A vast cloud of ash spewing from a Chilean volcano disrupted air travel across much of South America, while heavy rains around the eruption site prompted fears of mudslides.
Air traffic was sharply curtailed on the continent as the ash cloud drifted over Argentina, Uruguay and into Brazil. Flights in and out of the Argentine capital Buenos Aires, a key regional hub, were canceled for most of the day.
Rain mixed with volcanic ash poured down on communities near the Puyehue volcano, raising fears that the weight of falling water and volcanic materials could cause mudslides and threaten dams in the area, some 870 kilometers (540 miles) south of the capital Santiago.
A milky coating of ash settled on the waters of Gol Gol river, which was swollen by heavy rains.
"We are concerned about water that can drag the volcanic material certain places and cause some dams to fall," Public Works Minister Hernan de Soliminhac said.
Enrique Valdivieso, director of Chile's National Service of Geology and Mines (Sernageomin), said heavy rains would not quell the power of the volcano but could bring gases and ash to the surface, contaminating nearby rivers.
Valdivieso said Puyehue's eruptions have slowed but there is still a risk of large amounts of sediment pouring down from the eruption.
Across the border in Argentina, residents were without electricity or drinking water in the winter resort of Bariloche as a torrent of mud and volcanic ash wreaked havoc.
The problems were worsened by heavy rains that mixed with ash and caused power generators to short circuit, creating more havoc.
"I came with my family the day of the eruption. Since then I can't understand what is happening," said Augusto Reales, a tourist from northern Argentina, as he boarded a bus to leave the resort area. "We can't stay with so much uncertainty."
On Lake Nahuel Huapi, one of Bariloche's main tourist attractions, the emerald green waters were covered with patches of black ash.
"The eruption has begun to lose power but the active phase of the volcano is going to last for weeks or months," said Gustavo Villarosa, a volcanologist.
The price for face masks surged in several days to the equivalent of eight dollars, prompting warnings from local officials.
But the main worry for Bariloche was the closure of its airport -- its runways blanketed with a thick coat of ash -- just ahead of the ski season, the big draw for the local economy.
Brazilian officials said meanwhile the volcanic cloud had moved over the southern states of Rio Grande do Sul and Parana.
The cloud is crossing Brazilian territory "in the upper atmosphere," said Saulo Freitas at the Brazilian Institute of Space Research.
He said the cloud is likely to continue toward the Atlantic coast at an altitude of 8,000 to 12,000 meters (26,000 to 40,000 feet).
So far 4,000 people have been evacuated from 22 rural Chilean communities surrounding the Puyehue volcano, which rumbled to life on Saturday after showing no activity since 1960, when it erupted following a magnitude 9.5 earthquake.
A total of 62 flights were canceled Tuesday at the two airports in the Argentine capital but aviation officials in Buenos Aires said flights were being rescheduled.
"Flights in and out of Argentine destinations are being restored little by little," said the Chilean carrier LAN.
Around 90 percent of flights into Montevideo were canceled, and other flights from Brazil and Chile crossing over the affected area were scrapped due to fears of volcanic ash that could damage jet engines.
Airports in southern Argentina have been closed since Saturday's eruption of the volcano in neighboring southern Chile.
The eruption forced Bariloche, population 150,000, to declare a state of emergency Saturday and close its airport.
It also forced a major border crossing to close due to low visibility, and dropped ash on the upscale Argentine resort town of Villa La Angostura.
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