GROTON -- Snow may seem cold and uncomfortable to humans. But for hibernating animals, snow pack is home-sweet-home.

Thirteen children attended the first "Science Saturday" workshop of 2013 on Saturday at the Nashua River Watershed Association Resource Center in Groton. The group participated in a hands-on experience about the natural insulating properties of snow in a class called "The Science of Snow and Ice."

NRWA Education Director Mary Marro started the workshop with a closer look at the shape of snowflakes, which is "just oxygen and hydrogen bonding together," or crystalized water.

"When it's really cold, they're flat crystals," said Marro. "When it's warmer, you get star-shaped snowflakes. And when it's very warm, sometimes you get what's called snow needles."

The shapes are clearer to see if one wears dark-colored clothing when snow falls, said Marro. Fallen snow compacts and may lose the shape the crystal had when it was falling.

The students climbed into snow gear and were given clear cup-sized containers which they'd marked with their prediction -- how much water would be left in the cup when the loosely-packed snow they loaded into the cups thawed.

"There is a lot of air in the snow," Marro hinted.

Later, the class loaded plastic film rolls (now an antique, joked Marro) with a couple of inches of liquified cherry-flavored Jell-O.

The experiment was to determine which of two canisters would freeze -- Jell-O buried under a snow pack or laying on the surface of the snow. The children broke into teams of two and three to stake the snow along the wooded trail where they'd buried their fruit-flavored research project.

In the interim, and manned with Celsius thermometers, the children took the ground-level versus the surface temperature of the snow.

"Under the snow is actually warmer than on top of the snow," summarized Marro of the teams' results. And this is why animals like the snow weasel can burrow and tunnel under the snow cover and eat hibernating animals like young rabbits, chipmunks and rodents.

The children also came across deer tracks in the woods and spotted a clear patch in the snow where there were battered bits of pine cone atop the snow. Marro noted it looked like a squirrel party had just taken place atop the tree.

"He was probably sitting right up there and eating the pine nuts," said Marro. "They're not edible to us but they are to the squirrels."

One girl gathered up an armful of "cone on the cob" remnants -- dozens of rachis, or the center axis of the pine cone, where the seeds are located.

Back to the Jell-O canisters, Mother Nature threw a curve ball.

Saturday's temperatures were rather mild and rivaled the ground level temperature. The Jell-O began setting up in both instances. No bother -- the children dipped their finger into the mixture to marvel at how quickly the natural refrigerator had worked on the project.

The pitcher of Jell-O, likewise, began to harden while the tour of the woods was under way.

Marro shrugged. "It would be a bit better if it were a colder day."

The children didn't mind in the least. Gazing off in the distance, the solid snow was vaporizing -- a process known as sublimation, where it becomes gaseous without passing through a liquid phase (the opposite process -- gas to solid ice -- is known as deposition).

Next up, emulating a burrowing, hibernating animal. The throng got busy building tunnels adequately sized for small animals to travel in. Marro also took out a long tube and pushed it into the snow pack to illustrate how snow can have different characteristics the deeper and more compact it becomes.

"They can see the layers of snow over the years," said Marro.

"Sometimes they find microscopic animals, too," said Stacey Chilcoat, the NRWA Classroom director.

Back inside, the children wrapped their workshop with a look at the snow melt recorded in their cups. They added different substances to determine the effect on the snow. Of particular interest was adding vinegar and baking soda to watch the resulting bubbling chemical reaction atop the snow, and how salt melts snow down to slush. 

The Nashua River Watershed Association will host a workshop for families on Saturday, Jan. 19, from 1 to 2:30 p.m., which will focus on wildlife that can be found in your backyard. The workshop includes encounters with live animals. The event is free, but registration is encouraged by calling Pam Gilfillan at 978-448-0299 or pamg@nashuariverwatershed.org.

NRWA offers year-round seminars for the public. Details are at www.nashuariverwatershed.org.

Follow Mary Arata at twitter.com/maryearata.