Turrialba’s unwelcome emissions 26 April 2009Posted by admin in activity reports, Costa Rica, natural hazards, Turrialba.
Tags: Central America, Costa Rica, natural hazards, Turrialba, volcanic activity reports
Turrialba volcano in Costa Rica, a massive 3340-metre high stratovolcano, has been quiescent since a series of explosive eruptions in the mid-nineteenth century. The last eruption sequence lasted from August 1864 to February 1866, ending with a VEI=3 event producing pyroclastic flows, lahars and thick ashfall. There have been no further explosive eruptions but seismicity began to increase in the late 1990s and fumarolic activity became more pronounced in the early 2000s. The threat of renewed explosive activity remains.*
The main hazard Turrialba is presenting at the moment, however, is a non-eruptive one. As part of the generalized upswing in activity over the past few years, levels of sulphur dioxide in the volcano’s emissions increased greatly, reports the USGS, from around 140 tonnes/day in late 2007 to 1100-2000 tonnes/day in summer 2008. The most recently available figures on Turrialba’s SO2 flux come from the 4th Ticosonde Workshop (PDF) held at Costa Rica’s Universidad Nacional on 26 March 2009: a presentation by Dr Sebastián Miranda of the Observatorio Vulcanológico y Sismológico de Costa Rica (Oviscori) reported that emissions have recently shown a decline, with an average SO2 flux for the period December 2008 to February 2009 of 250 tonnes/day.
This recent decline notwithstanding, Turrialba’s SO2 emissions have had a dramatic effect on local vegetation. Sulphur dioxide is damaging to plants in high concentrations, but the effects of long exposure to even relatively low concentrations are potentially much more destructive. causing growth reduction, burning and damage to foliage (foliar necrosis) and yellowing due to a lack of chlorophyll (chlorosis). Vegetation situated below a persistent SO2-rich volcanic plume will be severely affected, while acid rain generated by the SO2 concentrations may spread the damage even further.
An article in the Costa Rican newspaper La Nación today makes it clear how serious the problem is. Headed ‘Daños por volcán Turrialba ganan terreno este año’ (‘Damage from Turrialba volcano gains ground this year’) it describes the severe problems the persistent exposure to the volcanic emissions has caused. Javier Coto, who farms land near Turrialba, reports that ‘today we have only dry grass. Here everything is bad. The barbed wire fences crumble and the iron roofing rots away’. Workers at a nearby dairy wear masks to help them cope with the ‘almost unbearable’ sulphurous smell of the gases, and the burning of pastures affects milk production. The area affected by Turrialba’s emissions has expanded, according to Ovsicori scientists, increasing the impact on local agriculture:
In the areas closer to the mountain, the damage caused by the burning ‘is irreversible’, says scientist Eliécer Duarte of Oviscori. ‘In the area of the summit of Cerro San Juan (near the crater of Turrialba) all the vegetation is totally dead. Shrubs that have shown little effect on other occasions … are today completely burned on their surface and into the wood. Small plants, shrubs and trees of low habit are covered with a fine coating of sulphur.’
Wind patterns and the effects of the increase in emissions are responsible for the greater degree of damage this year, say experts from Ovsicori.
Meanwhile, the most recent studies of Turrialba by the Costa Rica National Seismological Network indicate increased seismicity, with a growth in the numbers of hybrid and superficial volcano-tectonic earthquakes being recorded, El Azucarero reported this week.
* For a clear overview of Turrialba’s eruptive history and hazard potential, see M. Reagan, E. Duarte, G. J. Soto & E. Fernández, ‘The eruptive history of Turrialba volcano, Costa Rica, and potential hazards from future eruptions’, in William I. Rose, Gregg J. S. Bluth, Michael J. Carr, John W. Ewert, Lina C. Patino & James W. Vallance, Volcanic Hazards in Central America (Boulder, CO: Geological Society of America, 2006), pp. 235-57.
Daños por volcán Turrialba ganan terreno este año – La Nación, 26 April 2009
Geólogos detectan incremento sísmico en el Volcán Turrialba – El Azucarero, 24 April 2009
Global Volcanism Program: Turrialba – summary information for Turrialba (1405-07=)
Observatorio Vulcanológico y Sismológico de Costa Rica – Ovsicori website
Volcán Turrialba – information from Ovsicori