Reconnaissance snow surveys of the National Petroleum Reserve in Alaska, April 1977 and April-May 1978

Abstract

Reconnaissance snow surveys of the NPRA (National Petroleum Reserve in Alaska) were made in April 1977 and April-May 1978 to ascertain general snow characteristics and distribution patterns. Thirty-nine sites in 1977 and forty-one sites in 1978 were sampled to determine snow depth, density, structure, and snow-soil interface temperature. In addition, snow surface wind indicators were examined over most of NPRA. In April and early May of two consecutive years, the snow cover in NPRA was thin, wind-packed, and virtually continuous. The depth and water equivalent of the snow generally increased with altitude and with distance from the coastal plain. Snow depth on tundra ranged from less than 0.20 m (meters) near the coast to more than 0.90 m in parts of the Brooks Range. Snow density was relatively high in areas where wind slab was developed throughout the snowpack, and lower where there was less wind slab. In 1977, the coastal plain showed the greatest wind slab development and higher densities, averaging 310 kg/cu m (kilograms per cubic meter) on tundra, while the mountains and foothills had less wind slab and lower densities, averaging 270 kg/cu m. In 1978, with more local variation, snow density on the coastal plain averaged 330 kg/cu m on tundra and averaged 310 kg/cu m in the mountains and foothills. Water equivalent of the snowpack in 1977 ranged from less than 0.10 m in the coastal areas to more than 0.25 m in the Brooks Range, and averaged nearly 0.12 m on tundra for the entire area. Water equivalent of the snowpack averaged more than 0.13 m in 1978. Snow-soil interface temperatures in 1977 ranged from about -20C on the coastal plain, where the snowpack was thin and ambient air temperatures were low, to about -5C in the mountains and foothills where the snowpack was thicker and ambient air temperatures higher. (Kosco-USGS)