus and Sulfurimonas that take advantage of the chemical oxidation of sulfur with oxygen to obtain metabolic energy. The sulfuric acid produced by this reaction attacks the rocks, mainly dissolving the feldspars, with which the aluminum and silicon pass into the aqueous phase as Al3+ ions and silicic acid (H4SiO4).
The Quebrada Agria (Sour Creek) originates as a common mountain river but comes into contact with hydrothermal vents such as those of Roble River which turn it into an acid current with a pH of 3-4 (an acidity between that of lemon juice and that of orange juice) due to the reaction with the rocks of the riverbed. The Buenavista River, with a pH of 7-7.5, like clean mountain rivers, contains basic bicarbonate ions (HCO3–) that can neutralize the acidity of sulfuric acid. In addition, the Buenavista River contains silicic acid, a product of the dissolution of siliceous shells of its abundant diatoms and also of the soils rich in volcanic glass on the slopes of Tenorio Volcano. The two currents resulting mixture acquires an intermediate pH of 5-6. At these pH values solid aluminum hydroxides begin to form but in the presence of silicic acid they quickly become a colloid of hydroxyaluminosilicate particles that scatter blue light.
The chemistry of Rio Celeste :
First, bicarbonate ions from the Buenavista River neutralize sulfuric acid from the Quebrada Agria:
2 HCO3– + H2SO4 → SO42- + 2 H2O + 2 CO2
But the Buenavista River is fast enough to leave behind unreacted bicarbonate, which produces hydroxide ions.
HCO3– + H2O → H2CO3 + OH–
Hydroxide ions react with aluminum ions from Quebrada Agria forming Al(OH)3
2 Al3+ + 6 OH– → 2 Al(OH)3
Finally, the silicic acid reacts with the aluminum hydroxide generating hydroxyaluminosilicates of approximate composition (Al2O3)(SiO2)2•3H2O as amorphous particles due to their rapid formation rate.
Note that if there were no silicic acid in Quebrada Agria then hydroxyaluminosilicates would not form. This is an important difference with respect to acidic rivers in other regions.
Hydroxyaluminosilicates belong to a group of minerals that do not form crystals and are known as Short-Range Ordered Aluminosilicates (SROAS). Their chemical bonds are similar to those of Imogolite and Allophane SROAS and they are found in volcanic soils called Andosols that are common in Costa Rica. Imogolite and Allophane have definite shapes of tubes and hollow spheres respectively. The hydroxyaluminosilcates for their part do not have such a defined structure.
Our group from the University of Costa Rica took water samples from the Río Celeste and isolated the particles by filtration through a very fine membrane. Next, we characterized the particles using Electron Microscopy, Powder X-ray Diffraction and Infrared Spectroscopy techniques at the School of Chemistry and at the Center for Materials Science and Engineering Research (CICIMA). By means of a comparison with the properties of synthetic SROAS just recently reported in the literature, we were able to verify that indeed the particles of the Río Celeste are recently formed hydroxyaluminosilicates. In the references you can consult the work that we did together with international collaborators in Germany and Sweden for the study of the microbial communities involved.
Hydroxyaluminosilicates are of great environmental importance as they keep aluminum ions, toxic to life, trapped within a highly insoluble solid, separating them from drinking water. The environmental chemistry of silicon and aluminum are thus closely linked and affect all biological systems.
We owe our success in the study and exploration of the Río Celeste system to the support of the National System of Conservation Areas (SINAC) and especially to the energy and enthusiasm of Master Isaac López Núñez who currently manages Tenorio Volcano National Park. We are deeply grateful to him and the Park staff for their support.
We conclude by mentioning that in Costa Rica we also find rivers with blue waters on the slopes of Poás and Rincón de La Vieja volcanoes and we are also investigating them. These other blue rivers in Costa Rica are just as beautiful but they take on their color slowly, over several kilometers. As far as we know, they do not seem to have a Teñidero like the one on Río Celeste. Observing two colorless streams that join in the middle of the tropical forest and instantly turn into a river with waters dyed the color of Heaven is a natural miracle that Costa Ricans must witness and admire.
Further Reading
Arce-Rodríguez, A.; Libby, E.; Castellón, E.; Avendaño, R.; Cambronero, J. C.; Vargas, M.; Pieper, D. H.; Bertilsson, S.; Chavarría, M.; Puente-Sánchez, F. Out of the Blue: The Independent Activity of Sulfur-Oxidizers and Diatoms Mediate the Sudden Color Shift of a Tropical River. Environmental Microbiome2023, 18 (1), 6. https://doi.org/10.1186/s40793-023-00464-2. – Our recent work on the characterization of Río Celeste particles and their formation mechanism. The main source for this post.
Beardmore, J.; Lopez, X.; Mujika, J. I.; Exley, C. What Is the Mechanism of Formation of Hydroxyaluminosilicates? Scientific Reports2016, 6 (1), 30913. https://doi.org/10.1038/srep30913. – A description of the initial stages of formation of hydroxyaluminosilicates.
Exley, C.; Guerriero, G.; Lopez, X. Silicic Acid: The Omniscient Molecule. Science of The Total Environment2019, 665, 432–437. https://doi.org/10.1016/j.scitotenv.2019.02.197. – Silicon and aluminum in biological systems. References to the authors previous work on this topic.
Levard, C.; Doelsch, E.; Basile-Doelsch, I.; Abidin, Z.; Miche, H.; Masion, A.; Rose, J.; Borschneck, D.; Bottero, J.-Y. Structure and Distribution of Allophanes, Imogolite and Proto-Imogolite in Volcanic Soils. Geoderma2012, 183–184, 100–108. https://doi.org/10.1016/j.geoderma.2012.03.015. – SROAS formation and discussion of tetrahedral and octahedral aluminum sites in their structure.
Arce-Rodríguez, A.; Puente-Sánchez, F.; Avendaño, R.; Martínez-Cruz, M.; de Moor, J. M.; Pieper, D. H.; Chavarría, M. Thermoplasmatales and Sulfur-Oxidizing Bacteria Dominate the Microbial Community at the Surface Water of a CO2-Rich Hydrothermal Spring Located in Tenorio Volcano National Park, Costa Rica. Extremophiles2019, 23 (2), 177–187. https://doi.org/10.1007/s00792-018-01072-6. – Source of water’s acidity in Los Borbollones.
Some landscape photography books and websites claim that sunset photos are amateurish and should be avoided by true Landscape Photographers as they are plain boring.
Really?
One of the most inspiring views in our planet is an spectacular sunset, or a sunrise if we are early risers. It is no surprise that we all aim up our cameras to remember and to share the view. I’ve seen simulations of Martian sunsets and they look sad and nearly colorless. I will not be a colonist there, trust me. In the Moon, with no atmosphere, they are just black!
So here I am, sharing yesterday’s sunset in my corner of our beautiful planet. I hope you will find it as pretty as it looked to me!
An ultrawide lens (anything below 24 mm in 35 mm equivalent format) can provide a sweeping view of an open landscape, but I also find it important for crowded forest and tree covered environments.
The widest rectilinear lens I own is an 11 mm lens by Irix and it is an excellent lens, but these pictures are made with other lenses. They are landscapes I made while testing an ultra wide 11 mm lens by Venus Optics on my Z7 alongside a 12 mm Samyang fisheye lens. I no longer own either lens but the photos I made that afternoon are good representatives of what can be done with these optics.
One thing I sometimes dislike about ultra wide rectilinear lenses is that elements in the corners of the image can look too stretched, like sucked into the frame. Because of this, I sometimes actually prefer using a fisheye lens: when used carefully, one can can hide the strong deformation we associate with their extreme projection. By keeping the horizon near the center of the frame, it remains straight on a fisheye lens image. In other cases, the image can be reprojected (defished as some people call it) to avoid the curved corners.
You can be the judge now and decide if this approach works as I really wanted to include nearby elements from a restricted point of view: I was literally shooting from a barbed-wire fence in all the photos I show here.
Have you tried using fisheye lenses for landscape photos?
One of the prettiest beaches on Costa Rica’s west coast is on the inside of a circular bay that gives protection to the swimmers from the open ocean waves and is named Carrillo Beach.
A mountainous, tropical country like Costa Rica is bound to have plenty of waterfalls. This is the second part of my previous post: mountain river, waterfalls and lush tropical vegetation with great weather.
Thanks to a partial lifting of our restrictions, and a couple days of good weather, we got the chance of visiting Waterfall Gardens, a private park and Zoo in the Costa Rican mountains. We went there on a weekday and I knew we would find almost nobody there.
I have been honored to have a Black and White Photography Exhibition at the prestigious Calderón Guardia Museum in Costa Rica. Opening day on February 26 drew a large crowd of nice people and here are some snapshots from that night. Continue reading My Photo Exhibition in Costa Rica!→
When somebody asks me how to use a new camera my advice is always: set it in one of the auto modes and shoot away for a few days. Let it show you what it can do. Enjoy it.