When the snow above the active layer melts, the water remains on the surface of the soil. This is because water cannot be absorbed by the permafrost, leaving the top layer of the soil wet and soggy. Evaporation of the water is also not possible. The arctic tundra's cool air does not promote much Evaporation from taking place. The arctic tundra landscape is formed by the freezing, thawing and refreezing of this soggy soil. This type of land formation is only unique to the arctic tundra. There are five types of distinguishable land formations by the power of freezing water: pingos, frost boils, bumpy ground, polygons, and stripes.
Pingos are hills which are formed by ponds of water that were trapped underground by permafrost. Yearly, as the ponds thaw and then freeze, a hill above the ground grows taller and taller. They can grow up to 150 feet (146 meters) tall.
Frost boils are ever widening circles of stones caused by the thawing and freezing of water. As water thaws and freezes, large rocks are pushed out and form expanding rock circles on the active layer.
When variations in ground thawing and freezing occur because of plant cover, rocks, or small ponds, bumpy ground is formed. As all these different sections of ground cover pull and push against each other, bumps, along with tiny valleys and hills can form in the ground.
Polygons are geometric land shapes that are between 10 to 100 feet (3 to 30 meters) wide and are outlined by cracks filled with water. These cracks can deepen and widen forming streams and the occasional shallow pond. Stripes occur on hillsides when thawing and freezing cause rocks to be sorted by particle size.
Thawing and freezing of water is not the only force shaping the arctic tundra. Earthquakes shake the ground and volcanoes shape mountains. Gravity also plays an important role. The water which causes the arctic tundra's soggy ground flows downhill. This slow downhill flow of water is called solifluction. Solifluction is an assurance of the tundra's ever changing land.
The alpine tundra's soil also has a layer of permafrost, but its active layer is not as soggy as the arctic tundra's. This is because rainfall in the alpine tundra runs off of the steep mountain sides instead of becoming saturated in the soil. Strong winds also sweep moisture from melting snow out of the soil leaving the top layer dry and dust like in the summer.
The alpine tundra of course is made up of mountains either formed by volcanoes, the collision of continental plates, or by retreating glaciers. These mountains are always being changed by earthquakes, strong winds, mud slides, and avalanches.