a slope), among other materials. Syngenetic ice wedges may only form if the thermal contraction and subsequent ice-veinlet growth can keep pace with the addition of new material. If this is the case, the ice wedge can reach depths of 25 meters, but the average is much less. In a syngenetic ice wedge, the age of the ice on the periphery decreases upwards. Anti-Syngenetic Anti-syngenetic ice wedge were first observed in 1990 during the fieldwork of J. Ross Mackay. Mackay found that anti-syngenetic grew in conditions opposite to those of syngenetic ice wedges in that the anti-syngenetic variety required the removal of material instead of the accumulation and addition of material. Anti-syngenetic ice wedges only form on slopes, where there is a net loss of materials erosion. Similar to syngenetic ice wedges, anti-syngenetic ice wedges can only occur if the rate of thermal contraction cracking and ice-veinlet growth keeps pace with the removal of active material. Anti-syngenetic ice wedges therefore only grow downwards, penetrating deeper into the soil only as the upper layers are removed by mass wasting and erosion. In an anti-syngenetic ice wedge, the age of the ice on the periphery increases upwards. References Periglacial landforms Patterned grounds Permafrost