Tuesday, June 2, 2015

Frost Heaves

 Note: This program first aired April 25, 2015. 

It seems this year that spring has come with an abruptness that has startled even the most optimistic among us. Day after day of warm sunlight, no fire in the wood stove, and a snowpack that gets smaller with every hour. Each day brings with it a new sign of spring, first the turkey vultures appeared, now the alders are shedding pollen, the skunk cabbage are in bloom, the phoebes have returned, the chipmunks are out, the osprey are back. Every winter we forget it is possible, and every spring is such sweet relief and wonderment.

One sign of spring that I think we could all do with out, save those kids sitting in the back seats of the school bus, is the return of frost heaves to the back roads so many of us drive every day. I happen to live within a mile of the official “Worst Road in Maine 2014”, Rt. 15 in Blue Hill, so I know of what I speak. A year later, the roads aren’t as bad, but still require vigilance and restraint if you hope to come through the season with axels and wheels intact.

Frost heaves are a function of the interplay of water and the road bed, liquid water, frozen water and soil that has just the right amount of capillarity. When winter sets in the ground freezes from the top down, a frost front moves down into the soil, freezing the water in the soil in to a solid mass. In the spring that frozen water starts to melt, especially during the day, only to freeze again at night. We end up with a layer of ice sandwiched between a thawed surface layer and an unfrozen deep layer below the frost line. The interplay between the frozen layer and the unfrozen soil below it results in the bumpy driving this time of year, and the pot holes we contend with the rest of the time.  

People used to think that a frost heave was simply a function of solid water taking up move volume than liquid water, a phenomenon I have experienced more than once when I left a full water bottle in my car over night in sub freezing temperatures. Liquid water expands when it freezes, and as a result, those water bottles don’t work any more. With frost heaves, we have learned that the increase in ice volume isn’t enough to account for the destruction that occurs. The ice volume is part of it, but so is the ready supply of liquid water that happens most commonly in the spring. As more and more snow and ice melts, there is more and more liquid water around to feed the sub surface ice. As long as it stays cold enough for the ice to keep freezing at least some of the time, the liquid water running beneath it feeds those ice crystals, and they grow upward. Most of us have seen these crystals bursting out of bare soil or gravel. The asphalt on the road surface is essentially impermeable though, so the ice crystals can’t thrust up through it, and they cause the road surface to bulge up. And there is our frost heave. If the road heaves up enough, the asphalt cracks, and those cracks become the starting points for pot holes that will form later, after the ice has melted away.

On the road surface the unevenness of the frost heaves are an indicator that the fill used in the road bed is inconsistent, or that ground water is interacting with the road bed in some places but not others. That’s why simply repaving doesn’t solve the problem for more than a few months. To address the underlying issue the entire road has to be dug up and rebuilt, which takes time and money and can cause a huge inconvenience.

To me though, the frost heaves, though annoying, represent an opportunity. They remind me to slow down as the pace of life speeds up as we head into the long days of summer. And they show me that the transition from winter to summer can be rough, not just for me, but for the earth under my feet as well. And just like my life, once summer arrives the roads smooth back out, perhaps a little worse for wear, but no longer bucking me off every journey I attempt.