The Chattanooga Chapter has a great write up on what freeze-thaw is and why it's so bad. Freeze-thaw is why Blankets is closed this time of year. Please understand that we get more traffic in one day then most trails see in a month so we have to be very careful with the trails right now as opening them too soon will cause months worth of damage to the trails and only force us to keep them close longer.
From SORBA Chattanooga
Between abundant precipitation and very cold temperatures, off road enthusiasts have been largely kept off their bikes for weeks. After a long cold and wet month many mountain bikers are just itching to ride. The arrival of warmer weather means that many want to head out on to the trails right away.
Most mountain bikers understand riding a trail when wet and muddy can cause rutting, puddling and other forms of trail degradation. However, many of these same users don’t understand that trails are at even greater risk during the freeze-thaw process.
What is the freeze-thaw process?
During wet winter months, when the trial becomes saturated and temperatures drop, ice forms in soil voids. Through the night temperatures drop and the freezing process pushes soil grains apart reducing particle cohesion and soil strength and making the soil more erodible. During the day temperatures increase and the trail surface thaws.
Even though the surface has thawed, the ground is still frozen just below the surface. To make matters worse, the frozen ground prevents precipitation from sinking in any further. This means the thawed layer at the surface is absolutely saturated with water so it is very intolerant of any disturbance. Come riding along and you’ll cut through the thawed layer right down to the frozen ground. The thawed layer will end up with ruts from the tire tracks, which will persist even when the soil dries out.