Volcanic Hazard – Volcano Activity (Eruptive Phase): Turrialba Volcano, Costa Rica
Central America – Costa Rica | Province of Cartago, Cordillera Central, Turrialba Volcano
Location: 10°01’00.5″N 83°46’03.8″W
Stratovolcano: 10,958 ft (3,340 m)
Status: eruption warning
Friday May 20, 2016, VolcanoDiscovery
The activity at the volcano has increased during the past days and ash emissions from the active crater with intermittent stronger explosions have been near-continuous since yesterday.
A more violent phase of explosive activity began this morning at 07:29 local time, producing an ash column that rose about 3000 m above the crater to approx. 20,000 ft (6 km) altitude.
The most energetic phase lasted about 6 minutes and produced pyroclastic flows from collapsing parts of the ash column that affected the central crater and eastern rims.
An ash plume drifted eastwards and caused moderate to light ash falls in up to 60-70 km distance. A strong smell of sulfur was reported by eyewitnesses from various towns including San Rafael and San Francisco (50 km ENE).
Following similarly strong explosions yesterday afternoon (at 15:47, 16:09), the preventive exclusion zone was extended to a radius of 5 km around the crater. The school in the hamlet of La Central at the SW foot of the volcano remained closed.
After the strong explosion of 12 May, the volcano had been relatively calm for several days. In the evening of 17 May, seismic activity increased, first the number of long-period earthquakes and later volcanic tremor became stronger. Weak ash emissions started in the morning of 18 May, and became near-continuous after 11:04. Activity notably increased at 11:48 and a small explosion, which lasted 10 seconds and ejected ballistic blocks towards the crater rim, occurred at 12:56. This first new eruptive phase decreased at 14:30.
A second eruptive phase occurred yesterday morning at 07:27 and lasted approx. 6 minutes, generating pyroclastic flows that traveled to the central crater and the northern rim. Activity, at fluctuating levels, has been continuous since.
According to RSN, the current behavior of Turrialba is “entirely normal” for a volcano that is entering a new eruption. So far, monitoring data suggest that it involves a probably small batch of fresh magma that has risen to shallow depths (about 1 km) beneath the surface. The current explosions are likely the result of interaction of this magma (and its gasses) with the superficial hydrothermal system.
How the eruption will evolve is unknown, but two scenarios are considered most likely:
1. The activity continues at similar levels and evolves into a state where the conduit is open, allowing rapid degassing and rise of the new magma. This might translate in intermittent to continuous explosions of stronger size than now, producing ash columns up to about 5 km tall, such as were observed during the last historical eruption of the volcano in the 19th century.
This type of activity would likely only severely threaten areas up to 2 km away (ballistic ejecta, pyroclastic density currents). Ash fall is likely to affect mostly areas south and west of the volcano due to the prevailing northerly and easterly wind directions.
2. A second scenario is that the volcano’s activity decreases, if the magma body is not large or gas-rich enough to reach the surface. Activity might gradually calm down and the volcano could fall back to dormant state.
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