JUNEAU -- The sound of artillery fire that legislators sometimes hear when they're walking into the Capitol building in Juneau is the government defending the city.
In this case, it is crews using a 105 mm howitzer to try to prevent the kind of avalanches that recently buried the Richardson Highway and cut off Valdez from the state's road system.
In Juneau, the danger is to Thane Road, where deadly avalanches have in the past separated some residents from town. Avalanches can also cut the city off from access to most of its hydroelectric power.
To release those avalanches before they become major dangers, a volunteer gun crew uses a howitzer on loan from the U.S. Army to trigger a series of small avalanches at a designated time.
Greg Patz, Southeast maintenance superintendent with the Alaska Department of Transportation and Public Facilities, has what may seem to be an unusual description for an artillery barrage.
"It's a very much a precision instrument, with intricate instrumentation," he said.
That precision is used to release large masses of snow by using 20 or more shots, moving from bottom to top, releasing massive amounts of snow a little at a time.
The howitzer is fired from Douglas Island, across Gastineau Channel, into the hillside above Thane Road south of downtown.
While similar gun crews do avalanche control work in Alaska and elsewhere, its unusual to have them so close to a city, Patz said.
Patz said the shell placement is so precise that the gun crews can tell exactly where the shells will land. What's even better, they don't even need to be able to see what they're shooting at. That means the cannon avalanche control can be used in weather that would ground aircraft.
Until recently, the alternative to the howitzer was dynamite dropped out of helicopters.
Now, Juneau-based Alaska Electric Light & Power uses a newer technology, a gizmo called a "DaisyBell" that's slung beneath a helicopter, said Scott Willis, the utility's generation engineer.
Under the bell is pumped a mixture of hydrogen and oxygen that can be blasted from the helicopter.
"It's makes a concussion, kind of a boom out of the bottom of that bell," he said. "You can create your own mini-avalanche."
That replaced the old method, which AEL&P used until recently.
"It's much more precise than throwing dynamite out of the helicopter," Willis said.
Its also considered to be safer, more effective and involves fewer federal permits.
"It's worked very well for us," he said.
The DaisyBell explosions can be used to "nibble" away at threatening snow loads hanging over the city, reducing danger to the public and to infrastructure.
That method is used in more remote areas, where the DOT can't aim its howitzers.
In Juneau, avalanches are a big deal. Twice in recent years Juneau has been cut off from its hydroelectric dams for weeks at a time, forcing a switch to diesel generators and driving power rates through the roof. Unlike Valdez, however, getting cut off from the road system isn't a concern in Juneau. While the state's capital is on the mainland, it is the largest city in Alaska not connected to the road system.
Still, avalanches have long been a threat in snowy Juneau, and 20 years ago a Highway Division equipment operator was killed on Thane Road when he was clearing one avalanche and another came down the mountain.
The cannon shots are just one part of a comprehensive avalanche control program. DOT built diversion structures along Thane Road to provide some protection for travelers. Recently, avalanche cams have been installed to monitor the area.
Juneau's power lines have also received protection. Some of those along Thane Road have been buried, while avalanche diverters have been built to protect the most vulnerable of the city's transmission lines.
Contact Pat Forgey at pat(at)alaskadispatch.com