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The location and extent of icings observed during six winters, 1969 to 1974, along the trans-Alaska pipeline route are shown on a series of maps and photographs. Large flood-plain icings occur in the braided river channels of the Sagavanirktok, Atigun, Dietrich, and Delta Rivers. Numerous lesser stream and hillside icings also occur along the pipeline route. Construction of the pipeline, roads, pumping stations, and training structures will displace some existing icings and will create new icings. Icings may cause problems such as flooding and erosion when they form on or near the pipeline, roads, and other pipeline facilities. INTRODUCTION A 48-inch (122-cm) diameter pipeline to transport petroleum from the Prudhoe Bay area on Alaska's North Slope to the ice-free port of Valdez in Prince William Sound is now under construction. The northsouth route of the pipeline (fig. 1) transects the major physical features and climatic zones of Alaska, and thus a wide range of hydrologic conditions will be encountered. This report discusses icings, also called aufeis, which are masses of ice formed by the overflow and subsequent freezing of sheets of surface water and emerging ground water. Icings can cause severe problems when they form on or near highways, airfields, or other structures. Some of these problems may be (a) the diversion of surface water by the ice and the consequent flooding and erosion by ice and water and (b) impaired traffic flow on surface transportation routes. This report also discusses the distribution and general types of icings along the pipeline route. The severity of icing problems that may be found during the construction and operation of the pipeline system is related to the character of the icings within any section of the route. The aerial observations and photography upon which this report is based were obtained principally during light-aircraft flights along the trans-Alaska pipeline route during the months of March, April, or May in the years 1969-74. Observations were not made on the same date each year; flight lines, altitudes, snow cover over icings, and weather conditions (thus the visibility) differed somewhat for each set of observations. The maps are a compilation of all icing observations made during the 6-year period. Not all icings shown on the maps were present on any given date. However, nearly all icings shown occurred each winter. Some of the smaller icings did not form annually, and all icings varied in areal extent and thickness from year to year. Satellite and thermal infrared imagery was examined for evidence of winter overflowing of rivers, of ice remaining in early summer, and of midwinter temperature anomalies. The aerial observations of icings along the pipeline corridor confirmed that the remote sensing techniques show icings. The 6-year record of observations indicates that not all icings can be observed on one airplane trip; likewise, no one set of remote sensing imagery shows all icings or the maximum extent of icings. The remote sensing imagery did not reveal any unknown or unsuspected icing areas along the pipeline corridor. Periodic icing observations and inventories should be continued during the construction and operation phases of the trans-Alaska pipeline system. Such a monitoring program will permit the detection of significant changes in natural icings and the initiation of any new icings along the pipeline route. For those readers who may prefer to use metric units rather than English units, the conversion factors for the terms used in this report are listed below: Multiply English units' By To obtain metric units inches (in.) 2.540 centimetres (cm) feet (ft) 0.3048 metres (m) PRINCIPLES OF ICING FORMATION An icing is a mass of surface ice formed during the winter by the successive freezing of sheets of water that seep from the ground, from a river, or from a spring (A. M. Chekotillo, 1940, in Carey, 1970). Carey (written commun., 1967, 1968) has collected and analyzed data on icings in Alaska. He has discussed in detail the origin, formation, engineering significance, and techniques for study and control of icings (1973) and has compiled an annotated bibliography on these topics (1970). The following general statements about icings are derived from these publications and from the authors' observations. ICINGS ALONG THE TRANS-ALASKA PIPELINE ROUTE

Icings along the Trans-Alaska Pipeline route