Police close off the road leading to the Poas National Park and Poas Volcano

Q COSTA RICA – For the last couple of years our attention has been focused on the Turrialba, the volcano that has spread its ash and gases across the Central Valley and even forced the closure of the San Jose international airport on several occasions.

But, today, the focus is on the Poas.

On Wednesday night, the Poas Volcano registered a new phreatic eruption*, causing the Desague river to overflow after a head water flowed from the colossus, confirmed the Observatorio Vulcanológico y Sismológico de Costa Rica (Ovsicori) – the National Volcanological and Seismological Observatory.

The explosion Wednesday night reached up to one of the guardrails located at the outlook point where hundreds of tourists daily take in the breathtaking view of the volcano’s crater. Photo Facebook Ovsicori- UNA.

The eruption occurred between 6:00pm and 7:00pm. Park rangers reported a great amount of ash flowing into the Toro Amarillo river.

Not to be upstaged, the Comisión Nacional de Emergencias (CNE) – National Emergencies Commission – reported the a presence of high flow of gases and aerosol from the Turrialba.

Back to the Poas.

Following last night’s eruption, the Sistema Nacional de Áreas de Conservación (Sinac) – National System of Conservation Area – activated the emergency protocol, that includes the Poas Volcano National Park not open to tourists for today, Holy Thursday.

The Sinac said the Park will be closed waiting on the scientific-technical reports on what happened.

Walter Fonseca, of the Operations Unit of the CNE, said that the CNE experts continue the monitoring the volcanoes in conjunction with the Ovsicori and the National Seismological Network (RSN) of the University of Costa Rica (UCR).

He added that the Emergency Committees of Poás and Valverde Vega are activated and in constant communication with the CNE.

 

Also experts of the CNE will visit in the next hours the Toro Amarillo, with the intention of quantifying the possible affectation.

The Poas Volcano

The Poas is an active 2,708-metre (8,885 ft) stratovolcano located northwest of the greater metropolitan area of San Jose (GAM). It has erupted 39 times since 1828 and is one of 9 volcanos currently monitored by the Deep Earth Carbon Degassing Project. The project is collecting data on the carbon dioxide and sulfur dioxide emission rates from subaerial volcanos.

Crater lakes

There are two crater lakes near the summit. The northern lake is known as the Laguna Caliente (“hot lagoon”) and is located at a height of 2,300 m in a crater approximately 1.7 km wide and 290–300 metres deep. It is one of the world’s most acidic lakes. The acidity varies after rain and changes in volcanic activity, sometimes reaching a pH of almost 0; consequently, it supports little or no aquatic life. The bottom of this lake is covered with a layer of liquid sulfur. Acid gases create acid rain and acid fog, causing damage to surrounding ecosystems and often irritation of eyes and lungs.

Lake Botos, the southern lake, fills an inactive crater, which last erupted in 7500 BC. It is cold and clear, and is surrounded by a cloud forest located within the Poás Volcano National Park.

Eruptive history

Poás was near the epicenter of a 6.1-magnitude earthquake in January 2009 that killed at least forty people and affected Fraijanes, Vara Blanca, Cinchona (the most affected area), San José, and the Central Valley.

There was also eruptive activity in 2009 involving minor phreatic eruptions and landslides within the northern active crater. Poás eruptions often include geyser-like ejections of crater-lake water.

On February 25, 2014, a webcam from the Ovsicori captured the moment a dark cloud exploded about 300 metres in the air from a massive crater of the Poás Volcano.

The other volcanos, in addition to the Poas and Turriala, in Costa Rica are:

  • Arenal, an active andesitic stratovolcano located in La Fortuna, 90 km northwest of San Jose. The volcano was dormant for hundreds of years. In 1968 it erupted unexpectedly, destroying the small town of Tabacón
  • Barva  (Last eruption was in 6050 BC)
  • Irazú, an active volcano close to the city of Cartago
  • Miravalles, is an andesitic stratovolcano, it reaches an elevation of 6,653 feet (2,023 m) and is the highest mountain in the Guanacaste Mountains. 
  • Orosi (Inactive)
  • Rincon de La Vieja, is an active andesitic complex volcano in north-western Costa Rica, about 25 km from Liberia, in the province of Guanacaste.
  • Tenorio

*A phreatic eruption is a steam eruption without lava ejection. Phreatic eruptions are a common precursor of volcanic activity. The eruptions are caused by groundwater flashing to steam as it is heated by magma.