With temperatures in single digits this week, it may be tempting to lace up the ice skates and slide around Anchorage's lakes, but officials with the Parks and Recreation Department say not so fast.
Ice near the edges of Westchester Lagoon measured two inches thick on Monday, according to Holly Spoth-Torres, city parks superintendent. It's still ten inches away from the foot of ice required for the parks department to send out a maintenance vehicle and officially open the lagoon for skaters.
Until the ice thickens, the cautionary signs will remain at the municipality's six freshwater rinks.
"People need to be really careful this time of year," Spoth-Torres said.
Two inches of ice is the minimum required for one person on foot or skates to safely go on freshwater ice, according to ice safety standards from the U.S. Army Corps of Engineers. For a group of people walking in a single file line, it's 3 inches . The parks department also uses these guidelines, Spoth-Torres said.
But the minimum standards only apply to ice where there isn't water flowing underneath. That's not the case for maintained places like Westchester Lagoon, Cheney Lake and Goose Lake. Here, thickness will vary across the ice because of water flow.
The added instability is why the city parks department waits until ice builds to a foot, instead of the required nine inches under the U.S. Army standards, before driving the pick-up truck across the surface. The truck weighs about two tons and carries 350 gallons of water which adds another 3,000 pounds to its weight, Spoth-Torres said. It's used to regularly hot-mop the skating rinks and remove snow.
And until the parks department can officially maintain the rinks, they will not be officially opened, Spoth-Torres said.
But parks officials will continue to regularly monitor the ice thickness and update the Ice and Trail Status Report on the municipality's website. Employees use an auger, like one used in ice fishing, to drill holes in various locations of the freshwater lakes, pond and lagoon. This season, maintenance crews took their first stab at the weekly measurements on Monday. But the preliminary findings weren't recorded, Spoth-Torres said. It's too early in the season. For all of the freshwater rinks the website currently reads: "Ice is not safe, please use caution."
Maintenance crews will take a measurement of the ice early next week, Spoth-Torres said. But with a warm spell expected this weekend and temperatures nearing the freezing mark, she doubts the minimum ice thickness for the truck will form by Monday or Tuesday.
Ignoring variables, as temperatures decrease below 32 degrees, ice becomes thicker quicker, according to Jim Pantaleone, professor and chair of the Department of Physics and Astronomy at the University of Alaska Anchorage.
But the rate of ice formation depends on a number of things like snow presence, which acts as an insulator, and how fast heat is transmitted through the water, he said.
Pantaleone also noted water's special property that prevents it from freezing from the bottom up.
Above 39 degrees, water behaves like most everything else when it gets cold, he said. It shrinks, becomes more dense and sinks to the bottoms of lakes, ponds and lagoons.
But at 39 degrees and below, water begins to expand, becomes lighter and rises to the top of the body of water. At 32 degrees this top layer starts to freeze.
Reach Tegan Hanlon at thanlon@adn.com or 257-4589.
By TEGAN HANLON