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Earth of fire

Actualité volcanique, Article de fond sur étude de volcan, tectonique, récits et photos de voyage

 

In the series " Volcano observatories and volcanoes associated"  whe opened a few months ago , add one of Costa Rica: the OVSICORI - UNA .
 
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The Observatorio Vulcanológico y Sismológico Costa Rica - Universidad Nacional exist under this name since 1986. He is in charge , in addition to seismic and tectonic research, of the surveillance , among the 116 volcanoes in Costa Rica, of six active volcanoes ( Arenal, Irazu , Miravalles , Poas , Rincon de La Vieja , Turrialba ) and 2 sleeping ( Barva , Orosi ) , divided into three mountain ranges : the Guanacaste , the Tilaran and central Cordillera .

All of andesitic type, they owe their formation to the subduction of the Cocos tectonic plate under the Caribbean plate , forming volcanoes of continental margin.

schémas 008 copie
         Tectonics of Central America - with involvement of Cocos and Caribbean plates in Costa Rica

The buildings of the Observatory are located in Heredia, about ten kilometers from the capital San Jose. During a visit in 2008, I had the opportunity to visit the facilities along with Rodolfo van der Laat , engineer and surveyor volcanologist in OVSICORI .

 

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                         The front of the Observatory Heredia - photo Bernard Duyck

 

costa Rica 217       Rodolfo van der Laat when visiting the OVSICORI, in behind the scenes - photo Bernard Duyck
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OVSICORI - Side facing the battery of Sismos , the two darkest plots are for Arenal, top left and Poas , bottom center - photo Bernard Duyck

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Spy games to OVSICORI - the chart of the evolution of earthquakes marking the Turrialba in 2007-2008 strongly interested me - photo Jean- Michel Mestdagh

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With Tanguy de Saint Cyr at the Arenal Observatory , the volcano was invisible that day in the remnants of a tropical storm - photo Bernard Duyck

Volcanoes have been analyzed and processed separately , I will briefly mention that their current status. ( Annual Report OVSICORI )

In alphabetical order:

The Arenal : Its last eruption dating back to the 14th century , popular memory had forgotten his danger before his rude awakening in 1968 , which killed 90 people. Regularly active since then, he calmed down in December 2010. He present since more than three years a low seismic activity and fumes mainly of water vapor at craters C and D. Levels of SO2 in the gases are at the limit of detection level of sensors and the fumaroles temperatures measured by infrared thermography exceeds 180° C.

2013.09.08 - Arenal - Jason Cordero S. - RSN
Arenal -  09/08/2013 - some fumaroles in the clouds to remind us that the volcano is still "active" - photo RSN

Irazu Volcano : the volcano- tectonic seismicity remained at a low level compared to previous years. The main crater remained mostly dry throughout the year , not allowing the installation of a new lake.

2013.09.07 - Irazu - Brandon Arias Ramírez - RSN
Irazu - Crater activo - the acid lake disappeared - the 09/07/2013 - photo RSN / Brandon Arias Ramirez

For Poas , the seismicity remained at a stable level. Phreatic eruptions at the laguna Caliente were recorded between 4 and 9 months eruptions . The lake level has varied in amplitude zone of 2.5 meters during the year, the average annual temperature of acid lake is 45-50 ° C and a pH of 0-0.3 . At the superficial level, gas concentration seems stable,   fumaroles temperatures fluctuating between 100 and 600 ° C, with a maximum between April and July.


2013.08.06 Poas éér.phréatique - Paulo Frutos Porras - R
                 Poas - phreatic eruption on 06/08/2013 - photo Paulo Frutos Porras

In 2013, the active convection cells marked the warm and acid Rincon de La Vieja's lake . Fumaroles were measured at a temperature reaching 130° C on the west wall of the active crater .

 The physico-chemical characteristics of the lake acid are similar to those observed in 2000 and suggest that during the past decade, a substantial amount of magmatic gas was injected into it.

2013.02.26 Rincon - involcan
            Rincon de La Vieja - 26.02.2013 - active crater and its acid lake - Photo Involcan

In Turrialba , the year began with a similar seismicity to the previous year. From March to April, the volcano- tectonic earthquakes were recorded at a depth greater than 5 km. below the summit of the volcano, and the first type tornillo earthquakes .

 On May 21 , a sudden decompression accompanied by ejection of tephra through the 2010 and 2012 vents was accompanied by seismic activity and indices typical CO2/SO2 . On July 13, the number of earthquakes increased to 500 per day and remained at these values ​​until the end of August , before declining . During this period , temperatures measured at the mouth in 2012 ranged between 600 and 800° C. In November , seismicity leaves suggest a change in the composition of fluids. Since decompression in May SO2 flow was maintained at a low value , of the order of 500 to 1000 tonnes / day.


2013.05.21 Turri - F.Chavaria Kopper Ovsicori                
Turrialba - the 21/5/2013 - photo F.Chavaria Kopper / OVSICORI

 

 

Sources :

OVSICORI - UNA - rapport annuel - link

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