Chile monitors volcanic field after seismic swarm causes 160 quakes in 2 hours

SANTIAGO (Reuters) -A seismic swarm that caused 160 quakes in two hours at the Laguna del Maule volcanic field in central Chile earlier this week has put authorities and citizens on alert.

The volcanic complex, located about 300 km (190 miles) south of the capital near the Argentine border, is a vast 500 square km (193 square miles) area with volcanic domes, cones and lava flows with an estimate 130 volcanic vents.

"These are signs that the volcano is active, it has magma, what's inside is moving and this can lead to a moderate-sized event in the future," said Ayaz Alam, a geologist and professor at the University of Santiago of Chile. "But when? We don't know."

Chile's National Geology and Mining Service, Sernageomin, said the quakes were low magnitude and kept the volcanic complex on green alert, meaning there was no immediate risk. Chilean disaster agency Senapred said it would continue working with regional authorities to alert and respond to any eventual emergencies.

Alam said seismic swarms in volcanic areas are lower intensity and different from swarms along fault lines because the activity is caused by magma flows rather than tectonic plates crashing into each other.

The largest tremor registered during the swarm was a 2.1 magnitude but the relatively young volcanic field has shown several signs of activity in recent years

Daniel Diaz, a geophysicist and volcanologist at the University of Chile, says the area is quite unique since it doesn't have a single volcanic structure, but dozens around the lake, some of which have formed in the last 2,000 years.

"This (volcanic) system is quite recent and therefore we expect there to be activity," Diaz said. "But it's not concentrated in one structure or cone, but all around the zone surround the Laguna del Maule."

(Reporting by Jorge Vega and Reuters TV; Writing by Alexander Villegas; Editing by Lincoln Feast.)