Earth Surface Processes and Landforms Earth Surf. Process. Landforms 28, 87–98 (2003) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/esp.432 RECENT VENTIFACT DEVELOPMENT ON THE CENTRAL OREGON COAST, WESTERN USA JASPER KNIGHT 1 * AND HELENE BURNINGHAM 2 1 Glacial Research Group, School of Biological and Environmental Sciences, University of Ulster, Coleraine, Co. Londonderry, BT52 1SA, UK 2 Coastal & Estuarine Research Unit, Department of Geography, University College London, Chandler House, 2 Wakefield Street, London WC1N 1PG, UK Received 29 October 2001; Revised 13 June 2002; Accepted 25 July 2002 ABSTRACT The unusual location of ventifacts, on a boulder-built jetty at the mouth of the Siuslaw River, Oregon coast, western USA, allows ventifact age and wind abrasion rates to be estimated with some precision. The jetty was built mainly between 1892–1901 and extended throughout the twentieth century. Consideration of historical shoreline position and the history of jetty construction and repair suggests the ventifacts have formed since about 1930. Morphologically the ventifacts are aligned south-to-north reflecting winter winds and sediment transport from the adjacent beach. Wind-parallel grooves and ridges with sharp, sinuous crests are developed on inclined boulder surfaces on top of the jetty and reflect suspended sand transport in wind vortices. Deeply pitted surfaces on steep boulder surfaces nearest the beach reflect impact by saltating sand grains. Based on present wind regimes (1992–2000) from three regional weather stations, southerly winds above the sand transport threshold occur for 21Ð9–29Ð6 per cent of the time. Based on estimated depth of loss from boulder surfaces, wind abrasion rates are calculated to be on the order of 0Ð24–1Ð63 mm a 1 . This is the first well-constrained field estimate of ventifact age and ventifaction rate from a modern coastal environment. Copyright  2003 John Wiley & Sons, Ltd. KEY WORDS: ventifacts; Oregon; wind transport; wind abrasion rates; coastal dynamics INTRODUCTION Ventifacts (wind-etched clasts or bedrock surfaces) are features found commonly in modern coastal environ- ments where loose intertidal and supratidal sand can be blown onto and abrade adjacent rocks and boulders (King, 1936; Greeley and Iversen, 1985; Bishop and Mildenhall, 1994; Braley and Wilson, 1997). Despite many field observations of ventifacts from coastal and inland (arid and semi-arid) environments, however, there have been few estimates of the time-scale required for ventifaction (the process of ventifact develop- ment). Reasons for this may include the poorly defined and qualitative visual basis on which ventifacts are identified (Miotke, 1982), the range of possible time-scales (hours to millennia) on which ventifaction can take place (Kuenen, 1960; Miotke, 1982), and the relict nature of some ventifacts with respect to present-day winds (Schlyter, 1995). Ventifaction is also dependent on a range of environmental variables including wind approach angle and its constancy over time, sediment grain size and concentration in the windstream, and rock surface hardness (Schoewe, 1932; Lancaster, 1984; Greeley and Iversen, 1985), characteristics which are difficult to evaluate in the field. Accurately ageing ventifacts in the field is also necessary in order to quantify wind abrasion rates. An experimental plot set up by Sharp (1964, 1980) in an inland, semi-arid environment yielded abrasion rates which varied by a factor of four over different time-periods and on different lithologies. This present study uses historical, map and field data to evaluate ventifact development in a modern coastal environment in central Oregon, western USA. The unique setting of the ventifacts, on a boulder-built jetty which has a known construction and repair history, allows a detailed estimate of the time-period required for ventifact development, and thus estimates of modern wind abrasion rates. * Correspondence to: Jasper Knight, School of Biological and Environmental Sciences, University of Ulster, Coleraine, County Lon- donderry, Northern Ireland, BT52 1SA, UK. E-mail: j.knight@ulst.ac.uk Copyright  2003 John Wiley & Sons, Ltd.