Mud Season and the Springtime Thaw

Winter is giving way to spring, and our pathways will be subjected to freeze-thaw cycles until the ground is free of ice. This means that inspecting trail conditions during the transition from frozen to entirely thawed will be more crucial. Mud season is what we call it in the major whiskey, and it normally starts in March and lasts for 4-8 weeks. You can ride open trails ethically during the period when the ground is frozen solid. It's worth looking past the air temperature to the dew point to see if the earth is frozen solid. The ground will be smooth and hard if the dew point is below 25 degrees Fahrenheit. The next factor to think about is cloud cover. By 8:00 a.m., direct sunshine will have begun to defrost the ground, especially if there is no snow cover to reflect it. This time of year, the ideal times to find frozen solid trail conditions are at night or very early in the morning.

What's all the fuss about freeze-thaw cycles?

Because cooler temperatures hinder the soil from drying, dirt trails are especially sensitive to rut damage during the transition to and from winter. A sub-layer of earth has also remained frozen, preventing surface water from draining. Mud pudding is created by the surface layer of soil and meltwater. When topsoil freezes, ice crystals form, pushing soil particles apart and creating enormous gaps that can fill with water when the ice melts. When thawed, this earth acts like a sponge, absorbing vast volumes of water. It is also quite sensitive to disturbances such as foot/bike traffic and streaming water, and will easily produce ruts. Direct sunlight and temperatures above freezing during the day can defrost the top layer of frozen dirt, resulting in a rutted, greasy, muddy mess on the surface. Lower temperatures overnight refreeze the top surface of the trails, including ruts, and the process continues when conditions permit (hence the name freeze-thaw cycle).

Why are ruts bad for trails?

When ruts form on a route, they channel water, causing trail surface erosion and slowing the drying process. When the subsoil is frozen, rain is extremely erosive on trails, and ruts greatly increase the likelihood of erosion by running water. When the subsoil is frozen, water cannot soak in as it should and instead runs in vast amounts along the surface. These flows can be intercepted and diverted along the length of a route by ruts. As the water travels down the trail and speeds up, earth particles are picked up and washed away from the trail. In extreme cases, this can result in tens or hundreds of feet of deep ruts. Ruts can keep pools of water on the route surface in the spring, preventing it from drying as rapidly. If bike tires disrupt these puddles, they can quickly turn into enormous mud pits. Volunteer time spent on these areas should be better spent on other initiatives. Trail closures are also extended in wet regions like this.

Riding tips for the winter/spring months, when temperatures swing between freezing and above freezing:

• Keep an eye on the trail conditions - if the temperature is above freezing, don't ride frozen paths.
• Ride icy trails first thing in the morning before they warm up, or at night when the ground is completely frozen.
• If the temperature is below freezing and it is sunny, don't ride. Wait until the temperature is below 28 degrees Fahrenheit and the dew point is below 25 degrees Fahrenheit. Even then, if there is direct sunlight, there may be thawed portions.
• If the trails are still too soft after following all of the above suggestions, turn around and try again. In these conditions, a single rider can wreak havoc on thousands of feet of terrain.