The edge of frozen or partially frozen ground. In areas of seasonal freezing with no permafrost, the freezing front moves downward through the earth. In areas of permafrost, the front can also move upwards: ‘during frost heaving of soil when the soil is freezing from the top down, water in the soil pores flows upward to the freezing front because of a gradient in the soil moisture pressure (or tension). This occurs even when the soil pores are not saturated. Ice lenses form and grow at or slightly above the freezing front and cause great uplifting forces’ (Henry (2000) US Army Corps of Engineers).
Subjects: Earth Sciences and Geography.