Morphogenesis of Soils Associated With Frost Boils

Frost boils are a kind of nonsorted circles commonly found in arctic and alpine regions. In early studies of the Northern Alaska Arctic Coastal Plain, frost boils were found more frequently on moist nonacidic tundra (MNT) than on moist acidic tundra (MAT). But a recent study indicates that frost boils are widespread on both land cover types. Although MNT has more frost boils with mineral soils exposed forming an easily recognizable circle that is generally free of vegetation (mud boils). Crossing the transition from MNT to MAT, there is increased vegetation cover on frost boils. In well-developed MAT, vegetation cover masks frost boils. Once the vegetation cover is removed, frost boils are clearly defined by ice ring ridges underneath the inter boil moss layer. These frost boils are active as indicated by chunks of cotton grass (Eriophorum vaginatum) in various stage of decomposition that are found frost churned in along the slopes of the ice ridges toward the upper permafrost. In the lower active layer and the upper permafrost there are concentrations of frost churned organic matter mixed with gleyed mineral horizons. Thus, frost boil process can be regarded as the controlling factor in the sequestration of surface produced organic matter through its incorporation into the upper permafrost for both MNT and MAT. There are drainage differences due to micro relief across the frost boil sequence. In summer, the elevated center of the frost boil is moderately well drained as compared with the poorly drained inter boil due to its depression position. The active layer depth in the center of the frost boil is generally more than twice that of the inter boil, thus the permafrost table surface forms a nearly perfect bowl shape. The lower active layer has strongly developed reticular cryogenic structure. The upper permafrost is ice-rich, generally containing more than 65% ice (vol.) and has ataxitic cryogenic structure. The thickness of the ice-rich layers in the ridges beneath the inter boil area is much greater than that beneath the boil center. In addition, the cracks and the ice veins are parallel to the slope of the ice ridge. Although there are different theories regarding the initiation of frost boils and different factors are involved in frost boil self-organization, morphological evidence in the field suggests that the thick ice formation under the inter boil causes long-term heave of the frost boil and forms its shape.