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Unexpected science lessons fresh from the rain in Alaska

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Posted: Saturday, November 10, 2012 11:46 pm | Updated: 12:10 pm, Mon Jan 21, 2013.

LAKE MINCHUMINA, Alaska — In November 2010, after a late but otherwise fairly normal freeze-up, 1 and 1/2 inches of rain fell in three days. The rainwater flowed off the hills to accumulate on the lake ice, making me worried about the safety of the ice.

During the spring thaw, snowmelt collects on lake ice faster than it can drain off, but we don’t worry about going through the slush. It takes a long time for 2 1/2 or 3 feet of ice to thaw and rot, and by then the surface water has long since flowed underneath the ice, leaving it almost dry.

That unprecedented November rain falling on just 7 inches of lake ice was different. We didn’t venture out on the lake with the rain coming down, but as it tapered off to a light mist we began to think about our fish net, set under the ice two miles away.

My sister Miki was determined to check the net, but the ice worried me. It had been strong black ice prior to the storm, but now warm rain water was sitting on top with lake water sandwiching it from below. I knew it took weeks for spring ice to rot, but I had never experienced so much water covering such thin ice on the lake before.

I was thinking about the rain, which may have been much warmer than 32 degrees, thawing the ice from above. Although unlikely, heat might still be radiating upward from the lake bottom to rot the ice from below as well. The lake had been ice-covered for a few weeks and was probably stable, but the possibility still worried me.

The run-off had joined melted snow already on the frozen lake. As the water deepened it weighed down the ice that was naturally trying to float. If the standing water didn’t freeze, it could take days to work its way down through holes and cracks as the lake ice slowly rose toward equilibrium.

Many years ago, I went to check a fish net beneath young ice covered with a couple inches of overflow water and was horrified to find the ice dangerously rotten, apparently thawing from both above and below. That ice wasn’t very thick, though. Neither was the rotten ice back in October of 1981 when as a youngster I broke through into water over my head. I could well have died there if I hadn’t been able to grab my dog, who pulled me out. Those experiences made me cautious.

Was the lake ice dangerously rotten now? Miki didn’t think so. I wasn’t so sure. I called our neighbor Tom, who with 40 years on the lake, had lived here almost as long as we had. He sided with Miki — the ice should be OK — so we loaded our fishing equipment into a high-sided plastic sled and set off to see if we could reach the net.

After three-quarters of a mile the lake appeared beyond the silt flats, mottled with gray slush and black water instead of white snowdrifts. Grateful for our tall rubber boots, we waded through 5 to 10 inches of water and sloshed slowly toward Holek Spit where our net lay under the ice. Slipping on the slick ice and sometimes breaking through a skim of surface ice, we moved slowly to avoid falling and getting drenched.

The black plastic sled floated lightly behind me with our ax and ice chipper, fish picks, rubber gloves, sacks for hauling the fish and extrication rope should someone fall in. We knew the underlying water was shallow for a few hundred yards where the silty river delta gradually slanted downward, but as we passed over onto deeper water I grew more nervous and reached for the ice chipper to test the ice.

The ice felt comfortably solid, only a little soft as my chipper splashed through the surface water into the ice below. I chose a spot with 12 inches of standing water and even though I cut through a frozen swamp gas bubble for easy chopping, it took some whacking to punch into the lake water.

I peered through the surface water to inspect the quality of the ice. It looked clean and clear, not pocked or cloudy. Then I saw something strange. I leaned closer, jaw agape. “Come here! Look at this!” I called to Miki.

We hunkered down over the hole, staring in fascination. Each little methane bubble rising from the lake bed would hit the lower edge of the ice at the hole and get stuck. Instead of floating up to be released into the air, it would cling to the ice under the surface water for a second or two and then would sink.

The pressure differential between the ice trying hard to float, and the surface water trying to sink, created a powerful suction pulling the water down through the hole. The buoyant swamp gas bubbles couldn’t fight the terrible drag and sank along with the down-flowing stream.

After admiring this phenomenon, we waded on, wondering how we could pick fish from the net while standing shin-deep in water. Luckily, a small area of water-free ice surrounded the anchor post near the beach. It gave us a dry spot to pick fish, though we still had to wade to the far end to pull the rope that hauled the net back underwater.

The long wade home with the plastic sled/boat floating behind passed so easily that we made a side trip across the river delta to check a second net, uncommonly pleased to finish those chores under challenging conditions. The day made an enjoyable adventure, but once is enough. We’ll be hoping for cooler weather this year.

Trappers and lifelong Bush residents Miki and Julie Collins have written three books, which are available at Gulliver’s Books in Fairbanks. They live in Lake Minchumina.

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