Urban Geocryology: Mapping Urban–Rural Contrasts in Active-Layer Thickness, Barrow Peninsula, Northern Alaska

The maximum depth of seasonal thaw is a critical design factor for civil infrastructure in permafrost regions. Although maps of active-layer thickness (ALT) have been created for localized areas in undisturbed terrain, this has rarely been done within urbanized areas. The modified Berggren solution was used to map ALT at a resolution of 30 × 30 m over the 150-km2 Barrow Peninsula in northern Alaska. Emphasis was placed on analyzing differences in accuracy obtained in urbanized and relatively undisturbed tundra. Although the modified Berggren solution is known to provide more accurate estimates of frost and thaw depth than the Stefan solution, it has not been used previously in mapping applications. As part of the Barrow Urban Heat Island Study, seventy-one miniature data loggers were installed in and surrounding the City of Utqiaġvik (formerly Barrow) to measure air and soil temperature. The resulting data were used to calculate air and soil surface temperature fields, as well as summer n-factors, based on nine urban and rural land-cover classes. Regional soil and land-cover maps were used to obtain additional input data. Validation was performed by comparing probed ALT measurements with predicted pixel values. Model results confirm that the presence of urban infrastructure increases both the magnitude and the geographic variability of ALT relative to surrounding undisturbed tundra. The Berggren solution performed well for estimating mean values for land-cover classes in both rural and urban areas and has considerable potential as a tool for mapping ALT in other applications. Key Words: active layer, Alaska, Barrow, frozen ground, geocryology, mapping, permafrost, urban, Utqiaġvik.