Arenal volcano in Costa Rica is a youthful and vigorous stratovolcano, almost continually active since its current phase of activity began with a violent and deadly eruption in 1968. To quote the Global Volcanism Program’s Arenal summary, ‘Continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows has occurred since then from vents at the summit and on the upper western flank’.

The most recent instance of this type of activity was reported by the Observatorio Vulcanológico y Sismológico de Costa Rica (the inevitable acronym is OVISCORI) on 6 June 2008. A pyroclastic flow was generated on the south-western flank of Arenal when an accumulation of blocky, andesitic lava at the summit, the remnant of a March 2007 lava flow, collapsed. The flow descended some 800m, with pulverized material rising from it to produce a tall plume of gases and dust that provoked alarm in tourists and park officials The park was quickly evacuated and closed, no-one was hurt, and there was no further activity.

Bulletins on this activity (PDF) in both Spanish and English can be accessed from OVISCORI’s ‘Informes de Prensa’ page.

Arenal provides a fascinating case study in the ways human societies interact with and live alongside active volcanoes: its spectacular but largely safe activity attracts thousands of visitors, and it is at the heart of a national park that is one of Costa Rica’s main tourist attractions, while the lake at the foot of the volcano, Lago Arenal, has become the site of a large hydroelectric scheme that provides around 40% of the country’s electricity. Arenal.net, a travel-oriented site, offers a great deal of information about the volcano including maps, photographs and links.

UPDATE: There’s a report on what’s happened at Arenal, with some nice clear discussion of the science behind this kind of activity, over at Erik’s Eruptions blog.

Information
Global Volcanism Program: Arenal - volcano information for Arenal (1405-033)
OVISCORI - main page for the Observatorio Vulcanológico y Sismológico de Costa Rica

An analysis of gas collected from Turrialba volcano, Costa Rica, has revealed the presence of high proportions of helium in one of three samples collected on 7 and 8 March, according to a report in La Nación today. This suggests that magma may be building up within the volcano.

The gas sampling at Turrialba is being undertaken by a scientific team from the Observatorio Vulcanológico y Sismológico de Costa Rica (Ovsicori), part of the Universidad Nacional (UNA), while scientists at the Universidad de Costa Rica (UCR) have been carrying out the gas analysis. The UCR mass spectrometer analysis of the three gas samples revealed the presence of helium at a far higher level than normal: ‘We are talking about a difference of three orders of magnitude’ reports Jorge Andrés Díaz of the UCR.

Information
Smithsonian Institution Global Volcanism Program - summary information for Turrialba (1405-07=)
Observatorio Vulcanológico y Sismológico de Costa Rica - Ovsicori news page, including latest bulletins (which are in PDF format)
Volcán Turrialba - information from Ovsicori

News
Helio sugiere formación de magma en volcán Turrialba - La Nación, 9 April 2008 (Spanish)

Costa Rican scientists have identified a previously unknown volcano in the forests of San Carlos region, 90km north of the capital, San José. Infrared images taken as part of the joint US-Costa Rica CARTA 2005 mission in 2006 suggested the presence of a volcanic crater at a feature known as Cerro El Porvenir in an inaccessible part of the Parque Nacional del Agua Juan Castro Blanco. A ground expedition last week organized by the National Seismological Network at the University of Costa Rica, confirmed that El Porvenir is indeed a dormant volcano.

The volcano is conical in form and rises to 2,300 metres above sea level, with a 200-metre wide crater.

Information
Smithsonian Institution Global Volcanism Program - volcanoes of Costa Rica
Red Sismológica Nacional - National Seismological Network, Costa Rica

News
Hallado nuevo volcán en Costa Rica - Desdelesperpento (blog), 9 March 2008 (Spanish)
Científicos descubren nuevo volcán en el norte de Costa Rica - La Nacion, 8 March 2008 (Spanish)
Scientists spot previously unseen volcano in Costa Rica - Tico Times, 10 March 2008

Turrialba volcano, Costa Rica, began discharging gas and vapour on Wednesday 5 December 2007. The Observatorio Vulcanológico y Sismológico de Costa Rica reported that by 05:40 local time (11:40 GMT) on 5 December a 2km column of gas and vapour was visible. The volcano, which is 40km east of the Costa Rican capital San José and overlooks the city of Cartago, last erupted in 1866. It has been subject to close observation since an increase in seismic and fumarolic activity in May 2007.

Information
Smithsonian Institution Global Volcanism Program - summary information for Turrialba (1405-07=)
Observatorio Vulcanológico y Sismológico de Costa Rica - news page, including latest bulletins (which are in PDF format)
Red Sismológica Nacional, Costa Rica - Turrialba image gallery

News
Costa Rica volcano begins spewing gas, vapor - Inquirer.net, Philippines (6 Dec 2007)
Turrialba volcano acts up - Tico Times, Costa Rica (6 Dec 2007)
Dormant volcano in Costa Rica began discharging vapor and gas - AHN (6 Dec 2007)