Rincón de la Vieja is one of those volcanoes that don’t make headlines with fiery lava streams and end-of-world scenarios. Presently, the biggest news from it are about yet another phreatic explosion, and the most exciting photos show a pale steam plume fading away, at best with a bit of ash mixed in. Moreover, the videos of ensuing lahars we have recently seen show some excited kids hopping about near the stream banks, watching the steaming hot water flow through the meadows. This all worries me a bit… it makes people placid and careless of danger. Because Rincón de la Vieja CAN do different.

Rincón de la Vieja is located in the Cordillera de Guanacaste mountain range, 25 km NNE of Liberia, the capital of the province of Guanacaste. It is also part of the Rincón de la Vieja National Park. The indigenous people of the Guatuso tribe named the volcano Rincón de la Vieja, which translates to English as “the old woman’s corner”. What exactly it was about is now forgotten but legends about a good (or a bad) old woman abound among the locals. – In the southern slopes of the volcano the Las Pailas Geothermal Power Plant has been constructed to produce 55 MW of geothermal energy,

 

OF PLATES & ARCS & IGNIMBRITES

Costa Rica is located on the southwestern margin of the Caribbean plate below which the Cocos plate subducts in a NE direction. There is an outer volcanic arc – a remnant of the island arc created during the subduction of the Farallon plate below the Caribbean plate. And an inner volcanic arc – the result of the later subduction of the Cocos plate below the Caribbean plate.

The inner arc is oriented NW-SE, parallel to the Middle America Trench. The Guanacaste volcanic chain is the NW end of the inner arc. It contains five major Quaternary stratovolcanoes and calderas. The voluminous silicic Santa Rosa ignimbrite plateau forms the basement of the mountain range. Later, the Rincón de la Vieja–Santa María volcanic complex was built upon the silicic Liberia formation – a product of previous caldera-forming events. Lava flows of andesitic to basaltic-andesitic composition are the first layers from Rincón de la Vieja.

 

THE VOLCANO

The Rincón de la Vieja volcanic complex consists of an arcuate NW-SE-trending mountain ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera. The complex has nine eruptive centers. The highest point is Santa María with 1916 m a.s.l., El Rincón de la Vieja cone is 1806 m and the Von Seebach cone 1.895 m high (the latter is named after a German Geologist in the 19th c.). Although the Santa María cone belongs to the group, it is considered a separate volcano.

 

THE ACTIVE CRATER “ACTIVE CRATER”

Volcanic activity has over time migrated to the SE, where the youngest craters are located. The presently active crater is aptly named Active Crater, at 1700 m located ENE of Von Seebach crater. A plinian eruption that produced the 0.25 km³ Río Blanco tephra about 3500 years ago was the last major magmatic event from it. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from this crater.

With its crater lake and fumarolic activity, Rincón de la Vieja resembles the Poas volcano in many aspects. The main difference is perhaps its greater risk of dangerous lahars due to the topography of crater and terrain.

An immense boiling pot…

There are at least three crater lakes in the Rincón de la Vieja volcanic complex. Additionally, Los Jilgueros lake which has no volcanic origins. The round-ish active crater lake of Rincón de la Vieja has a diameter of ~600m at the top edge. From observations in previous dry conditions the depth of the lake was known to be ~30m in 2010.

Under conditions of total mixing the lake has been described as an immense boiling pot loaded with material in motion. On many occasions spots of sulfur globules of various sizes were seen floating on the lake surface. Its colour varies enormously – from light blue (in periods of low fumarolic activity and little rain) over bright green to milky whitish, to an intense gray (in conditions of acute mixing by underwater activity, or by runoff from the high vertical walls).

The temperature ranges from 20°C to 58°C (measured since 1985). Due to the vertical walls of the crater basin and the abundance of gases over the lake, the monitoring conditions are often extreme: scientists must do the sampling from its edges or with appropriate climbing equipment.

…with a spout…

All of the topographic features surrounding the Active Crater are higher than its rim and are likely to prevent shallow ground water flowing away. Except to the north, where the Active Crater’s rim is lowest and its flank dips steeply and continuously toward the northern plains and Lake Nicaragua. All drainages along the north flank are tributaries for the Rio Cucaracho, which forms a 300-m-deep canyon 12 km NNE of the Active Crater.

Violent phreatic and phreato-magmatic eruptions have often driven the acid water out of the lake. As the northern edge is much lower than the rest, lahars followed one another in that direction. The liquid shot out like a geyser, hit the steep crater walls and en route collected any loose material in its path. With great speed it carryed the whole mess many km down the river beds of the Azul and Penjamo rivers and the Quebrada Azufrada. Lahar aprons are deposited at the base of the volcano, typically at elevations of 500-600 m.

…and leaky, too!

The northern crater walls are severely weathered. Deep cracks have developed, to the point that in the lower parts of the wall small fumaroles have appeared. Aquifers of such volcanoes undergo a process of infiltration – and therefore physical and chemical deterioration. Water geochemistry studies indicate that the crater lake water is indeed leaking through the edifice into the north flank drainages. As these walls consist mainly of  loosely consolidated tephra deposits this seeping water could weaken the already oversteepened north flank of the Active Crater. A potential sector collapse would be a severe threat to human lives and ecosystems.

Image left: Qualitative hazard map showing moderate- and high-risk zones for debris avalanches and lahars, originating from the Active Crater of Rincón de la Vieja. The greatest risk to lives, property and Nat’l Park land at the volcano is from northward-directed eruptions or sector collapse of the Active Crater. (Kempter et al., 2000)

Although the area is not densely populated a possible collapse with the then unavoidable flooding would put farmers and tourists, animals and plants potentially at severe risk.

Video: 7-minute video from 2015 by John Lizano via YT. It beautifully shows the large volcanic complex of Rincón de la Vieja with its various cones and lakes. The group hiked along the snail-shell like arcuate ridges to the main crater:

 

WATER & HEAT, ASH & MUD –
RINSE AND REPEAT

Rincón de la Vieja is an ever busy volcano. Even in the periods where no “eruptions” are stated, or even “inactivity”, there are reports of tremors, steam plumes, sulfurous smells, rumbling and hissing sounds, new fumaroles or mudflows. If we look at the many (58) GVP bulletins, starting in 1969, there was never really a pause in activity. Maybe in the 1970s (or could have just been not reported), and later in the 2000s.

From 1983 on, things got really turbulent, starting with a phreato-magmatic event on 6 February. It had ejected bombs, lapilli, and ash, as well as blocks 10-100 cm in diameter that formed impact craters. Strong rains eroded the ash and washed it into a ravine. This produced a mudflow in the Río Pénjamo, causing the deaths of thousands of fish – possibly because of the acidity of the water.

During a visit in 1985 volcanologists found evidence of another strong eruption – recently erupted material and a devastated area, both SE of the crater. “On 19 April there was a strong and constant emission of gas that affected breathing because of its acidity, and made it difficult to observe the lake in the active crater. …trees had been knocked down in a radial pattern by the activity. This pattern is unusual in that the fallen trees appeared to radiate from a point near their center, not from the crater.”

So it goes on until 1998 with more or less strong eruptions and restlessness of the volcano. A somewhat quieter period ended in 2011 and activity increased substantially in October 2015, when at least ten small to moderate phreatic eruptions were recorded.

Also, OVSICORI scientists reported in 2016 a change of the character of the deposits. The samples collected in February were rich in elemental sulfur, abundant in the crater lake and in the near-surface sediments. The March samples, however, showed the presence of clasts of altered rocks, hydrothermal minerals, less elemental sulfur as well as 3-10% fresh glass. That means that magma is near enough to the surface again to produce phreato-magmatic eruptions.

 

So – this is the state of Rincón de la Vieja at the moment. The last I have heard was of another phreatic explosion three weeks ago, on 3 March 2018. Otherwise the volcano is quiet; yesterday’s OVSICORI report stated that no eruption, no smell or ash has been detected.

Costa Rica has a system of volcanic activity levels from 0 to 5. The graphic on the right shows the level assigned to (some) CR volcanoes during the past 12 months. (OVSICORI-UNA). Click graphic or link below for complete list of all volcanoes. http://www.ovsicori.una.ac.cr/index.php/vulcanologia/nivel-de-actividad-volcanica

You may find any updates on OVSICORI’s FB page (I guess so, because I’m not on FB, as many others):
https://www.facebook.com/OVSICORI

Video:
Excellent presentation by OVSICORI, from 2017, 6 min:

 

CHEM TRAILS

Rincón de la Vieja is also one of the three Costa Rican volcanoes which pose the environmental problem of acidification. The fumes of acid crater lakes and volcanic degassing leave streaks of bare soil and withered or even totally burned vegetation (dead zone). Such trails develop over kilometers of land, mainly in the predominant wind direction from the crater, and may last for decades.

They occur by reaction of the gases with water on the plants’ surface, worsened by the presence of dust particles. The most damaging volcanic gas may be sulfur dioxide (S02). In smaller quantities, but corrosive and acid, hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He) play a role in this phenomenon. The most affected area on Rincon de la Vieja is of a triangular shape, the size about 2 km x 4 km to the west of the main crater. It is easily recognizable around the Active Crater, the Von Seebach cone and the steep western slopes.

 

RINCÓN DE LA VIEJA NATIONAL PARK

The 14,000-hectar park, with its highly active volcano and a fascinating ecosystem, is particularly appealing to hikers. Its mountain range with 32 streams separates the waters to the Pacific from those to the Atlantic Ocean. Las Pailas – the cauldrons – is the name of the western entrance to the Park. It is also the start of the 8 km hiking trail to Rincón de la Vieja. Boiling hot mud springs, sulfur springs, steam vents, and fumaroles are abundant. The area around the Las Pailas thermal anomalies has been identified as a small (5km) caldera by itself, the San Vicente caldera.

On the trails you also meet with breathtaking fauna and flora. Despite its special attractions, the Rincón de la Vieja National Park has largely been spared from the flow of visitors. Unfortunately, access to the upper parts of the volcano had to be closed in 2014 for safety reasons. Since that time, the hiking trail to the crater has become overgrown and practically lost in the jungle. Scientists who want to go up for volcanic surveillance now require the expert guidance of a local baqueano.

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Disclaimer: I am not a scientist, all information in this (and any of my other posts) is gleaned from the www and/or from books I have read, so hopefully from people who do get things right! 🙂 If you find something not quite right, or if you can add some more interesting stuff, please leave a comment.

 

Enjoy! – GRANYIA

 

SOURCES & FURTHER READING
– GVP, Rincón de la Vieja
– OVSICORI – any news would appear here on FB
– OVSICORI actual alert level of CR volcanoes
– OVSICORI two webcams Of R. de la V.
– […]Cañas Dulces caldera[…] (2000, paywalled)
– Leakage of Active Crater lake brine through the north flank […], and implications for crater collapse (2014, paywalled)
– Acidification Trails […] (2009, PDF)
– Costa Rica’s Crater Lakes (2010, PDF)
– Field Report of Visit to V. Rincón de la Vieja (2016, PDF)
– Rincón de la Vieja Nat’l Park
– VisitCostaRica.com
– plate-tectonic.narod.ru