April 11, 2011

The Fifth Season in New Hampshire

By Naturalist Eric D'Aleo

It’s getting to be that time of year again in New Hampshire, when people consider hanging up their snow shovels although winter is not quite ready to acquiesce that spring has actually arrived. This is the time of year that many who live in the northeast know as the fifth season of the year … mud season. There is no exact date for mud season, like the arrival of ice out on a lake; mud season’s arrival can vary depending on several variables. The severity of a winter, latitude and elevation of a location, the type of road, and its drainage and exposure to the sun can all affect how long the season lasts and when it begins. Mud season is characterized by large stretches of dirt roads that rapidly change from being hard and frozen in the early morning to a muddy quagmire in the afternoon that often requires a 4-wheel drive vehicle to safely pass over. However, they are not the only indication of the season; frost heaves are the asphalt equivalent to the muddy back roads. At these times bright orange signs warning of “frost heaves” or “load limits” seem to bloom spontaneously out of the snow banks on the sides of paved roads. Being an attentive driver is especially helpful at this time of year since an individual that does not heed them can experience the end result in unexpected wear and tear on a car’s suspension and a surprising shock to the driver’s nerves.

Both the prolific amount of mud and the frost heaves are caused by the alternate heating and freezing of the ground, which had been frozen all winter long. The ground’s surface thaws from the sun’s heat first, causing any water that has melted to percolate into the soil. It does not penetrate far before it encounters soil that is still frozen preventing further drainage. On a dirt road this results in a muddy trek during the day that just hours before had been a hard, frozen surface. A paved road with poor drainage and standing water may allow water to seep through the cracks in the asphalt or the road’s shoulders into the sub base of material underneath. During a cold early spring night the water under the road freezes forming an ice lens which draws super cooled water to it. This freezes upon the lens surface making it grow in size, pushing the soil and asphalt upward. If the heaving occurs unevenly due to the amount of water beneath, different parts of the road surface can crack. When the ice lens melts during the next warm period, there is little or no soil supporting the asphalt, but more water, so that when a large vehicle passes over the location, it will push the roads surface into the ‘soft spot,” weakening the material and creating a pothole. At this time of year when there are numerous freeze and thaw cycles over several weeks it can make the potholes grow larger, making any trip out of the driveway an adventure.

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