Temporary fix in place for Spenard sinkhole that closed part of Benson Boulevard

A big sinkhole that closed part of Benson Boulevard on Thursday night was temporarily fixed by Friday morning.

But the Alaska Department of Transportation still needs to find out what caused the 15-foot deep "chasm" to open up in the first place, a spokeswoman says.

The sinkhole closed the northernmost — or left — lane of Benson between Lois Drive and Minnesota Drive on Thursday evening. A second lane was closed for a time as repairs proceeded.

State crews used stockpiled recycled asphalt pavement to fill the hole, DOT spokeswoman Shannon McCarthy said. A more permanent fix will still be needed, once the cause of the problem is found.

McCarthy estimated the gap, unofficially dubbed "Sink hole de Mayo" by some, measured 5 feet by 5 feet and 15 feet deep.

She called the hole "one of the deeper voids" the state has encountered and said it's probably the result of a failed deep culvert: Storm drains and culverts can deteriorate over time, creating a slow leak that erodes the fine materials around the pipe.

The sinkhole first came to official attention with a call to police around 5:30 p.m. Thursday, according to Anchorage Police Department spokesman MJ Thim. More callers reported the hole "starting to open up" and measuring 4 feet by 3 feet wide.

Patrol officers arrived and found a hole that was 4 feet wide — and estimated it as much as 20 feet deep, Thim said.

Police set up detours and notified state transportation officials. There were no traffic issues reported Friday morning, he said.