After volunteers on snow machines thoroughly exhausted the ground search for two missing snowmachiners in Big Lake, Alaska State Troopers turned their focus to efforts in the air Thursday, targeting areas with known water hazards.

Family members identified the missing riders as LaVerne and Van Pettigen in a Facebook post Tuesday afternoon, adding that they were last heard from just before 11 a.m. Sunday. They were reportedly riding "a 2000 Black Polaris 500 and a 2014 Yamaha Dark Blue Vector."

According to the couple's daughter LaTisha Wilkinson, the Alaska Air National Guard said the last cell signal picked up was Tuesday at 10:30 a.m.

Throughout Wednesday and Thursday, teams were searching the area from which the signal came, but did not find any signs of the missing couple.

Wilkinson said LaVerne is a born and raised Alaskan, while Van moved to Alaska in the 1970s while in the military. Both have been realtors for more than 20 years.

LaTisha said her parents have a condo in Big Lake and are both experienced snowmachiners. Their last phone message, at 10:53 a.m. Sunday, was a response from LaVerne to someone interested in viewing an Anchorage property.

"The lake has changed since the earthquake and there’s a lot extra open water, as well as there may be new warm springs," said Mark Stigar with Mat-Su Search and Rescue.

 Stigar said the Mat-Su Borough Dive Team has said the lake is hazardous now, even for those who know it well.

"They’ve been out here and done a lot of work out here and they say what’s scary is you’ve got three feet of ice, and then right next to it four inches of ice, all because of a warm spring coming up from the bottom," Stigar explained, adding, "And potentially with this earthquake, we could have more of those spots, so for people who are familiar with this area, it’s changed."

Stigar oversaw volunteer searches Thursday morning, making sure everyone signed in and was accounted for when groups returned.

"If you ever go out, you need to leave some sort of a trip plan because somebody needs to know where you are," he said, "Because here’s a case where we don’t even know where to look."

After leading a volunteer group, Dan Mayfield returned to the staging area for the search off of Big Lake Road around lunchtime feeling tired, ready for food and water, and disappointed they had found no clues.

"Everybody’s hopeful that we find these folks, but the longer it goes on and the colder it gets, you know, it does bring some questions to our mind," he said, "Whether or not we’re gonna be able to have a satisfactory conclusion to our search."

When Troopers arrived in the afternoon, they were confident the volunteer teams and troopers on snowmachines the day before had thoroughly checked the trails and nearby areas that are safe to access by snowmachine.

Alaska Wildlife Trooper Daniel Gunderson said their plan was to search more hazardous areas by air, including Saddleback Island and the canals between Flat Lake, Mud Lake, and Big Lake.

"That’s the areas that we’re gonna be hovering over, looking for tracks that go in and just disappear," Gunderson said.

He said weather conditions were presenting their greatest challenge.

"There was areas of open water that have now froze and have a little bit of snow on top of that, so it’s a challenge to determine exactly where that was," Gunderson explained.

Just before 3 p.m., the Mat-Su Borough Water Rescue team joined the search. Trooper Gunderson said they had found "new leads" that prompted them to call in the dive team.

But within less than an hour, the search had stopped. Troopers cited safety concerns as it grew dark, and said they will resume their efforts Friday morning at daylight.

The Pettigens' two daughters have arrived in Alaska, and went out with one of the search teams in the afternoon.

"Boy, my heart sure goes out to those folks," said Mayfield, "I really do hope we have a satisfactory conclusion."

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