Massive avalanches destroyed transmission lines and support towers to a dam that supplies 85 percent of the electricity for Alaska's capital, and utility rates could quintuple for months until repairs are made, officials said.

The series of avalanches hit at 4 a.m. Wednesday, taking out 1.5 miles of power transmission line and destroying or severely damaging five support towers along a steep mountainside outside the Snettisham Hydroelectric Facility, about 40 miles from downtown Juneau.

Diesel generators were running Wednesday morning and are expected to continue to supply most of Juneau's power needs for the next three months, albeit at a much higher cost than the 11 cents per kilowatt hour paid for hydropower-generated electricity.

"We've always known that the Snettisham line was vulnerable because of the location of those hydro projects and that long transmission line, so we've always had a contingency plan," said Alaska Electric Light and Power president and general manager Tim McLeod.

One in five households in Juneau are heated with electricity, according to the city.

"We are very mindful of the fact that this disruption of power will affect every household and business, and for businesses and families that are operating on the margins, this will have a profound consequence," said Juneau Mayor Bruce Botelho at a news conference Thursday.

The financial impact on public, private and commercial properties will total about $25 million, according to the city, which issued an emergency declaration asking for state assistance. It included a request to seek federal help.

"It's not to help AEL&P replace power lines but relief for citizens, relief for fuel costs," said city manager Rod Swope, who also warned that assistance, even if it's granted, won't be available for months.

Repairing the line is estimated to cost $5 million to $10 million, said McLeod, but conditions are too unstable at the site to assess the situation from the ground.

City offices have already begun implementing conservation measures, and some power-starved facilities may have to reduce their hours, said Swope.

Marie Darlin, who lives in senior housing, said residents and management are turning off lights and tightening their belts.

"I think they are all just trying to figure it out," said Darlin. "We pay our own electricity and we are going to feel it."