Turrialba is the eastern-most of Costa Rica’s active volcanoes. A series of small explosive eruptions began there in January 2010, the first substantial activity at Turrialba since the 1860s. The 2010 explosions were presaged by the opening of small gas vents (fumaroles) beginning in 2006. A new vent, located on the southeastern flank of the volcano’s West Crater, opened on January 12, 2012.

According to the Observatorio Vulcanológico y Sismológico de Costa Rica, the new vent exhibited “a vigorous output of bluish gas at high temperature (T > 592°C) that generated a jet-like sound audible from the visitor lookout.” Activity since 2010 had been confined to a larger vent on the southwest flank of the West Crater, which continues to be the major source of emissions.

This image was acquired on January 21, 2012, by the Advanced Spaceborne Thermal Reflection and Emission Radiometer (ASTER) aboard NASA’s Terra satellite. The rock is very weak at the summit of Turrialba due to the intense rains of the region and the persistent hydrothermal activity at the summit. This means that new vents can open at the summit when pressure in the conduit is high enough to make its way through the weakened rock.

At 3680 meters and 3715 meters above sea level, respectively, the Payún Matru and Payún Liso stratovolcanoes are the highest points of the Payún Matru volcanic field of west-central Argentina. This astronaut photograph illustrates some of the striking geological features of the field, which is approximately 140 kilometers east of the Andes mountain chain.

The summit of Payún Matru is dominated by a roughly 15-kilometer wide caldera (image center), formed by an explosive eruption approximately 168,000 years ago. Several dark lava flows, erupted from smaller vents and fissures, are visible in the northwestern part of the field. One distinct flow, erupted from Volcan Santa María (northwest of Payún Matru), is approximately 15 kilometers long.

A number of small cinder cones – appearing as brown dots due to the short lens used – are built on older lava flows (grey) to the northeast. While there is no recorded observation of the most recent volcanic activity, oral histories suggest that eruptions were witnessed by indigenous peoples.