Santiam Pass reopened Friday afternoon after avalnches and heavy snow closed Highway 20.

 Slideshow: Photos of snow-covered Oregon passes

Crews planned to set off explosives on Friday, to trigger more slides and then clear them off the roadway.

Chains were required for cars and large trucks, but 4X4s and cars with studs were exempt.

Dangerous snowslides closed the section of Santiam Pass early Thursday morning. ODOT also asked truckers to hold of driving until the storm was over. Highway 20 reopened Friday afternoon with a chains requirement for all vehicles.

ODOT said more conditional closures were likely, if conditions worsen as expected.

 Map: Closures

Joe Harwood, with the Oregon Department of Transportation said there were "multiple" snow slides on the pass and conditions were dangerously unstable.

“There are blizzard-like conditions up there and we still have a very unstable snowpack above the highway,” Harwood explained. “We’re not going to reopen the highway unless we’re sure those slides are not going to come down."

 More: Travel conditions

Check Santiam Pass live cam

"ODOT crews with snow blowers and snow plows are removing the slide debris that came down this morning, but it is snowing so hard that as soon as crews clear a lane, it quickly becomes snowed-over again. High winds are also blowing massive amounts of snow onto the highway," Harwood said.

 Snow business: Snow removal budgets stretched thin

Harwood added that ODOT would use explosives to trigger slides if they have to, in order to clear the unstable snow and ensure drivers' safety.

Multiple snow slides tumbled onto roadway

Early Thursday morning, heavy snow broke loose in rising temperatures and smashed down on the highway in several spots between mileposts 75 and 80. Two semi-trucks were stuck in between slides and ODOT crews had to carve out a lane so they could safely drive out.

OSP

Luckily, no vehicles were hit by the slides and no injuries were reported.

However, around 40 semi-trucks were stranded on the pass, and drivers forced to just park and wait because there was not enough room to turn the large vehicles around. To make matters worse, Harwood said those semi-trucks were "inhibiting ODOT's ability to clear snow."

Just outside Salem and Sisters, ODOT posted signs warning drivers not even to venture toward the pass, in an effort to ensure that more vehicles don't get stranded.

Detroit covered in deep snow

One the edge of the closure in the small town of Detroit, heavy snowfall has isolated the community and the mayor was calling for emergency assistance. Since December 1, 150 inches have fallen in the town with about a foot coming down everyday for the past few days.

 More: Heavy snow covers Detroit, Ore.

A backhoe in town worked to push snow away from the street, building snow piles 10 feet high in spots. That was also causing some problems with power, since trees have collapsed onto power lines.

Dangerous avalanche on Snoqualmie Pass

In Washington state, a large snow slide on Snoqualmie Pass buried three cars, but no one was seriously injured there, either.

 Also: Avalance buries cars on Snoqualmie Pass

Washington state transportation officials said the avalanche one of the largest on Snoqualmie since 1975 and heavy snowfall combined with warmer temperatures was creating "ripe conditions" for avalanches.

The National Weather Service issued a Snow Advisory for the Northern Oregon Cascade foothills and the Cascade Foothills. Cities in the advisory include Sandy, Silver Falls State Park, Sweet Home and Cottage Grove. The snow advisory was expected to remain in effect until noon Friday.

NWS meteorologists said snow levels will mainly be above 2,500 feet Thursday morning but will begin lowering to around 2,000 feet by late in the afternoon.

Snow levels will continue lowering to 1,500 feet tonight and Friday. Snow accumulations of four to eight inches are possible tonight with the higher amounts at or above 2,500 feet.

Problems in Eastern Oregon, too

Additional snowfall of around three to five inches is likely Friday.Eastern Oregon was also seeing its share of problems; ODOT closed I-84 between La Grande and Baker City Thursday morning, due to high winds, blowing snow and white-out condition.

 Also: Snow-covered mountains could cause extreme floods

Five rescued after van trapped in heavy snow

Elsewhere, I-5 on the Siskiyous Pass was closed to all traffic due to heavy snow.

Southbound I-5 is closed at Ashland and northbound I-5 traffic is being held back at Yreka, California. ODOTs Dave Thompson estimates, pending weather conditions, that I-5 will remain closed until 5 p.m.

In Central Oregon, Highway 140E from Adel to Nevada border remained closed; Highway 62 (Ft. Klamath to Crater Lake) remained closed; and Highway 70 from the junction with Highway 140 to Bonanza was closed.

In Northeast Oregon, I-84 was closed between Pendleton and Ontario; Cove Highway (OR 237) was closed between Island City and Union; Joseph - Imnaha Highway (OR 350) was closed between mile point 0 and 8. This was all due to high winds, blowing snow and white-out conditions.

Motorists traveling through the areas under advisory were warned to expect severe winter weather with packed snow, spots of ice and limited visibility in many areas.