Posted on behalf of Patricio Segura in Chile.
Chile’s Hudson volcano (Cerro Hudson) awoke from a twenty-year slumber on Wednesday 26 October and is now pouring smoke and ash high into the sky, threatening a major eruption.
The stratovolcano, in the Aysén Region of northern Patagonia, is enormous. Standing 1,905 metres high, its caldera forms an ellipse about 10 kilometres long and 5 kilometres wide.
Three columns of white steam are now rising from a melting glacier that covers the volcano, following a tremor that was felt as far away as Puerto Aysén, a small town of 20.000 inhabitants some 65 kilometres north. (see BBC)
Chilean authorities yesterday declared a red alert, and evacuated roughly 130 inhabitants living in a 50 kilometre radius around the volcano (four farmers who did not want to leave their homes remain inside the evacuated area). Ash was already beginning to fall on the town of Puerto Chacabuco, about 50 kilometres north of the volcano.
Today, Mount Hudson grew more active and is causing about five tremors every hour. Geologists believe that a major eruption could occur within the next hours or days, and are monitoring the volcano via six remote seismic stations, and making regular observation flights.
Patagonians are worried. Many remember Mount Hudson’s catastrophic eruptions of 1971 and 1991. The latter eruption was one of the most violent registered eruptions in Chile, and lasted for five months. At its peak it turned day into night, making the banks of nearby Huemules, Cupquelan and Ibáñez Rivers collapse with ash. Many areas in the region are still covered with ash, pumice and other volcanic rocks. “These are the characteristics of this highly explosive volcano,” said Juan Cayupi, a volcanologist at the National Emergency Office.
According to the National Geology and Mining Service, nearby rivers risk being destroyed if rock, ash and melting ice combine to create powerful mudslides called lahars, which can sweep away anything in their path. Pyroclastic flows – bursts of rock and gas – could also cause extensive damage.
Authorities are worried that they may have to deal with destroyed roads, livestock deaths, floods, water pollution, and the suspension of airline flights in the region. Gas masks were distributed to local citizens today. Mount Hudson’s violence could even reach Argentina’s Santa Cruz province, as happened in 1991, when it affected a 150,000 square-kilometer area between Chile and Argentina. Today, the plume is still growing, and heading towards the town of Coyhaique 75 kilometres away, where some of its 50,000 inhabitants are preparing for the worst.
The Hudson volcano stands on the Liquiñe Ofqui Fault Zone (LOFZ), which crosses Chile from north to south for 1,100 kilometres, and was responsible for the eruption of the Chaitén volcano in May 2008. The Puyehue-Cordón Caulle Volcanic Complex, also resting on the LOFZ, has also been active since June this year. The LOFZ also caused the Aysén Fjord earthquake in April 2007, which generated a tsunami that killed 11 people.
Luis Donoso, a geophysicist at the University of Chile, Santiago, says that during the 1991 eruption, Hudson ejected more than 4 cubic kilometers of tephra (volcanic rock) and 1.5 million tonnes of sulphur dioxide gas.
A local newspaper reports today that glaciologists flew over Mount Hudson in August, and found thermal anomalies, melting ice and fissures. “The question now is why the local authorities and residents did not have this information. One possible explanation is the long and fuzzy decision-making path from the technical services to the authorities," says Donoso. "The time to build up a new national geosciences service is now.”
Photo: Antonio Horvath Kiss