Neighborhood Nature

Our Family's Nature Blog

How Did This Happen? Leaf-shaped Holes in the Snow February 4, 2009

Filed under: Plants,Puzzles and Mysteries,Trees — saltthesandbox @ 2:58 pm
Tags: , , , , ,

I was walking along the edge of Columbus Park golf course this morning when I noticed some leaves that seemed sunken into the snow:

Each leaf was in its own leaf-shaped hole, an inch or so below the surface.

Each leaf was in its own leaf-shaped hole, an inch or so below the surface.

Here is another example. Look at the edges of the hole.

Here is another example. Look at the edges of the hole -- there is a thin, lacy crust of snow that overhangs the edges of the leaf.

Can you figure out how this happened? Here’s some information that may be helpful:

  • Most leaves were from oak trees. Oaks often hold onto their leaves well into winter, until a strong wind blows them off.
  • The snow fell on several different days, and the last snowfall was only an inch or two thick.
  • The last few days have been mostly sunny, but the temperature has been mostly below freezing.
  • There were tracks of people, dogs, and squirrels near the leaf holes, but some leaves were far from the closest tracks.
  • In some places, the loose snow was coated with a crust of icy snow.

The next hint is an experiment for you to try. It requires one flashlight, one snowy yard, and one building.

  • Take a flashlight outside and cover the lens with half a snowball, holding it like this:
It looks like an ice cream cone -- but don't eat it!

It looks like an ice cream cone -- but don't eat it!

  • Now take the flashlight inside, still holding it lens up.
  • Take the snow-covered flashlight into a dark room and turn it on.
  • What you see may help you solve our puzzle

……………………………………………………………………..[Go here if you don’t have any snow.]

Finally, here’s an experiment that we had to do for you, because it requires two kittens:

Our two kittens, sleeping in the sun.

Our two kittens, sleeping in the sun.

  • Our family’s two kittens, Raff and Pumpkin, were sleeping in the sunny kitchen window.
  • Raff is black, and Pumpkin is pale orange and white.
  • If you petted both kittens, which would feel warmer?

……………………………………………………….[Hint: Darker colors absorb more of the sun’s heat.]

Here’s my best explanation of how the leaf prints formed:

  1. First a layer of snow fell, a few inches deep.
  2. Then oak leaves blew off the trees and fell onto the layer of fresh snow.
  3. Then more snow fell onto the leaf-flecked older snow, burying it under a few more inches of fresh, clean snow.
  4. Then the sun came out. The sunlight penetrated the clean, clear snow, going deep enough to hit the oak leaves below and warm them up.
  5. The warmed leaves melted the snow right above them, creating tiny snow caves that kept growing higher as the sun kept shining and warming the leaves. Because heat rises, the snow beyond the outer margins of the leaves did not melt — just the snow above the leaves.
  6. The snow caves eventually grew tall enough that their thin roofs of snow collapsed and melted back, becoming leaf-shaped holes — each with an oak leaf at the bottom.

Another explanation would be that the leaves sat on the snow surface, warmed in the sun, and melted the snow below them, gradually sinking deeper and deeper into the ice. But this hypothesis doesn’t fit with the photo above that shows a thin, lacy crust of snow projecting over the oak leaf.

Do you agree? If not, you can post your better explanation below. Either click on “Comments” in the lower right corner or use the “Leave a Reply” box if that appears below.

 

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